Sponsorship Statement: Publication of this supplement is sponsored by the ACNP.

Presenting author disclosures may be found within the abstracts. Asterisks in the author lists indicate presenter of the abstract at the annual meeting. Abstract numbers do not correlate to poster number assigned for presentation at the Annual Meeting.

P276. Deconvolving Cell Type Proportions in Human Postmortem Brain Tissue From Bulk RNA-Seq Data

Louise Huuki*, Kristen Maynard, Stephanie Hicks, Peter Zandi, Joel Kleinman, Thomas Hyde, Fernando S. Goes, Leonardo Collado-Torres

Lieber Institute for Brain Development, Baltimore, Maryland, United States

Background: The brain contains a wide variety of structures, that in turn are made up of many different cell types with individual complex functions. Bulk RNA-seq from tissue homogenates obscures this complexity. Deconvolution seeks to estimate the composition of cell types in the sequenced tissue to examine biological differences between samples, or minimize confounding technical variables, such as differences in dissection, in downstream analysis.

Methods: Reference snRNA-seq Dataset

For the reference single nucleus RNA-seq dataset we utilized the data set from Tran et al. (https://doi.org/10.1101/2020.10.07.329839) which includes 70,615 high-quality nuclei across five human brain regions: nucleus accumbens (NAc), amygdala (AMY), subgenual anterior cingulate cortex (sACC), hippocampus (HPC), and dorsolateral prefrontal cortex (DLPFC). The ten cell types considered in the deconvolution of the tissue were Astrocytes (Astro), Endothelial (Endo), Macrophage (Macro), Microglia (Micro), Mural cells, Oligodendrocytes (Oligo), Oligodendrocyte Progenitor Cells (OPC), T cells, Excitatory Neurons (Excit), and Inhibitory Neurons (Inhib).

Cell Type Marker Gene Selection

To give the algorithms the best change of accuracy, we selected for highly specific genes to each cell type, ideally only expressed in the target cell type. To achieve this, we developed a marker selection strategy: calculating the ratio of the mean expression of each gene in the target cell type over the highest mean expression of that gene in a non-target cell type. The top 25 genes for each cell type were selected.

Deconvolution Algorithm Selection

We considered two different deconvolution methods: MuSiC (https://doi.org/10.1038/s41467-018-08023-x) and Bisque (https://doi.org/10.1038/s41467-020-15816-6), which showed strong performance (https://doi.org/10.1038/s41467-020-19015-1). MuSiC claims to be good for differentiating between closely related cell types, and Bisque showed the highest performance in their benchmark analysis on DLPFC data. Deconvolution was performed with MuSiC version 0.2.0 and the ReferenceBasedDecomposition function from BisqueRNA version 1.0.4, using the use.overlap = FALSE option.

Bulk RNAseq Datasets

We performed deconvolution on eight, in-house, post-mortem, human brain, bulk RNAseq datasets; spanning 5,787 samples, in seven brain regions (DLPFC, sACC, AMY, HPC, Caudate, Dentate Gyrus, and Nucleus Acumbens), and four diagnoses (MDD, Bipolar, SCZD, and control), as well as the GTEx v8 brain dataset. We will focus here on the deconvolution of the MDDseq data set containing 1,091 samples, with 704 (459 MDD, 245 Bipolar) cases and 387 control samples, from the sACC and AMY (Synapse syn22276064).

Results: Marker finding

The set of marker genes we identified is highly specific, confirmed by visualizing violin plots of gene expression over cell type, heat maps of pseudo-bulked cell type from each donor, and t-tests comparing against all other cell types (FDR < 5%). The resulting set of marker genes overlaps eight known marker genes (https://doi.org/10.1038/s41586-019-1195-2) and identifies new data driven marker genes (96%).

Method selection

We observed that MuSiC is highly sensitive to the set of marker genes, while Bisque is robust. Bisque also returns cell fraction estimates that were concordant with expected regional variability (https://doi.org/10.1101/2021.01.21.426000).

MDDseq results

The Bisque estimated cell type proportions showed a difference in means across diagnoses (MDD, Bipolar, control) for either brain region (AMY, sACC) in 22 out of 60 pairwise t-tests (testing ten cell types, in two brain regions, between three diagnoses; p.bonf < 0.05). Between samples from male and female donors 6 out of 20 t-tests are significant (testing for ten cell types, in two brain regions; p.bonf < 0.05). However, the effect size of the differences is minimal. Correlation analysis of the cell type proportions vs. quality surrogate variables (qSV) (https://doi.org/10.1073/pnas.1617384114) revealed qSVs may already adjust for variation in cell type composition. Each cell type has a significant correlation (p.bonf < 0.05) to at least four of the top ten qSVs.

Conclusions: We found that the mean ratio marker selection performed better than previous gene marker selection strategies. Based on the nine datasets and the expected cell type composition variability across human brain regions, we found Bisque to be the most accurate of the available deconvolution methods. The results reported for the MDDseq dataset represent a pattern of results seen in the other bulk RNA-seq human brain datasets.

Keywords: RNA-seq, Deconvolution, Single-Nucleus RNA-seq, Human Post-Mortem Brain, Bisque

Disclosure: Nothing to disclose.

P277. Setting the Stage for Chemogenetic Manipulations of Whole Brain Resting State Functional Connectivity in Nonhuman Primates

Adriana Cushnie*, Ana Manea, Jan Zimmermann, Sarah Heilbronner

University of Minnesota, Saint Paul, Minnesota, United States

Background: Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) are modified G-Protein Coupled Receptors that can be targeted to select neuronal populations. Once expressed, pharmacological activation of DREADDs with a chemogenetic ligand allows for transient, remote, and reversible manipulation of cells expressing the receptors. Clozapine-N-Oxide (CNO) is commonly used to activate DREADDs, however, CNO demonstrates poor brain permeability, requiring large doses to be administered and is metabolized into clozapine. Recent studies have shown that low dose clozapine (CLZ) and novel ligand Deschloroclozapine (DCZ) have a higher affinity for DREADDS with minimal off-target binding. The utilization of DREADDs in nonhuman primates (NHP), though limited in comparison to studies using rodents, allows for the causal perturbation of targeted cells in a model species with brain structures more similar to those found in humans. Functional Magnetic Resonance Imaging (fMRI) is a non-invasive neuroimaging approach that measures fluctuation in hemodynamic signals locally and across the whole brain. fMRI has identified altered functional connectivity in many neurological and psychiatric disorders.

The aim of this study was to lay the groundwork for combining DREADDs manipulation with resting state fMRI in NHP. To this end, we first determined the infection and transport patterns of common AAV serotypes in macaques (see Cushnie et al., 2020).

Methods: We evaluated the effects of chemogenetic ligands on resting state functional connectivity prior to DREADDs transduction in NHP. Macaques underwent a series of resting state fMRI and structural MRI scans at 10.5 Tesla at UMN’s CMRR. Acutely before the start of each scan, Macaca fascicularis (n = 2, female), received a systemic injection of chemogenetic ligand (DCZ 0.1mg/kg, DCZ 0.2mg/kg, CLZ 0.1mg/kg, CLZ 0.2mg/kg) or vehicle. NHPs were anesthetized with ketamine (10 mg/kg intramuscularly), and subsequently they were intubated using 1% isoflurane and monitored using standard physiological monitoring. For functional imaging, we used a simultaneous multi-slice gradient echo planar imaging approach at 0.75 mm isotropic with whole brain coverage (MB = 2, GRAPPA = 3). We collected resting-state data for 6 runs, ~2 hours/session.

Functional connectivity based on gradient and spin echo (T2* and T2) imaging was analyzed using a custom pipeline of a combination of FSL, AFNI and the CONN toolbox; neuroimaging software. Images were corrected for motion distortion using mcflirt (images are registered to the first image). Images were corrected for echo planar imaging distortions resulting from long readout trains using FSL topup. Slice scan time correction was applied to adjust for offsets in image time acquisition using a custom written C + + routine. Lastly, images were corrected for physiological artifacts through a multi-step denoising pipeline. Global white matter, CSF, and venous blood time courses were estimated using singular value decomposition and combined with respiration and heart rate. All images were analyzed in their original reference space.

Results: We examined whole-brain changes in resting-state functional properties after systemic injections of vehicle or chemogenetic ligand. Specifically, we assessed changes in functional connectivity and intrinsic timescales. Resting-state functional connectivity is characterized by temporal correlations between spontaneous blood oxygenation level-dependent (BOLD) signals. Intrinsic timescales, a fundamental local property, are temporal fluctuations in the neural signal that are task and variable independent. Thought to reflect the amount of temporal integration of a region, intrinsic timescales are closely related to the brain’s functional hierarchy. fMRI has identified altered functional connectivity and intrinsic timescale patterns in many neurological and psychiatric disorders.

The relationship between functional connectivity and drug is highly correlated between subjects, suggesting a relatively consistent change in resting-state functional connectivity in response to drug conditions (for both DCZ and CLZ). Functional connectivity between subjects is least correlated during vehicle conditions (most likely due to individual innate differences) and the highest correlation is observed following administration of CLZ doses. Compared to CLZ, DCZ has a lesser effect on functional connectivity and may be best suited for future studies. These results were also consistent for intrinsic timescale analysis.

Conclusions: This proof of principle study revealed local and whole-brain functional connectivity patterns prior to DREADDs expression, setting the stage for more detailed network interrogation using chemogenetic manipulations and resting-state fMRI in NHPs.

Keywords: Chemogenetics, Functional MRI (fMRI), DREADDs, Brain Anatomy

Disclosure: Nothing to disclose.

P278. Glucocorticoid-Priming of Inflammatory Response to LPS Challenge in Microglia

Andrew Bartlett*, Galen Missig, Erica Jarrell, Angelica Carillo, Emma Fritsch, Miles Damon, Torsten Klengel, William Carlezon

Harvard Medical School McLean Hospital, Belmont, Massachusetts, United States

Background: Glucocorticoids are renowned for their immunosuppressing effects. The immunomodulatory effects of glucocorticoids have been shown to extend to microglia, altering both their morphology and function. However, previous reports have largely focused on the acute effects of glucocorticoids on microglial processes. Glucocorticoids tend to produce an "inverted-U" dose-response with varying effects depending on the time-scale of treatment (acute versus chronic). Here, we examined the long-term effects of acute glucocorticoids on microglial responses to immune challenge.

Methods: We used mouse BV2 microglial cells as an in vitro model to examine the effects of glucocorticoids on the immune-activating effects of lipopolysaccharide (LPS). To examine LPS-induced alterations in chromatin and transcription within microglia, we administered the synthetic glucocorticoid dexamethasone (10nM), cross-linked chromatin after 90 min for glucocorticoid receptor (GR) chromatin immunoprecipitation (ChIP), and collected RNA for RT-qPCR after 180 min. We also co-treated cells with both LPS (1.0 µg/ml) and dexamethasone (10 nM) for 24 hr, and collected media for ELISA to quantify inflammatory cytokines and RNA for RT-qPCR. Additionally, we compare these results with microglia isolated from two in vivo manipulations of the glucocorticoid system, acute dexamethasone (10mg/kg, IP, 4 hr) and chronic social defeat stress ([CSDS], 10 days) in male C57BL/6J mice. Following each manipulation microglia were isolated using magnetic cell sorting for the microglia/brain macrophage marker CD11b and then RNA was isolated for RT-qPCR. Group differences were examined using unpaired student’s t-tests.

Results: Dexamethasone treatment upregulated expression of mRNA encoding the clock gene period 1 (Per1) (p < 0.05) and the kappa-opioid receptor (KOR; Oprk1) (p = 0.05), a receptor previously implicated in responsiveness to stress, in microglial BV2 cells (n’s = 5 plates per group). Consistent with previous findings, we found that co-administration of dexamethasone and LPS attenuated release of Il-1ß from microglia compared to release following treatment with LPS alone (p < 0.05, n’s = 3 plates per group). In our in vivo manipulations, acute dexamethasone significantly downregulated Il-1ß (p < 0.01) and upregulated Oprk1 (p < 0.01) in microglia, whereas following a 10-day CSDS paradigm there was an upregulation of Il-1ß (p < 0.01) and downregulation of Oprk1 (p < 0.05) (n’s = 6-8 per group).

Conclusions: These experiments demonstrate the potential for glucocorticoid-regulated gene expression to have lasting effects on microglia activation. We found initial evidence that acute glucocorticoids can have a differential effect on proinflammatory cytokines with acute dexamethasone decreasing Il-1ß expression, whereas CSDS enhanced Il-1ß expression in microglia. Interestingly, we found that dexamethasone elevated levels of Oprk1 mRNA, consistent with previous reports indicating that KORs are expressed in microglia and regulated by stress. Expression of KORs on microglia, where they would presumably act to inhibit inflammatory processes, is important considering that KOR antagonists are currently being evaluated as treatments for depressive illness, which has previously been associated with inflammatory processes. Future work will examine the mechanisms by which these responses are regulated, including measuring GR binding to response elements upstream of both cytokines and Oprk1 as well as the mRNA expression following co-treatment of dexamethasone with LPS to determine if there are alterations in GR binding at GR response elements. Additionally, we will overexpress Oprk1 in BV2 cells to examine if lasting effects of glucocorticoid-treatment on microglial inflammatory responses are mediated by glucocorticoid-induced Oprk1 expression.

Keywords: Glucocorticoid, Microglia, Kappa Opioid Receptor

Disclosure: Nothing to disclose.

P280. Dose Dependent Effects of Transcranial Photobiomodulation on Depression Severity in Major Depressive Disorder

Paolo Cassano*, Aura Maria Hurtado, Katherine Collins, Maia Beth Gersten, Luis DeTaboada, Julie Clancy, Molly Irvin, Allison Sparpana, Elizabeth Sullivan, Xiaotong Song, Arwa Adib, Joan Camprodon, Dan Iosifescu

Massachusetts General Hospital, Boston, Massachusetts, United States

Background: Transcranial photobiomodulation (t-PBM) with near-infrared (NIR) light penetrates into the cerebral cortex and is absorbed by the mitochondrial enzyme cytochrome c oxidase (CCO), stimulating the mitochondrial respiratory chain. t-PBM also significantly increases cerebral blood flow (CBF) and oxygenation. Small studies have reported that t-PBM may be an effective treatment in major depressive disorder (MDD). However, relationships between t-PBM dose (irradiance and/or total energy) and clinical or biological effects are unclear. In this experimental medicine study, we evaluated the dose-dependent, clinical effects of t-PBM in MDD subjects.

Methods: We enrolled subjects meeting DSM-5 criteria for MDD, not treatment-resistant (0-2 failed antidepressants in the current episode), either unmedicated or on stable doses of antidepressants, with no other significant medical or psychiatric comorbidities. All subjects underwent 4 t-PBM sessions, 1 week apart, administered in random order, with either sham or 3 combinations of t-PBM parameters: 1) Pulse wave (PW), average irradiance 300mW/cm2, 42Hz, 33% duty cycle, 4.3 KJ total energy; 2) Continuous Wave (CW), 300 mW/cm2 irradiance, 2.4 KJ total energy; 3) “Low dose”: CW, 50 mW/cm2 irradiance; 1.4 kJ total energy. Other t-PBM parameters were kept unchanged (808 nm; 12.0 cm2 × 2 treatment area; delivered to the prefrontal cortex, bilaterally, corresponding to the F3 and F4 electrode location). All subjects were rated by study investigators for their depression severity with the Montgomery-Asperg Depression Rating Scale (MADRS) at baseline and one week after each t-PBM session. Each t-PBM, dose-specific, antidepressant effect was assessed by computing the change in the MADRS total score from baseline to one week after the index t-PBM dose. The mean changes in MADRS total scores obtained after each t-PBM dose were compared to the effect of sham (paired t-test, with significance at 0.05).

Results: We analyzed data from the first 15 MDD subjects (11 White, 1 Black, 1 Asian, 2 Multiracial and 2 Latinos; age = 34.6 ± 11.3; 60% female) undergoing all 4 experimental sessions. We found that a single session of either PW (delta -5.7 ± 9.4, p < 0.04), CW (delta -6.9 ± 8.6, p < 0.01) or “low dose” CW (delta -5.9 ± 6.5, p < 0.01) was more effective than sham (delta -2.0 ± 8.4). CW appeared to be slightly better (>25% decrease in MADRAS total score) than PW (21%) or “low dose” CW (22%), however these differences were not statistically significant.

Conclusions: These findings suggest that a single session of t-PBM might induce significant antidepressant effects within one week of treatment. This is important as t-PBM could become a candidate treatment to expedite antidepressant response in patients with MDD. The data also suggest that specific parameters of t-PBM (CW rather than PW, higher irradiance and higher total energy) might be more effective. More clarity on the latter point will likely arise when the complete sample (n = 30) is analyzed.

Keywords: Transcranial Photobiomodulation, Near-Infrared Light, Neuromodulation, Neurostimulation, Depression

Disclosure: Niraxx Light Therapeutics Inc, Stock / Equity, Board Member, Advisory Board, Founder (Self)

P281. Associations Between Altitude, Suicidal Ideation, and Depressive Symptoms Among University Students in the Healthy Minds Study

Brent Kious*, Shawna Sisler, Edward Diener, Douglas Kondo, Deborah Yurgelun-Todd, Perry Renshaw

University of Utah, Salt Lake City, Utah, United States

Background: There is increasing evidence that suicide rates in the U.S. and other countries are associated with altitude of residence, with higher suicide rates in high-altitude regions like the Rocky Mountain West. The psychopathological mediators of this association remain poorly characterized, with mixed findings regarding associations between altitude and depression. To attempt to replicate findings linking altitude and suicide and to shed light on possible psychopathological underpinnings of that association, we examined correlations between altitude of residence, suicidal ideation, suicide attempts, depressive symptoms, and previous diagnoses of depression in a large retrospective dataset of university students in the Healthy Minds Study.

Methods: We obtained data for 260,967 students from the Healthy Minds Study, which a large multiyear anonymous cross-sectional database of university students, including multiple sociodemographic measures, psychiatric symptom scales such as the PHQ-9, and self-reported lifetime history of suicidal ideation and attempts. Altitude, latitude, and longitude for each campus were determined using Google Earth. Moran’s I was calculated for each outcome variable to determine whether it was spatially autocorrelated. Correlations between altitude and self-reported diagnoses, suicidal ideation, suicide attempt, PHQ-9 score, and PHQ-9 item 9 (suicidal ideation) were estimated using a mixed model with repeated measures a spatial Gaussian covariance structure, with individual sociodemographic variables treated as fixed effects. Multiple imputations were utilized to address missing data.

Results: 53% of participants were women, 65.8% Caucasian, 94.5% enrolled in a four-year program, and the average age was 22.5 (+ 5.2) years. The average altitude was 255.7 (+ 358.9) m. The mean PHQ-9 total score was 16.0 (+ 5.6). Moran’s I indicated each outcome variable was spatially autocorrelated. In geographically-weighted mixed models, and after correction for multiple hypothesis testing, altitude was significantly correlated with any diagnosis of depression (p = 0.0014), a diagnosis of bipolar depression (p = 0.0022), but not a diagnosis of major depressive disorder. However, the interaction between gender and altitude was strongly significant, and major depressive disorder was significantly positively correlated with altitude for women but not for men. Similar results obtained for bipolar depression. PHQ-9 total score was significantly and positively correlated with altitude (p < .0001). PHQ-9 item 9 was also significantly correlated with altitude (p = 0.007) and the interaction terms of altitude with a history of depression was significantly correlated with PHQ-9 item 9. Lifetime suicide attempt was significantly correlated with altitude (p < .0001), although lifetime suicidal ideation was not.

Conclusions: Our results are consistent with previously published population-level evidence of an association between altitude of residence and various forms of psychopathology, including suicide, but augment those findings by examining outcomes among a large nationally-distributed sample of young adults who have provided individual psychometric data. Our results also identify, for the first time, statistically significant associations between altitude, depressive symptoms as measured by the PHQ-9, and an historical diagnosis of depression. We observed particularly significant associations between altitude and a diagnosis of bipolar depression. Consistent with findings from previously published animal studies, the effect of altitude on depressive diagnosis was greater for women than men. Our results reinforced findings that increasing altitude is associated with increasing risk of suicide, as we observed that past-week suicidal ideation as measured by PHQ-9 item 9 was significantly correlated with altitude, and that a history of suicide attempt was associated with altitude. The study was limited by several factors. First, the altitude to which participants were exposed could only be inferred from the altitude of their campus. Second, although participants reported their year in school, the duration of their exposure to the local altitude was unknown, as it was unknown whether they had previously resided near the university or at a similar altitude. Similarly, assessment of suicidal behavior (suicide attempts) was limited to participants’ lifetime self-reported history; it was unknown, however, whether reported suicide attempts occurred while the participant was enrolled at the university or when they were residing elsewhere. Finally, the magnitudes of the associations with altitude observed in our study were, although consistently significant, usually small. Nevertheless, these findings support previously identified links between suicide rates in the United States and altitude, imply that increases in depressive symptoms may mediate this association, especially in women and in persons with bipolar disorder, and argue for the importance of further investigating mechanisms by which altitude could contribute to psychopathology.

Keywords: Suicide Risk Factors, Major Depression Disorder, Altitude Disclosure: Nothing to disclose.

P282. Alterations in the Functioning of Striatal Subregions are Associated With Anhedonia as a Function of Striatal Dopamine Concentrations in Adolescents With Depression

Cecile Ladouceur*, Pat Brosseau, Teague Henry, Amar Ojha, Rasim Diler

University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Background: Depression affects about 20% of adolescents and substantially increases the risk for suicidality, substance abuse, as well as academic and interpersonal difficulties. It is a heterogeneous condition with varying degrees of severity and course, but little is known about the etiological processes underlying clinical features and outcome. Anhedonia, including loss of interest, motivation, and pleasure, is a core symptom of depression that has been associated with poorer treatment response and worse overall outcomes. Adolescent depression and anhedonia have been associated with changes in reward-related behaviors and alterations in the dopaminergic reward system, including the striatum. However, it remains unclear whether specific patterns of alterations in the functioning of the striatum may be associated with anhedonia relative to other symptoms of depression. To address this gap, we examined, in a sample of adolescents with varying levels of depressive symptoms, whether resting state striatal regional homogeneity ̶ an index of regional synchronization generally shown to be reduced in adult depression ̶ was associated with symptoms of anhedonia and to what extent this relationship may be moderated by striatal dopamine concentrations.

Methods: Consistent with the NIMH RDoC framework, adolescents between 12-17 years old (n = 75; 46 females) were recruited to participate in this study. They were oversampled for clinically high levels of depression, with 56 adolescents scoring ≥ 40 on the Children’s Depression Rating Scale-Revised (CDRS-R) and 19 adolescents having no current or past psychiatric diagnosis, and no parent with a psychiatric diagnosis. Participants completed a clinical interview, self-report measures, and an fMRI protocol that included two 6 min. resting state sessions. Adolescents reported symptoms of anhedonia using the Snaith-Hamilton Pleasure Scale (SHAPS) and symptoms of depression using the Mood and Feelings Questionnaire (MFQ). Resting state fMRI data was preprocessed using fMRIprep 20.1.1. Regional homogeneity (ReHo), a measure of intrinsic, local connectivity at a voxel-level spatial scale, was calculated within the striatum. Mean standardized T2* was calculated within the striatum and is used as a proxy for (inverse) tissue iron concentration, which in turn acts as a proxy for dopamine concentration. To examine the relationships between ReHo, mean T2* intensity, and anhedonia symptoms, we used a voxel-wise moderated mediation approach controlling for age, sex, and symptoms of depression (excluding items on the MFQ assessing anhedonia). A clusterwise permutation approach was used to control the familywise error rate.

Results: After controlling for age, sex, and other depressive symptoms, we found a significant moderation effect indicating that striatal tissue iron concentration moderated the relationship between ReHo and anhedonia within the bilateral caudate and the left putamen. Simple slopes revealed that reduced ReHo was associated with higher levels of anhedonia in adolescents with higher levels of tissue iron concentration in the right caudate (peak T = 4.17), and with lower levels of anhedonia in adolescents with lower levels of tissue iron concentration in the same region (peak T = 2.99). Lower tissue iron concentration in the left putamen was associated with higher levels of anhedonia overall (peak T = 2.79).

Conclusions: Findings indicate that a specific pattern of alterations in striatal neurobiology is associated with anhedonia in adolescents with varying levels of depressive symptoms. Namely, intrinsic connectivity in subregions of the striatum is associated with anhedonia but the direction of this relationship is contingent upon levels of striatal dopamine concentrations. While there is a need to determine the underlying mechanisms, such findings point to the need to examine whether dopamine-targeted pharmacotherapy may be particularly effective for a subset of adolescents with depression characterized by anhedonia. They also signal the need to deepen our understanding of the development of the striatal dopaminergic system in adolescent depression. Future work will examine to what extent these patterns of striatal functioning predict trajectories of anhedonia symptoms over 2 years.

Keywords: Adolescent Depression, Striatum, Dopamine, Anhedonia, Resting State Intrinsic ConnectivityDisclosure: Nothing to disclose.

P283. Preference for Extrasynaptic GABA-A Receptors Conveys a Wider Therapeutic Window Between Anxiolytic and Sedative-Like Effects in Rats for the Positive Allosteric Modulator, PRAX-114, Compared With Zuranolone

Zoe Hughes*, Liam Scott, Kristopher Kahlig, Marion Wittmann

Praxis Precision Medicines, Inc., Cambridge, Massachusetts, United States

Background: Neuroactive steroid (NAS) positive allosteric modulators of GABA-A receptors (GABAAR PAMs) are demonstrating promise as rapid acting antidepressants with potential to address the unmet need in major depressive disorder (MDD). The antidepressant effects of NAS are thought to depend on potentiation of extrasynaptic GABAAR because benzodiazepines (BZs), which only interact with γ-subunit-containing GABAAR (predominantly synaptic GABAAR), are anxiolytic but not antidepressant. As α1 subunit-containing synaptic GABAAR mediate the sedative effects of BZs, we hypothesized that an extrasynaptic GABAAR-preferring NAS would be better tolerated due to reduced activity at this subtype of synaptic GABAAR.

Here we compare PRAX-114, a novel extrasynaptic GABAAR-preferring PAM, to zuranolone, another NAS in clinical development for MDD. To determine whether extrasynaptic preference results in an improved therapeutic window, the effects of both compounds on EEG β-frequency were measured as a translational biomarker of GABAAR activation and related to brain concentrations associated with anxiolytic and sedative-like effects.

Methods: Positive allosteric modulation of GABA-induced current (IGABA) by PRAX-114 and zuranolone were measured using manual patch clamp in vitro electrophysiology in CHO cells expressing human extrasynaptic (α4β3δ) or synaptic (α1β2γ2) GABAAR (n = 6-11/concentration).

Effects of PRAX-114 (0.3-10 mg/kg) and zuranolone (0.3-3 mg/kg) on β-power were measured in a cohort (n = 8) of telemetered rats using a cross-over design. Anxiolytic effects of PRAX-114 (1-10 mg/kg) and zuranolone (0.1-3 mg/kg) were evaluated in the conditioned emotional response (CER) assay in rats (n = 12-13).

Effects of PRAX-114 (3-30 mg/kg) and zuranolone (1-3 mg/kg) on 5-choice serial reaction time (5-CSRT) responding were assessed in rats as a sensitive measure of changes in attention (n = 12). Finally, effects of PRAX-114 (10-60 mg/kg) and zuranolone (3-30 mg/kg) on rat spontaneous locomotor activity (sLMA) were assessed as a surrogate for sedative-like side effects (n = 10).

Brain concentrations of PRAX-114 and zuranolone were measured using mass spectroscopy in tissue collected from satellite rats. Terminal samples were collected from a subset of rats after sLMA.

Results: PRAX-114 potentiated IGABA at extrasynaptic (EC50 353nM; Emax 910%) and synaptic (EC50 2241nM; Emax 1789%) GABAAR, indicating a 6.3-fold preference for extrasynaptic receptors in terms of potency. Zuranolone potentiated extrasynaptic (EC50 106nM; Emax 993%) and synaptic (EC50 293nM; Emax 3237%) IGABA, but with only a 2.8-fold preference for extrasynaptic receptors. In terms of efficacy, PRAX-114 had 10.5-fold less PAM activity at synaptic vs. extrasynaptic GABAAR, at a concentration (262 nM) achieving PAM activity equivalent to the maximal GABA effect at extrasynaptic GABAAR. Equivalent in vitro profiling of zuranolone (60 nM) indicated a 2.6-fold preference for activity at extrasynaptic receptors.

PRAX-114 achieved dose-dependent increases in β-power (F4,34 = 31.72; P < 0.0001) in rats. There was a strong relationship between brain concentration and β-power fold increases 1 h post-dose, with a 1.6-fold increase achieved at an interpolated brain concentration of 1205 ng/g and dose of 4.5 mg/kg. Zuranolone also produced dose-dependent increases in β-power (F3,21 = 53.00; P < 0.0001), with a 1.6-fold increase achieved at a brain concentration of 352 ng/g and a dose of 0.7 mg/kg.

PRAX-114 (F3,36 = 12.24; P < 0.0001; ED50 3.2mg/kg) and zuranolone (F3,33 = 13.85; P < 0.0001; ED50 0.5mg/kg) both increased CER suppression index to ~0.5 indicating robust anxiolysis. The brain concentration of PRAX-114 at the CER ED50 (EC50) was 305 ng/g, a concentration interpolated to produce a 1.1-fold increase in β-power. For zuranolone, the CER EC50 was 66 ng/g; similarly interpolated to produce a 1.1-fold increase in β-power.

Dose-dependent decreases in the number of trials completed in the 5-CSRT task were observed for PRAX-114 (F4, 55 = 18.98; P < 0.0001) and zuranolone (F4, 55 = 8.93; P < 0.0001). Brain concentrations associated with a 50% reduction in trial number (EC50) were 2756 ng/g for PRAX-114 and 355 ng/g for zuranolone.

For PRAX-114, the ED50 (59 mg/kg) for reduced locomotion (F3,36 = 3.89; P = 0.0166) was associated with a brain EC50 of 14460 ng/g, 47-fold higher than the EC50 for anxiolysis. For zuranolone, the ED50 for reduced locomotion (9.9 mg/kg; F3,36 = 20.72; P < 0.0001) corresponded to a brain EC50 of 1598 ng/g, 24-fold higher than the EC50 for anxiolysis.

Conclusions: When compared side-by side, PRAX-114 had greater preference for extrasynaptic GABAAR than zuranolone (~2-fold and 4-fold greater in terms of potency and efficacy, respectively). The relationships between brain concentrations required to increase β-power, and those associated with anxiolytic effects, were similar for the 2 molecules suggesting that extrasynaptic preference does not limit anxiolytic activity. Interestingly, in the 5-CSRT task, the PRAX-114 EC50 was calculated to achieve a 2.3-fold increase in β-power, whereas the zuranolone EC50 achieved only a 1.6-fold increase in β-power. Consistent with this, the separation between brain concentrations associated with reductions in sLMA and anxiolytic effects was ~2-fold greater for PRAX-114 than zuranolone. The data presented support our hypothesis that greater preference for extrasynaptic GABAAR results in improved tolerability without compromising anxiolytic efficacy.

Keywords: Rapid Antidepressant, Novel Therapeutics, Efficacy and Tolerability, Neuroactive Steroid, AnxiolyticsDisclosure: Praxis Precision Medicines, Inc.: Employee, Stock/Equity (Self).

Pfizer Inc: Stock / Equity (Self)

Biogen: Employee, (Spouse)

P284. The Role of Lactate Metabolism in Bipolar Disorder: Preliminary 7T MRSI Data

Michele Bertocci*, Victor Yushmanov, Chan Hong Moon, Halimah Abdul-Waalee, Amelia Versace, Mary Phillips, Boris Birmaher, Hoby Hetherington, Jullie Pan

University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Background: Bipolar disorder is a devastating psychiatric disease affecting 2-5% of people. Abnormalities in mania-related and depression-related behavioral energy are principal features of bipolar disorder suggesting energy metabolism dysfunction may play a role. Lactate is an energy source that is produced adaptively to compensate for low oxygen availability and is efficiently used by mitochondria and astrocytes, yet its role in neural function is unclear. Lactate was considered to be a biproduct of anaerobic metabolism however recent work has shown that its therapeutic use by infusion in traumatic brain injury (TBI) results in structural and cognitive improvement in humans and rodents, suggesting lactate plays an important and poorly understood role in neural health and functioning. Precuneus is a metabolic hot spot, is related to both task positive (cognitive, emotional, and theory of mind) activity and task negative (i.e., consciousness, introspection, and memory) activity, and precuneus dysfunction has been shown to be related to bipolar disorder. Our comparison region, the dorsal anterior cingulate cortex (dACC) is a task positive region that is established in the literature as important for differentiating bipolar disorder from healthy during emotion processing and other tasks. Furthermore, failure to deactivate this region during rest has recently been shown to be related to elevated depression in youth at risk for bipolar disorder. We aim to aid in understanding mania-related and depression-related behavioral energy in bipolar disorder through an examination of lactate availability. We examine lactate availability in precuneus compared to the better characterized dACC during an emotion processing task and during rest. Given the findings of improvements in neural health related to TBI with lactate infusion, and inconsistent lactate findings related to bipolar disorder, we expect reduced lactate in bipolar participants relative to healthy participant and we explore relationships with current mania and depression scores.

Methods: Eight adults (3 male) (mean age = 22.11, SD = 3.61) with controlled pediatric onset bipolar disorder and 1 male healthy adult (age = 27.67 years) from the Course and Outcome of Bipolar Youth (COBY) study were recruited for this study. Magnetic Resonance Spectroscopic Imaging (MRSI) was acquired on a 7-Tesla scanner using a 16-channel transceiver array, MP2RAGE imaging, and a fast homonuclear edited spectroscopic imaging sequence to detect the 1.3ppm lactate (Lac) both during an emotional face processing task (4 X 3 minutes 12 seconds) and during resting state (4 X 3 minutes 12 seconds). Lac is expressed as ratio to the creatine (Cre) resonance. On scan day, clinical depression and mania measures were collected using the Center for Epidemiologic Studies Depression scale (CES-D) and Altman Mania Rating Scale (AMRS) respectively. We used one sample t-test for bipolar disorder participants using the healthy participant test value and used correlations to examine relationships with mania and depression scores.

Results: Coby participants showed reduced task related precuneus Lac/Cre availability: mean = .054 (.03), range: 0.017-0.086, t(6) = -3.93, p = .008, Cohen’s d = .03 relative to healthy male Lac/Cre availability = .102 and reduced precuneus Lac/Cre availability during rest: mean = .040 (.02), range: 0.017-0.080, t(6) = -9.55, p < .001, Cohen’s d = .02 relative to healthy male Lac/Cre availability = .115.

Coby participants showed reduced task related dACC Lac/Cre availability: mean = .020(.01), range: 0.013-0.038, t(4) = -22.43, p < .001, Cohen’s d = .01, relative to healthy male Lac/Cre availability = .148 and reduced dACC Lac/Cre availability during rest: mean = .043 (.02), range: 0.016-0.070, t(4) = -3.67, p = .021, Cohen’s d = .03, relative to healthy male Lac/Cre availability = .084.

Higher subthreshold mania at scan was related to higher dACC task related Lac/Cre availability (Spearman’s rho = .949, p.014) all other ps > .423. Higher subthreshold depression was trend related to lower dACC rest related Lac/Cre availability (r = -.868, p = .056) all other ps > .377.

Conclusions: Preliminary results suggest that lactate availability in key neural regions may differentiate bipolar disorder from healthy and may be related to mania-related and depression-related behavioral energy. Lactate availability was lower in well-controlled pediatric onset bipolar disorder adults, relative to healthy adult, in both regions of interest, precuneus and dACC. Additionally, higher dACC lactate availability during emotion processing was related to higher subthreshold mania and lower dACC lactate availability during rest was trend related to higher subthreshold depression scores. Findings suggest that lactate availability in key neural regions may represent a novel feature of bipolar disorder diagnosis relative to healthy and lactate availability may be differentially related to key symptoms of bipolar disorder. Larger samples could clarify these preliminary results.

Keywords: Bipolar Disorder, MRSI, Lactate, Precuneus, dACCDisclosure: Nothing to disclose.

P285. Sex Differences in Sleep, Mood and Brain Functional Connectivity in Alcohol Use Disorder

Rui Zhang*, Corinde Wiers, Peter Manza, Dardo Tomasi, Ehsan Shokri Kojori, Mike Kreich, Erika Almira, Melanie Schwandt, Nancy Diazgranados, Reza Momenan, Nora Volkow

National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland, United States

Background: Growing evidence suggests greater vulnerability of women than men to the adverse effects of alcohol on mood and sleep. High sensitivity to the aversive consequences of drinking on sleep and negative affect might accelerate the progression into AUD in women. However, the underlying neurobiological mechanisms are still poorly understood.

Methods: Here we examined sex difference in resting state functional connectivity (RSFC) in alcohol use disorder (AUD) using a whole-brain data driven approach and tested for relationships with self-reported sleep and mood. To explore whether sex effects vary by AUD severity, we studied two separate cohorts: non-treatment seeking n = 70 AUD participants (29 females) from the Human Connectome project (HCP), and recently detoxified n = 102 treatment seeking AUD participants (34 females) at the National Institute on Alcohol Abuse and Alcoholism (NIAAA), who were older and had greater AUD severity than HCP participants. For RSFC analyses, a significance level was set at FWE-corrected p < .05 using non-parametric Threshold Free Cluster Enhancement approach (TFCE).

Results: Women with AUD reported greater sleep problems than men with AUD (pFWE = .005 and .048), while sex differences in mood were only observed in severe AUD (pFWE < .001). Sex differences in RSFC were distinct in low and high severity AUD participants. While sleep problems in women with low AUD severity were associated with increased cerebellar RSFC with salience (SN) and sensorimotor networks (SMN) presumably resulting in hyperarousal; for women with severe AUD, sleep and mood problems were associated with reduced RSFC between SN and visual network, presumably reflecting internally directed attention.

Conclusions: The current study revealed sex differences in RSFC that relates to sleep and mood problems in women with AUD. AUD severity modulates sex differences in sleep, mood and RSFC, which might reflect neuroadaptive processes with AUD progression that needs to be tested with longitudinal data in the future.

Keywords: Alcohol Use Disorder, Sex Differences, Resting State Functional Connectivity, Sleep, MoodDisclosure: Nothing to disclose.

P286. Dose Dependent Effects of Transcranial Photobiomodulation on Brain Hemodynamics in Major Depression

Dan Iosifescu*, Jacek P. Dmochowski, Katherine Collins, Aura M. Hurtado, Luis DeTaboada, Matthew J. Hoptman, Molly Irvin, Allison Sparpana, Elizabeth Sullivan, Xiaotong Song, Arwa Adib, Julie A. Clancy, Maia B. Gersten, Paolo Cassano

NYU School of Medicine, New York, New York, United States

Background: Transcranial photobiomodulation (t-PBM) with near-infrared (NIR) light penetrates into the cerebral cortex and is absorbed by the mitochondrial enzyme cytochrome c oxidase (CCO), stimulating the mitochondrial respiratory chain. t-PBM also significantly increases cerebral blood flow (CBF) and oxygenation. Small studies have reported that t-PBM may be an effective treatment in major depressive disorder (MDD). However, relationships between t-PBM dose (irradiance and/or total energy) and clinical or biological effects are unclear. In this experimental medicine study, we evaluated the dose-dependent effects of t-PBM in MDD subjects.

Methods: We enrolled subjects meeting DSM-5 criteria for MDD, not treatment-resistant (0-2 failed antidepressants in the current episode), either unmedicated or on stable doses of antidepressants, with no other significant medical or psychiatric comorbidities. All subjects underwent 4 t-PBM sessions in the MRI scanner, 1 week apart, administered in random order, with 1) sham (no energy emitted); 2) High dose: Pulse wave (PW), average irradiance 300mW/cm2, peak irradiance 900 mW/cm2, 42Hz, 33% duty cycle, 4.3 KJ total energy; 3) Medium dose: Continuous Wave (CW), 300 mW/cm2 irradiance, 2.4 KJ total energy; 4) Low dose: CW, 50 mW/cm2 irradiance; 1.4 kJ total energy. Other t-PBM parameters were kept unchanged (808 nm; 12.0 cm2 × 2 treatment area; delivered to the anterior prefrontal cortex, bilaterally). Resting state multi-echo (3), multi-band (2) fMRI was recorded on a 3T Siemens Trio using a 12ch head coil (TR = 2500ms, TE1 = 12.8ms, TE2 = 32.33 ms, TE3 = 51.86 ms, 60 slices, slice thickness 2.5mm) before, during and after t-PBM, using measures of the change in blood-oxygenation-level dependent (BOLD) signal on fMRI as marker of target engagement (t-PBM effect on cerebral blood flow). The BOLD signal was preprocessed using standardized automated tools [AFNI]. In order to test whether t-PBM modulated the BOLD signal during and after tPBM, we performed a region-of-interest (ROI) analysis taking into account the illuminated region of the brain. We extracted the signal from the transverse frontopolar giry, bilateral (ROIs 6 and 81 from the Desikan atlas) and separated the resulting time series into the pre-, peri-, and post-stimulation segments. We then performed spectral analysis in order to measure the BOLD power during each segment, employing the Thomson multitaper technique to increase the signal-to-noise ratio of the ensuing power estimates. This produced three spectra for each echo and dose (before, during, and after stimulation). We then tested for significant differences in BOLD power spectrum both during and after stimulation in each t-PBM dose, compared to sham (Wilcoxon rank sum test, corrected for multiple comparisons by controlling the false discovery rate at 0.05).

Results: We analyzed data from the first 7 MDD subjects (age = 32.1 ± 13.1; 57% female) undergoing all 4 experimental sessions. We found a dose-dependent effect of t-PBM on the BOLD. Namely, low-intensity t-PBM produced a marked decrease in BOLD that was observed in all three echos (p < 0.05, n = 7). The reduction in BOLD was most pronounced near 0.03 Hz at echos 2 and 3. In contrast, CW 300 mW/cm2 t-PBM increased BOLD power, with a significant increase resolved near 0.1 Hz at all 3 echos (p < 0.05, n = 7). This suggests that higher irradiance CW t-PBM increased the power of the “fast” component of the BOLD signal during stimulation. However, no significant differences from sham were observed during PW 300 mW/cm2 stimulation. We were also not able to detect any significant BOLD changes after tPBM (at any echo or t-PBM dose).

Conclusions: We found a U-shaped, dose-dependent effect of t-PBM on the BOLD, with the medium dose leading to an increase in the hemodynamic effect. These findings suggest that specific parameters of t-PBM (total energy, irradiance, CW versus PW) modulate the effect of near-infrared light on cerebral blood flow. This is important, as t-PBM doses optimized for their hemodynamic effect might also offer superior clinical efficacy.

Keywords: Photobiomodulation, Hemodynamic Effect, BOLD fMRI Signal, Irradiance, Total Energy

Disclosure: Allergan, Biogen, Jazz, Sage: Consultant (Self)

Otsuka: Contracted Research (Self)

P287. Neural Processes of Inhibitory Control in American Indian Peoples are Associated With Reduced Mental Health Difficulties

Evan White*, Mara Demuth, Mariah Nacke, Namik Kirlic, Rayus Kuplicki, Phillip Spechler, Timothy McDermott, Danielle DeVille, T1000 Investigators, Jennifer Stewart, John Lowe, Martin Paulus, Robin Aupperle

Laureate Institute for Brain Research, Tulsa, Oklahoma, United States

Background: American Indian (AI) populations suffer from substance use disorder and suicide at rates disproportionately high relative to the general population. However, our understanding of these increased rates is limited by a lack of contextualization of the risk factors unique to AI by the extant literature. Sociopolitical and historical contexts of these populations drive increased risk burden (e.g., low socioeconomic status, trauma exposure) among AI communities. Intriguingly, when researchers account for relevant risk factors AIs often display equivalent or lower rates of mental health concern than the general population. Furthermore, research indicates that AIs also experience high levels of positive mental health factors. Combined, these finding indicate that despite high levels of risk burden for psychopathology, AIs may exhibit protective factors against mental health difficulties. Although some public health literature suggests that cultural factors (i.e., spirituality, connectedness) may benefit well-being and be associated with lower mental health difficulties, this is an understudied area particularly with respect to potential neural mechanisms of these effects. Inhibitory control has a well-established neuroscientific profile and has been associated with lower levels of mental health difficulties. The goal of the current work is to investigate the impact of risk factors on prevalence of suicide risk (SR) in a sample of AI individuals and examine inhibitory control as a potential mechanism of mental health protective factors. It was hypothesized that when accounting for sociodemographic factors and trauma exposure AI would display equivalent rates of suicide risk and substance use disorders as non-Hispanic White (NHW) participants. Furthermore, among the AI sample it was expected that individuals with no SR would demonstrate greater activity in dorsolateral prefrontal cortex and inferior frontal gyrus as compared with individuals with SR when engaging inhibitory control.

Methods: Participants were drawn from the first 500 individuals recruited for the Tulsa-1000 (T1000), a naturalistic longitudinal study of 1000 people aged 18-55 (n = 476 with stop-signal task data). We employed propensity matching analysis to generate a matched sample of AI (n = 76) and NHW participants (n = 76) with respect to biological sex, age, education, income, reading ability, and trauma exposure. We then compared these groups on prevalence of suicide risk versus no suicide risk as indicated on clinician administered interview. Among the AI subsample, we then examined blood oxygen level dependent (BOLD) signal during a functional Magnetic Resonance Imaging (fMRI) scan during completion of the stop-signal task. Response inhibition was defined as the contrast of percent signal change during hard stop trials as compared to easy stop trials at a priori regions of interest (ROIs) drawn from original the SST development paper (dlPFC; IFG) and defined by the Brainnetome cytoarchitectural atlas. Whole brain analyses were also conducted by adding SR into the linear mixed effect model used to extract BOLD signal and using conservative voxel-wise correction (p < 0.005) and auto-correlation function values for cluster size correction.

Results: Following the propensity matching procedure groups did not differ on the matching variables (p’s 0.56-0.98). Comparing the propensity matched groups, the AI sample displayed lower occurrence of SR (29%) relative to the NHW participants (53%), χ2 = 8.77, p = 0.003, OR = 0.37). With respect to neuroimaging results for the a priori ROI analyses among AI individuals those without SR demonstrated increased activation in the left dlPFC (t(54.2) = 2.19, p = 0.03) and IFG (t(51.97) = 2.26, p = 0.03) in the hard versus easy contrast of the SST compared to those with no SR. Whole-brain linear mixed effects models maintained the effects related to SR indicating a significant cluster of increased activation in the dlPFC comprising 83 voxels with a center of mass at (-27.0, -45, 21).

Conclusions: Results indicate that (1) accounting for risk factors such as sociodemographic variables and trauma exposure the AI sample demonstrated lower levels of SR than NHW and (2) Among AI participants those with no SR showed higher levels of activity in executive control regions during the SST. These findings are a timely first step in examining SR is the AI population as AI demonstrated the largest increase in deaths by suicide of any racial group in the past decade. Results add to a burgeoning literature indicating the presence of protective factors among these communities and also that high prevalence rates of mental health difficulties may be largely driven by disproportionally high-risk burden within AI communities. The current study also posits inhibitory control as a potential neural mechanism underlying protective effect among AIs against suicide risk. These findings are limited in that they do not consider potential physical and mental health comorbidities. Furthermore, the parent data set for these secondary analyses did not include assessment of culturally specific risk and resilience variables for AI. Future research is needed to examine the specific factors related to mental health risk and protection among AIs. The current study provides an important first step towards culturally informed clinical neuroscience among AI populations.

Keywords: Inhibitory Control, Suicidality, Native Americans

Disclosure: Nothing to disclose.

P288. Clinical Outcome of Adolescents and Young Adults at Familial Risk for Bipolar Disorder

Gahan Pandina*, Wayne Drevets, Stephanie Rassnick, Solanki Bhavna, Carla Canuso, Mary Fristad, Christoph Correll, John Nurnberger, Manpreet Singh, Richard Weisler, Melvin McInnis, Sarah Atkinson, Mary Stedman, Fernando S. Goes, Louise Thurman, Stephen Strakowski, Tracy Greer, Andrew Nierenberg, Giacomo Salvadore, Melissa DelBello

Johnson and Johnson, Titusville, New Jersey, United States

Background: Bipolar disorder (BD) is highly familial. Studying offspring of parents with BD provides the opportunity to identify risk markers for illness development. Functional decline often predates BD illness and may be an early target for intervention. The Aretaeus Study was a 2-year, longitudinal observational study to assess psychosocial and biological predictors of emergent mood symptoms (depression, mania or hypomania) in youth offspring of a parent with BD. We hypothesized that functional impairment, prior to onset of any BD-spectrum diagnosis or clinical initiation of antipsychotics or mood stabilizers, would be predictive of clinical worsening or transition to BD-spectrum diagnosis.

Methods: Participants aged 15- 25 years with a biological parent with BD recruited from clinical and non-clinical settings were assessed every 3 months for up to 24 months. Volunteers were excluded if they had current or prior mood stabilizer or antipsychotic drug exposure, or a diagnosis of BD-spectrum disorders or psychosis. Global Assessment of Functioning (GAF) was assessed at all timepoints by trained clinicians using the modified GAF scale (Hall, 1995). Participants were stratified at screening by GAF as functionally impaired (GAF ≤ 70) or not impaired (GAF > 70). Clinical diagnostic and symptom rating scales assessed mania and depression symptoms using the Longitudinal Interval Follow-Up Evaluation (LIFE) Psychiatric Status Rating (PSR) score for DSM-IV-TR psychiatric disorders, the Bipolar Prodrome Symptom Scale – Full Prospective (BPSS-FP), and the General Behavioral Inventory. Participant-reported outcomes of depression, mania, sleep, anxiety, and social functioning were measured at regular intervals via a smart-phone app. Treatment was administered as deemed necessary by the participant’s treating clinician without restriction.

Results: Participants (N = 223) were recruited at 17 US-based sites; 84 (37.7%) were in the Low GAF group and 149 (62.3%) were in the High GAF group. A majority (70%) completed the study, though significantly fewer Low vs. High functioning participants were study completers (59.5% vs. 76.3%; p = 0.008). The Low GAF group was younger (17.9 years vs. 19.3 years; p < 0.001) included slightly more females (66.7% vs. 59.0%; p = 0.253), but had similar race / ethnicity composition compared with the high GAF group (82% White and 90% Not Hispanic/Latino vs. 79% White and 86% Not Hispanic/Latino).

Low (vs. High) GAF participants had more frequent prior antidepressant (32% vs. 17%) and anxiolytic use (6% vs. 1%) at baseline. Proportion of weeks in the 6 months prior to baseline with clinically relevant symptoms of a Major Depressive Episode on the LIFE (PSR score >3) was greater for the Low vs. High GAF group (28%+38 vs. 6%+18, p < 0.001). The proportion of weeks during the 6 months prior to baseline with Mania/Hypomania symptoms was comparable between groups (Low GAF = 0.4%+3.3 vs. High GAF 0.8%+5.8, p = 0.405). Low (vs. High) GAF participants had more severe baseline BPSS-FP Index scores for both Mania (9.3 + 9.0 vs.3.9 + 5.4) and Depression (20.7 + 14.9 vs. 9.0 + 12.7). Participant reported outcomes of depression and anxiety, but not mania, were worse at baseline in the Low vs High GAF group; depression – Quick Inventory of Depressive Symptoms-16 (8.4 + 5.1 vs. 4.3 + 3.4), anxiety - General Anxiety Disorder-7 (6.4 + 5.3 vs. 2.5 + 3.2), and manic symptoms - Altman Self-Rating Mania (2.4 + 2.6 vs. 1.6 + 2.2).

Over the 2-year post-baseline period, the Low GAF group was twice as likely as the High GAF group to start a new psychotropic medication (36.9% vs. 17.3%), significantly higher for antidepressants (32.1% vs. 16.5%; p = 0.007) and a trend in difference for anxiolytics (6.0% vs. 1.4%; p = 0.061): the Low GAF group was significantly more likely to require a dose increase (16.7% vs. 5.0%; p = 0.004). Adverse events over 2 years were comparable in Low and High GAF groups (47 % vs. 49%), as were psychiatric AEs (13% vs. 10%). Serious psychiatric AEs were higher in Low versus High GAF group: there were 5 suicide attempts in the Low GAF group and none in the High GAF group.

Prospective 2-year data on the LIFE PSR score paralleled baseline differences: proportion of weeks with PSR scores >3 for Major Depressive Episode were significantly greater (p = 0.008 in the Low (29.3%+35) vs. High GAF group (10.7%+20). Both groups had a low proportion of weeks with PSR score >3 for mania/hypomania. There was a trend for worsening of depression symptoms in the High, but not the Low GAF group based on change from baseline for proportion of weeks with PSR scores >3 (4.7 vs. 1.3, p = 0.232).

Conclusions: Prospective longitudinal data of youth at familial risk for BD showed that a high level of functional impairment at baseline was associated with greater expression of symptoms of depression, anxiety, and manic symptoms. Baseline functional impairment was associated with higher psychotropic medication use and more dose increases over two years of prospective observation. Participants with higher functioning worsened over two years in clinical symptoms, but never reached the level of symptoms of the group with low functioning at baseline, which continued to show high levels of depressive symptoms over 2 years. Functional impairment in youth at familial risk for BD appears to be strongly associated with long-term, clinically significant mood symptoms, especially depression, requiring intervention. Longer-term risk for BD requires further study.

Keywords: Bipolar Disorder, Familial Risk of Bipolar Disorder, Early Identification of Risk, Childhood Onset Bipolar Disorder, Clinical Heterogeneity

Disclosure: Janssen Research and Development, LLC: Employee (Self)

Johnson and Johnson: Stock / Equity (Self)

P289. Antidepressant Response of Electroconvulsive Therapy and Magnetic Seizure Therapy: Response Trajectories by Symptom Clusters

Zhi-De Deng*, Shawn McClintock, Mustafa Husain, Sarah Lisanby

National Institute of Mental Health, Bethesda, Maryland, United States

Background: Electroconvulsive therapy (ECT) is a highly effective treatment for severe depression, particularly for cases with psychotic features, treatment-resistance, and acute suicidality. Magnetic seizure therapy (MST), in which seizures are induced using high-dose repetitive transcranial magnetic stimulation, can potentially offer similar efficacy as ECT, but with fewer adverse side effects. Although the efficacy rates between the two treatment modalities have been shown to be relatively similar, it is unclear whether they differentially act on depressive symptom dimensions and clusters.

Methods: This was a secondary analysis of a double-blind, randomized, controlled trial comparing the efficacy of ECT (ultrabrief pulse, right unilateral electrode placement) and MST (circular coil over vertex). The randomized clinical trial was conducted under an Investigational Device Exemption from the US FDA and was approved by the Institutional Review Boards of the New York State Psychiatric Institute, Duke University Medical Center, and UT Southwestern Medical Center. Participants were referred for treatment with ECT, between the ages of 21 and 81, and met DSM-IV-TR criteria for a major depressive episode in the context of major depressive disorder or bipolar depression based on the Structured Clinical Interview for Diagnosis, and had a baseline 24-item Hamilton Depression Rating Scale (HAMD) total score of 18 or greater. Exclusion criteria included a history of neurological disorders, head trauma, contraindications to transcranial magnetic stimulation, current unstable or serious medical illness, pregnancy, presence of implanted electronic devices, history of ECT in the prior six months or failure to previously respond to ECT, or a Mini Mental Status Exam total score less than 24. Data from an intent-to-treat sample of 72 participants were included in this analysis.

First, we conducted an exploratory factor analysis of HAMD subitems at baseline. All but one participant scored 0 on the item Insight; therefore, we removed this item from the factor analysis (thus the HAMD now comprised 23 items). The number of factors was determined using parallel analysis. The minimum residual approach was used with oblique, oblimin rotations to allow for between-factor correlations. Items with loadings > = 0.3 were included for each factor. The factor scores at each treatment, calculated as the sum of individual item scores at each treatment, were normalized to baseline factor scores.

Next, we performed latent class trajectory modeling to classify participants into classes based on fitting heterogeneous longitudinal polynomial response trajectories. We used the 24-item HAMD total score at each treatment for up to the eighth treatment, from a subset of 67 participants who had received a minimum of three ECT or MST treatments. We used a model with up to a cubic polynomial term, with quadratic random effects and a proportionality constraint to allow variance structures to vary across classes. To assess model adequacy, we calculated the average posterior probability of class membership (>0.7 in all classes is regarded as acceptable). We further assess model adequacy using odds of correct classification (>5 recommended) and mismatch (close of zero recommended). Finally, we explored whether baseline clinical, demographic characteristics, and treatment modalities were associated with response trajectories.

Results: For the baseline 23-item HAMD, the Kaiser–Meyer–Olkin sampling adequacy measure was 0.58, which was minimally adequate for factor analysis. The 23 items loaded onto 4 factors. Factor 1 consisted of hopelessness (loading score = 0.77), depressed mood (0.61), work and activities (0.56), helplessness (0.53), worthlessness (0.44), psychic anxiety (0.40), and suicide (0.34); Factor 2 consisted of late insomnia (0.76), general somatic symptoms (0.34), psychomotor retardation (0.34), and early insomnia (0.30); Factor 3 consisted of weight loss (0.60), gastro-intestinal symptoms (0.56), hypochondriasis (0.53), and somatic anxiety (0.43); Factor 4 consisted of middle insomnia (0.70), guilt (0.64), and depersonalization (0.34). Over the first 8 treatments of ECT or MST, Factors 1 and 4 showed substantial reductions relative to baseline (z-scores~-1.5 at treatment 8), whereas Factors 2 and 3 only slight reductions (z-score > -1). There was no difference between ECT and MST on the magnitude or speed of symptom factor score reduction.

In the 3-class model, the response trajectories showed distinct temporal patterns. The first class, which we labeled “nonresponse” (N = 10, 14.9%), showed minimum HAMD reduction over the eight treatments. The second class, labeled as “linear response” (N = 46, 68.7%), showed steady linear reduction in HAMD. The third class, labeled as “rapid response” (N = 11, 16.4%), showed maximal HAMD reduction within the first three treatments. Further exploratory analysis showed that the three classes did not differ in baseline depression severity (symptom factor scores, or total HAMD), age, sex, or treatment modality.

Conclusions: ECT and MST did not differ in their impact on symptom dimensions or the speed of symptom improvement. The most significant improvements observed were in the core mood symptoms of depression. We identified distinct classes of response trajectories. Future work is needed to identify predictors of response class using discrimination analysis with additional psychosocial and physiological covariates.

Keywords: Electroconvulsive Therapy, Magnetic Seizure Therapy, Factor Analysis, Latent Class Analysis

Disclosure: Nothing to disclose.

P290. Identification of BNST Gene Networks Modulating Susceptibility and Resilience to Chronic Stress Using Single-Nucleus RNA Sequencing

Nikolaos Daskalakis, Christos Chatzinakos, Max Pöhlmann, Claudia Klengel, Kenneth McCullough, Emily Newman, Nina Dedic, Robert Fenster, Torsten Klengel, Mathias V Schmidt, Kerry Ressler, Jakob Hartmann*

McLean Hospital, Harvard Medical School, Belmont, Massachusetts, United States

Background: Mood and anxiety disorders can develop as a result of the interaction between genetic predispositions and environmental risk such as traumatic and/or chronic stress. As with other complex illnesses, there is no universal susceptibility gene for such disorders. Instead, multiple genes with small effect sizes may contribute to the disease phenotypes. Moreover, only a subset of individuals is susceptible to stress and/or trauma, while many others show a remarkable resilience to adverse experiences. Although the bed nucleus of the stria terminalis (BNST) plays an important role in the stress response and emotional and social behaviors, it has been largely overlooked with respect to its possible dysregulation in mental disorders. In this study we aimed to investigate the polygenic architecture of stress susceptibility and resilience within the BNST at the single cell level relevant to mood and anxiety disorders.

Methods: In an unbiased approach, we performed single-nucleus RNA sequencing (snRNAseq) using the inDrops technique to identify distinct neuronal subpopulations within the BNST that demonstrate resilient-specific or susceptible-specific transcriptional changes following chronic social defeat stress (CSDS) in mice. Historically, the classification of defeated mice into susceptible and resilient groups has been based on their performances in a social avoidance task. However, CSDS also leads to multiple other behavioral and physiological changes reminiscent of depressive- and anxiety-like symptoms in a subset of mice. In the past, such readouts have often been neglected in the classification of stress-resilient and stress-susceptible mice. To address these limitations, we subjected C57BL/6J male mice (n = 56) to a 3-week CSDS paradigm and developed a comprehensive testing battery for the characterization of CSDS-induced behavioral and physiological alterations.

Results: In the majority of animals CSDS induced not only a social avoidance phenotype, but also increased anxiety-related behavior as well as critical changes in physiological readouts relevant to HPA axis activity (social avoidance test: social interaction ratio, t54 = 1.825, p = 0.07; open field test: total distance, t54 = 5.191, p < 0.0001; elevated plus maze: number of open arm entries, t54 = 2.005, p < 0.05; baseline corticosterone: t54 = 2.570, p < 0.01). Thus, the classification into defeat-resilient and defeat-susceptible mice was based on the principal component analysis of 20 different behavioral and physiological readouts. 24 hrs after the last defeat, mice were sacrificed and BNST tissue punches of 2-4 animals of the same group were pooled based on the k-means clustering method. This resulted in 17 sample pools (n = 5 ctrl; n = 4 defeat resilient; n = 8 defeat susceptible) for subsequent snRNAseq. After applying QC metrics, we profiled transcriptomes of > 100.000 nuclei across all samples. We have identified 33 cell clusters, annotated into 5 major cell types of inhibitory neurons, excitatory neurons, astrocytes, microglia and oligodendrocytes. Many of these clusters express known markers of the BNST such as Sst, Tac2, Npy or Adcyap1. We have also identified populations of neurons with previously undescribed molecular signatures. In order to identify distinct neuronal subpopulations that demonstrate resilient-specific or susceptible-specific transcriptional profiles, we are currently performing differentially gene expression as well as pathway analyses of ctrl, defeat-resilient and defeat-susceptible samples with the goal to distinguish mechanisms related to stress exposure from those related to susceptibility and resilience.

Conclusions: We provide initial data that will aid in the construction of a comprehensive map of resilient-specific and susceptible-specific cell-types within the mouse BNST. To this end, we have identified both known and previously uncharacterized cell-types within the BNST. Follow up studies will assess the functional role of these cell-types in stress susceptibility and resilience.

Keywords: BNST, Single-Cell RNA Sequencing, Chronic Social Defeat, Stress Resilience and Susceptibility

Disclosure: Nothing to disclose.

P291. Transdiagnostic Prediction of Depression and Cognition Using fMRI and PET

Sophie Holmes*, Xilin Shen, Ryan Cool, Margaret Davis, Todd Constable, Irina Esterlis

Yale University, New Haven, Connecticut, United States

Background: Depression and cognitive dysfunction occur across psychiatric disorders and may have shared neurobiological underpinnings that could be targeted in a symptom- rather than disorder-specific manner. Disturbances in functional networks and the glutamate system are evident across major depressive disorder (MDD), posttraumatic stress disorder (PTSD) and bipolar disorder (BD). Investigating both network organization and the glutamate system as they relate to shared symptoms transdiagnostically will provide a more complete mechanistic understanding of transdiagnostic symptoms and could reveal novel treatment targets.

Methods: A transdiagnostic sample of 85 individuals were imaged with fMRI and [18F]FPEB PET to identify network organization and availability of the glutamate receptor mGluR5 (n = 32 MDD; n = 24 PTSD; n = 29 BD). Connectome-based predictive modeling (CPM) was applied to the fMRI data. Specifically, CPM with leave-one-out cross validation was used to identify functional connections (‘edges’) within a 268-node matrix that predicted depression severity and delayed recall memory transdiagnostically. Mean [18F]FPEB (VT) values from each of the 268 nodes were also correlated with the behavioral score for each participant.

Results: CPM successfully predicted depression severity and delayed recall memory across MDD, PTSD and BD individuals, as indicated by a significant correspondence between actual and predicted behavioral values (depression: r = 0.25, p = 0.02, n = 85; delayed recall: r = 0.34, p = 0.02, n = 55). Connections within and between medial-frontal, fronto-parietal and default-mode networks, predicted depression severity; and connections within and between dorsal attention, ventral attention and fronto-parietal networks were predictive of delayed recall. Successful prediction and a similar pattern of results was also observed when including healthy controls (n = 35; total n = 90). PET results revealed significant negative correlations between mGluR5 availability and depression severity in nodes of the PFC and cerebellum, transdiagnostically. Positive correlations were observed between mGluR5 and delayed recall in nodes of the PFC and parietal regions (p’s < 0.05).

Conclusions: We were able to generate transdiagnostic predictive models of depression severity and delayed recall memory, pointing to shared mechanisms underlying these constructs across MDD, PTSD and BD. We also demonstrate associations between mGluR5 availability and depression severity/cognition. Brain-behavior relationships observed with both fMRI and PET converged on regions of the PFC. Our findings implicate distinct transdiagnostic networks underlying depression and delayed recall memory – networks that can be targeted with novel symptom-specific treatment interventions. Next steps will be to fuse fMRI and PET data and determine whether the observed predictive functional networks are underpinned by regional alterations in mGluR5 availability.

Keywords: Depression, fMRI, PET

Disclosure: Nothing to disclose.

P292. Tianeptine, but not Fluoxetine, Decreases Avoidant Behavior in a Mouse Model of Early Developmental Exposure to Fluoxetine

Elizabeth Pekarskaya, Emma Holt, Jay Gingrich, Mark Ansorge, Jonathan Javitch, Sarah Canetta*

Columbia University, New York, New York, United States

Background: Depression and anxiety, two of the most common mental health disorders, share common symptoms and treatments. Most pharmacological agents available to treat these disorders target monoamine systems. Currently, finding the most effective treatment for an individual is a process of trial and error. To better understand how disease etiology may predict treatment response, we studied mice exposed to the selective serotonin reuptake inhibitor (SSRI) fluoxetine (FLX) during early development. These mice are known to show the murine equivalent of anxiety- and depression-like symptoms in adulthood, and here we report that these mice are also behaviorally resistant to the antidepressant-like effects of adult SSRI administration. The atypical antidepressant tianeptine (TIA) exerts its therapeutic effects through agonism of the mu-opioid receptor instead of directly targeting monoaminergic systems. Here, we investigated whether TIA administration in adulthood would be effective in this early developmental FLX exposure model of SSRI resistance.

Methods: C57BL/6J (C57) male and female pups were injected with either FLX (10 mg/kg, i.p) (n = 39, 18 male, 21 female) or vehicle (n = 31, 14 male, 17 female) from postnatal (PN) day 2 to 11, a period in which mouse brain development parallels that of the third trimester of a human pregnancy. Avoidant behavior was measured in postnatal FLX (PN FLX) or vehicle (PN VEH) exposed mice in adulthood in the open field test (OF). Cages with co-housed PN FLX and PN VEH mice were subsequently pseudorandomly organized to receive either chronic FLX or vehicle control administered as adults. FLX (18 mg/kg) was administered through the drinking water for three weeks; the vehicle control group received water alone. Behavioral testing in the OF and novelty suppressed feeding task (NSF) began after three weeks of FLX administration, which continued to be administered during testing. A two-week washout period followed completion of post-FLX behavioral testing before beginning TIA administration. Cages were again pseudorandomly reorganized into TIA and vehicle control administration groups, ensuring equal distribution of those which had received FLX or vehicle during the first drug administration period. A 30 mg/kg solution of TIA NaCl (Qingdao Sigma Chemical Co., purity verified by NMR analysis) was delivered at a dose of 0.1 ml/10 grams mouse weight via intraperitoneal injection twice per day for 14 days. TIA was dissolved in 0.9% sterile saline. The respective vehicle control group received injections of 0.9% sterile saline. The effects of chronic FLX treatment on adult PN FLX mice on a 129SvEv (129) background was also assessed using the NSF.

Results: We found that as adults, C57 PN FLX animals share a similar avoidant phenotype to that previously reported in 129 PN FLX mice, manifest as a decrease in rearing and center time in the OF relative to PN VEH mice (unpaired t-test, p < 0.005 and p = 0.049, respectively, n = 31 PN VEH, 39 PN FLX). Interestingly, we found that adult FLX administration did not improve, or even exacerbated, avoidant behavior in PN FLX mice. PN FLX mice that had received adult FLX administration showed decreased rearing (unpaired t-test, p = 0.02, n = 17 VEH, 20 FLX) and center time (unpaired t-test, p = 0.03, n = 17 VEH, 20 FLX) in the OF relative to PN FLX mice given vehicle (VEH), and no effect was seen on their latency to feed in the NSF (unpaired t-test, p = 0.70, n = 17 VEH, 20 FLX). Similarly, adult FLX administration increased latency to feed in the NSF in PN FLX on a 129 background (unpaired t-test, p = 0.04, n = 27 VEH, 30 FLX). By contrast, adult TIA administration increased rearing and center time in the OF in PN FLX mice relative to those treated with vehicle (unpaired t-test, p = 0.005 and p = 0.03, respectively, n = 19 VEH, 20 TIA). Adult TIA administration also decreased latency to feed in the NSF in PN FLX mice, relative to those receiving vehicle control (unpaired t-test, p = 0.0001, n = 17 VEH, 19 TIA).

Conclusions: Our results confirm prior work demonstrating that in mice exposure to FLX during early development produces an avoidant-like phenotype as adults. In a mouse, the brain development occurring during this period of exposure approximates the brain development occurring during the third trimester in a human. Consistent with this, human epidemiological data indicates that in utero exposure to FLX increases the risk of being diagnosed with an affective disorder in adolescence and adulthood. Our results now demonstrate that early exposure to FLX results in affective symptoms that are subsequently resistant to FLX administration in adulthood. Remarkably, the atypical antidepressant TIA remains completely effective in improving affective behaviors in these mice. Overall, these findings suggest that PN FLX mice may represent a model of SSRI-resistant affective behavioral changes and that TIA may be a promising alternative treatment from SSRIs for humans with suspected in utero early developmental exposure to SSRIs, and more broadly that it may be helpful in a subset of people with SSRI-resistant depression.

Keywords: Avoidance, Fluoxetine, Tianeptine, Mouse Models, Brain Development

Disclosure: Nothing to disclose.

P293. Mu Opioid Receptor Signaling is Required for the Cellular Effects of Ketamine Enantiomers in the Lateral Habenula

Joshua Chandra, Aubrey Siebels, Pablo E. Castillo, Roberto Malinow, Matthew Klein*

Depression and Anxiety Center, Icahn School of Medicine at Mount Sinai, New York, New York, United States

Background: Racemic ketamine [(R,S)-ketamine] as well as esketamine [(S)-ketamine] are potent N-methyl-D-aspartate receptor (NMDAR) antagonists that are increasingly used in the clinical treatment of refractory depression. The enantiomer arketmaine [(R)-ketamine] has also demonstrated antidepressant properties in both preclinical and clinical studies. Both enantiomers display activity at a number of neuronal receptors, including μ-opioid receptors (MORs), complicating the issue of mechanism of action. Preclinical studies have linked the antidepressant effect of racemic ketamine to its ability to reduce hyperactivity in the lateral habenula (LHb), a brain nucleus involved in reward learning. We recently demonstrated that intact MOR signaling is required for the antidepressant actions of (R,S)-ketamine in rodents displaying LHb hyperactivity, a preclinical model of depression. The potency of the ketamine enantiomers to decrease LHb hyperactivity, and the requirements of MOR signaling are currently unknown. Increasing our understanding of the mechanism of action of ketamine enantiomers in reducing LHb hyperactivity may help in the development of new rapid antidepressant compounds.

Methods: We prepared acute LHb brain slices from two different rodent models of depression– congenital learned helplessness (cLH) and acquired learned helplessness (aLH)–and used calcium imaging to test the cellular effects of co-administration of ketamine enantiomers and MOR antagonists on neuronal activity.

Results: We find that acute application of either ketamine enantiomer results in a similar reduction of LHb activity in our rodent models, that is reduced by co-application of the MOR antagonist CTAP. The NMDAR antagonist APV occludes the ability of (S)-ketamine, but not (R)-ketamine, to reduce LHb activity.

Conclusions: Our results suggest that intact MOR signaling is required for the ability of ketamine enantiomers to acutely reduce LHb neuronal activity. However, (S)-ketamine, but not (R)-ketamine, also requires intact NMDAR signaling as well. These findings suggest that the two ketamine enantiomers may have different mechanisms of action for their antidepressant effects, and that future studies of the relative contributions of NMDAR and MOR signaling to rapid antidepressant effects is warranted.

Keywords: Ketamine, Lateral Habenula, Molecular Neuroscience

Disclosure: Nothing to disclose.

P294. Early Life Stress Induces Amotivation and Alters Epigenetic Regulation in the Nucleus Accumbens in a Sex-Dependent Manner

Alexia Williams*, Charlotte Bavley, Reza Karbalaei, Evelyn Ordones Sanchez, James Flowers II, Kennedy Coates, Atiba Ingram, Benjamin Garcia, Deena Walker, Mathieu Wimmer, Debra Bangasser

Temple University, Philadelphia, Pennsylvania, United States

Background: Although many pharmaceutical therapies have been developed for treating mood disorders, over half of individuals that seek treatment do not respond positively, indicating a dire need for new treatments and thus a need for uncovering novel molecular mechanisms underlying stress-induced behaviors. Early life stress (ELS) is a well-known risk factor for the development of several psychiatric illnesses, including depression. Molecular studies on the impact of ELS on the brain have primarily focused on cognition-related brain regions and behavior, so the molecular mechanisms underlying the impact of ELS on reward-related regions, such as the nucleus accumbens (NAc), and motivated behaviors are lacking.

Here we used the Limited Bedding and Nesting (LBN) model, which consists of rearing pups in an impoverished environment during early life (PND 2-9), to assess the effects of ELS on motivated behaviors and on transcriptional and post-translational regulation in the NAc, a key region involved in depression-like phenotypes such as reduced motivation and anhedonia. In a previously published dataset we found that LBN promotes sex-specific differential expression in the NAc. Remodeling of unique histone marks may contribute to this, so in this study we performed a genome-wide screen of posttranslational histone modifications (PTM) in the NAc to assess whether epigenetic mechanisms contribute to these distinct transcriptional profiles. We also performed pathway analyses on our RNAseq dataset to identify unique upstream regulators and pathways being significantly enriched by LBN. Additionally, in our last experiment we test for the effects of LBN on motivation for male and female Long-Evans rats to access a palatable food reward using an operant self-administration task.

Methods: Experiment 1: Pups were reared in either a LBN or standard environment during PND 2-9. Nuclei were isolated from NAc punches from LBN or control adult males and females (n = 4-5/group) and histones were extracted. Propionic anhydride derivatization of histones and peptide extraction and subsequent global histone posttranslational modification analysis was performed.

Experiment 2: Qiagen Ingenuity Pathway Analysis (IPA) was performed on our previously published NAc RNAseq data set that included LBN and control males and females (n = 4-6/group) in order to assess sex differences in the effects of LBN on upstream regulators and enriched pathways in the NAc.

Experiment 3: Pups were reared in either a LBN or control environment (n = 4-11/group) during PND 2-9. At PND 60 rats were run through a self-administration operant task where they lever pressed for sucrose pellets over the course of 13 days (10 days training on FR1; 1 day on a progressive ratio task (PR); 1 day FR1; 1 day PR).

Statistical analysis: Exp. 1: Relative abundance of histone PTMs were calculated and PTM analysis was performed. Exp. 2: Qiagen IPA was used to assess LBN effects on upstream regulators and pathway enrichment. Exp. 3: data was normalized when appropriate followed by ANOVA testing and pairwise comparison post-hoc analyses.

Results: Our genome-wide assessment of histone PTMs revealed differing patterns of LBN-driven PTMs in the NAc of males and females (group N’s = 4-5). We found that LBN significantly increased the expression of 3 histone marks in males (H3K4me3, H4K12ac, H3K18acK23ac) and decreased the expression of 1 histone mark in females (H2A1K5acK9ac) (p’s < 0.05).

Using IPA we identified a sex difference in several predicted upstream regulators in our previously published LBN NAc RNAseq dataset. Notably, CREB1 was significantly enriched as an upstream regulator in LBN females. Additionally, IPA identified CREB signaling as a significantly enriched pathway in stressed females. Targets of this upstream regulator also differed between sexes. In females, CREB1 is a predicted regulator of 24 differentially expressed genes (DEG), of which 10 are activated and 14 are inhibited. In males, CREB1 is a predicted regulator of 6 DEGs, where 5 are activated and 1 is inhibited.

Preliminary data from an ongoing study shows that LBN reduces motivation for a food reward in a PR operant task in non-food deprived adult male and female Long-Evans rats (p = 0.025). Further analyses of our preliminary data using an FR1 schedule show a significant interaction effect between sex and stress (p = 0.045). Pairwise comparison analyses show that LBN females lever press less on an FR1 schedule compared to LBN males by the last day of testing (p = 0.005).

Conclusions: Our results identify two potential molecular mechanisms in the NAc that may drive our observed sex-specific LBN-induced phenotypes: sex-specific histone modifications and sex-specific enrichment of upstream regulators, such as CREB1. Acetylation of two of our identified histone marks (H4k12ac and Hk23ac) has been shown to be in part driven by CREB-binding protein (CBP). Previous work shows that acetylation of these histone marks in reward-related regions is altered by adult social stress models in rats. Taken together this suggests that CREB signaling and CBP-driven histone acetylation may be a driving force of stress phenotypes. In an ongoing preliminary study, we are finding that LBN reduces motivation to lever press for a food reward. Upcoming studies will assess the effects of LBN on motivation for other natural rewards, such as social rewards, as well as the role epigenetic modifications, such as CBP-driven histone acetylation, may be playing in these LBN-driven depression-like phenotypes.

Keywords: Early Life Stress, Nucleus Accumbens, Motivation, Epigenetics, Sex Differences

Disclosure: Nothing to disclose.

P295. Sidekick-1, A Novel Regulator of Stress Resilience in the Prefrontal Cortex

Vedrana Cvetkovska*, Pedro do Couto Bordignon, Joëlle Lopez, Emily Cha, Rosemary C Bagot

McGill University, Montreal, Canada

Background: Depression is a leading cause of disability worldwide. Stress is a major risk factor, yet some individuals are resilient to stress. Both environmental and genetic factors contribute to the dysregulation of neural circuits in depression and genes that regulate the formation, maintenance, and plasticity of synapses are of particular interest as molecular hubs for regulation of circuit function.

We previously identified Sidekick-1 (Sdk1) as an affective circuit hub gene in a network regulating stress resilience. Overexpression of Sdk1 in the prefrontal cortex (PFC) increased resilience to stress in male mice. Separately, several genome-wide association studies in humans found SDK1 variants associated with depression, suggesting an evolutionarily conserved role in regulation of emotional behavior.

Sdk1 is a cell surface molecule implicated in circuit formation in the retina. However, little is known about cell-specific expression patterns of Sdk1 in the adult brain and its function within affective circuits. Here we probe Sdk1 cell-type and layer-specific expression in the PFC, conservation between mice and humans, and its modulation by stress in both male and female mice.

Methods: Chronic social defeat stress generated resilient and susceptible phenotypes in 10 week old male mice (n = 12 control, n = 11 stress), and subchronic variable stress generated a susceptible phenotype in 10 week old female mice (n = 10 control, n = 10 stress). Depression-like behavior was assessed using social interaction and social preference tests. Quantitative real-time PCR determined bulk Sdk1 expression levels in the PFC, nucleus accumbens (NAc) and ventral hippocampus of control and stressed animals. The expression pattern of Sdk1 mRNA in the PFC of 10 week old mice (n = 14) was assessed using multiplex RNAScope fluorescent in situ hybridization. Probes for Slc17a7 (vGlut1) and Slc32a1 (vGAT) identified excitatory and inhibitory neurons, respectively. PFC layers 1, 2/3, 5 and 6 were designated by distance from the midline. PFC-NAc neurons were retrogradely labeled with AAVrg-Cre-EGFP injected into the NAc, and the PFC was immunostained for GFP and in situ hybridized for Sdk1. Publicly available scRNAseq datasets (Allen Brain Map) from mouse and human whole cortex were used to identify cell-type specific expression of Sdk1 and de novo clustering on sub-regions was performed using Seurat.

Results: We found that Sdk1 is expressed in the PFC, NAc and ventral hippocampus of adult male and female mice, with expression highest in the PFC. qPCR revealed a significant reduction in Sdk1 expression in the PFC of stressed susceptible male (p < 0.01) and female mice (p < 0.05). Given the role of the PFC-NAc pathway in stress resilience, we probed correlations in Sdk1 expression between the two regions, identifying a trending positive correlation in resilient male mice (r2 = 0.52 p = 0.07).

RNAScope in situ hybridization in the PFC showed that Sdk1 was expressed in 50.9% of vGlut1-positive neurons and 37.5% of vGAT-positive neurons. The highest level of Sdk1 expression was observed in layer 6 (55.7%, p < 0.0001) with moderate expression in layers 2/3 (17.4%) and 5 (23.4%). Patterns of cell-type and layer-specific Sdk1 expression were conserved in scRNAseq analysis of human PFC. De novo clustering of scRNAseq data from mouse PFC showed that Sdk1-expressing cells were found across clusters, with several clusters of excitatory or inhibitory neurons marked by high numbers of Sdk1-expressing cells. Retrograde GFP labeling of PFC-NAc projection neurons and combined in situ hybridization for Sdk1 and immunohistochemistry for GFP showed that a subpopulation of NAc projecting neurons in the PFC express Sdk1.

Conclusions: In this study we characterized the prefrontal expression of Sdk1, a novel regulator of stress resilience. We found that Sdk1 is modulated by stress in male and female mice and is expressed in subsets of both excitatory and inhibitory neurons, with a significant enrichment in deep layers of the PFC. Cell-type and cortical layer specificity was conserved between mice and humans. In addition to regulation of absolute expression in the PFC, coordinated regulation of Sdk1 expression across brain circuits may underlie resilience. Future work will address the circuit-specific effects of Sdk1 in behavioral adaptation to stress. As a cell surface receptor, Sdk1 is a potential target for pharmacological intervention. Understanding how Sdk1 confers resilience may lead to development of new mechanistically-informed treatments for depression.

Keywords: Prefrontal Cortex, Depression, Stress Resilience, Mouse Models

Disclosure: Nothing to disclose.

P296. Combined Effects of Nitric Oxidase Synthetase Intron Polymorphism and Childhood Emotional Abuse on the High-Risk Suicide Attempter Phenotype

Aiste Lengvenyte*, Emilie Olié, Robertas Strumila, Ryad Tamouza, Marion Leboyer, Philippe Courtet

CHU Montpellier, Montpellier, France

Background: Both genetic susceptibility and adversity in early age have been associated with the earlier onset and more severe course of suicidal behaviors. Early life adversity, especially emotional abuse has been shown to impair stress response system and cause oxidative stress. Nitrous oxide is involved in dopaminergic function modulation, and long-term memory formation, among other function. Several polymorphisms of nitric oxide synthase (NOS) genes have been associated with depression, suicide attempt (SA), though results remain inconclusive. Recent randomized trials also propose a rapid antidepressive effect of nitrous oxide, which is a donor for nitric oxide (NO), a final NOS product. Meanwhile, NOS3-knockout mice have diminished neurogenesis, impaired learning process, and show depressive-like behaviors. Stress has also been shown to rapidly increase NOS activity, possibly resulting in adequate memory consolidation, which is important for development of future response schemas. In the present study, we hypothesized that individuals with childhood adversity history and NOS polymorphisms might engage in suicidal behaviors at younger age, and more frequently.

Methods: We evaluated N = 501 individuals with SA history for their sociodemographic characteristics, childhood adversity using the Childhood Trauma Questionnaire (CTQ), as well as their clinical characteristics, including mental disorders according to the Mini International Neuropsychiatric Interview (MINI) screening tool, family history of mental disorders and suicide, and the characteristics of suicidal behaviors (age of first suicide attempt, number and severity of attempts). All individuals were also genotyped for the major nitric oxide synthetase 2 and 3 (NOS2 and NOS3). First, we compared all included characteristics according to the early-attempter cut-off set at 18 years age using the t-test, chi-square and appropriate nonparametric tests. Then, we performed haplotype analysis and analysis based on specific polymorphisms. Since childhood emotional abuse drove the association between childhood abuse and early suicidal behavior, and the 27-bp repeat polymorphism of NOS3 was the only genetic association, we the divided patients to four groups of either both positive, one positive, and one negative. We then performed a Cox-regression to see how these four groups differ. Finally, we applied several logistic regression models, controlling for covariates to see the independency of the associations. Level of significance was set at p < .05.

Results: Female sex, family history of mental disorders, CTQ total score, emotional abuse (strongest association), physical abuse, and sexual abuse, multi-attempter phenotype, severe SA history and the 27-bp repeat polymorphism of NOS3 were all statistically significantly associated with the early SA. Haplotype analysis revealed that associations were driven by the 27-bp repeat polymorphism of NOS3. When divided in four groups, we found that individuals with both childhood emotional abuse and the 27-bp repeat polymorphism of NOS3 were younger at their first SA (27.39 ± 13.21 vs 35.75 ± 16.07, p < .001), had more SA (31.6% vs 11.3%, p < .001), had more family history of SA (66.0% vs 39.3%, p < .001), and were more likely to have realized severe SA (30.2% vs 14%, p < .05) than those neither with the polymorphism nor with the emotional abuse history. Furthermore, those with either emotional abuse history or the 27-bp repeat polymorphism of NOS3 showed intermediate results. Cox regression confirmed the different distribution of the age of the first SA in four groups. Regression model showed that the effect was additive rather than synergistic. The model which included all associated factors with the age of the first SA (excluding CTQ total score and other substitutes due to their interaction with emotional abuse) had adjusted R2 of .130. It showed that emotional abuse, the 27-bp repeat polymorphism of NOS3, eating disorder history, and substance use disorder remained significantly independently associated with earlier age of the first SA (p < .05 in all cases).

Conclusions: Both reported emotional abuse and the 27-bp repeat polymorphism of NOS3 were associated with earlier age of the first suicide attempt in suicide attempters. These factors seem to have additive rather than interactive effect, and are also associated with a generally riskier phenotype with higher number of suicide attempts, family history of suicidal behaviors, and severe suicide attempt history. Further studies are needed to elucidate the mechanism of the presented associations, possibly targeting on the role of oxidative stress in the emergence of suicidal behaviors.

Keywords: Suicidal Behavior, Nitric Oxide, Childhood Adversity

Disclosure: Nothing to disclose.

P297. Anti-Cardiolipin Antibody: A Potential Biomarker for Depression

Renzo Costa*, Evangelia Fatourou, Debra Hoppenstaed, Jawed Fareed, Angelos Halaris

Loyola University Chicago Stritch School of Medicine, Chicago, Illinois, United States

Background: Remission rates for Major Depressive Disorder (MDD) are estimated to hover around 35% and about one-third of MDD patients fail to respond to conventional antidepressants. This is not surprising, as we have yet to identify the biological underpinnings of this psychiatric disorder. A promising avenue of exploration is the role of inflammation in depression, or at least in a subset of depressed patients. It is crucial to first establish which specific inflammatory biomarkers play a role in MDD’s etiopathology. CRP, IL-1β, IL-6, and TNF are strong contenders. Anti-cardiolipin antibody (aCL IgM) is an inflammatory marker that has the potential to be a robust candidate but there are insufficient studies to confirm this potential. Cardiolipin is a phospholipid, which is a class of molecules important for neurotransmitter signal conduction and neurodevelopment. Abnormalities in phospholipid regulation, as seen in antiphospholipid syndrome (APS), typically lead to hypercoagulable sequalae, but there is a growing body of evidence demonstrating neuropsychiatric repercussions. APS patients have higher depressive symptoms and, inversely, depressed patients have higher antiphospholipid antibodies titers than healthy controls.

Our study focused on aCL IgM. The primary goals were to investigate the longitudinal progression of aCL IgM in MDD subjects receiving antidepressant therapy in comparison to healthy controls and to determine if changes in aCL IgM correlate to changes in depressive symptoms. Our secondary goal was to ascertain if baseline aCL IgM could predict treatment response.

Methods: MDD subjects, both male and female between the ages of 20 – 65 years, had to be in either their first or recurrent episode of MDD and otherwise physically healthy.

Upon successful completion of a series of physiological and psychiatric screens, all subjects had their blood drawn for inflammatory biomarkers and completed a series of scales (the Hamilton Rating Scale for Depression (HAMD-17), Hamilton Rating Scale for Anxiety (HAM-A), and Beck Depression Inventory (BDI)) at a baseline visit.

MDD subjects were then enrolled in one of two treatment studies. Cohort-E received a 12-week regimen of escitalopram 20 – 40 mg/day (n = 20). Cohort-Q received a 12-week regimen of quetiapine, up to 150 mg/day as tolerated (n = 28). During the follow-up visits at weeks 1, 2, 4, 8, and 12, blood draws were repeated and the subjects completed the same scales that were administered upon screening.

The screening and baseline visit for HCs (n = 27) were identical to the ones for MDD subjects. After the baseline visit was completed, no further blood draws were done on HCs.

Results: When Cohort-Q and Cohort-E participants were grouped together (n = 48), MDD subjects were found to have an elevated baseline aCL IgM (19.9 ug/ml) compared to healthy controls (8.32 ug/ml) (p = 0.0062). aCL IgM was found to have a statistically significant correlation with HAMD-17 scores at baseline in MDD subjects (p = 0.0185, r = 0.296).

Looking at the individual cohorts, Cohort-Q MDD subjects had a significantly elevated baseline aCL IgM level when compared to Cohort-E MDD subjects (p = 0.0083). On the other hand, only Cohort-E MDD subjects evidenced a significant correlation at baseline between aCL IgM level and HAM-A score (p = 0.0392, r = 0.4327); they also showed a significant inverse correlation between week 12 HAMD Item #10 (Anxiety, Somatic) and week 12 aCL IgM level (p = 0.0268, r = -0.5516).

Neither the combined nor individual cohorts displayed any significant change in aCL IgM throughout the course of the medication trials, regardless of treatment response.

When comparing the change in Cohort-E MDD subjects’ aCL IgM from baseline to week 12 versus the change in Cohort-Q MDD subjects’ aCL IgM from baseline to week 12, there was no statistical difference.

The two MDD groups differ significantly in sex, with 55.32% of Cohort-Q being female versus 78.05% of Cohort-E (p = 0.0416), and age (Cohort-Q mean age = 43.79, Cohort-E mean age = 37.56, p = 0.0169).

Conclusions: MDD subjects had significantly higher serum levels of aCL IgM when compared to HCs. Moreover, at baseline, the higher the aCL IgM level, the higher the depression severity, as measured by HAMD-17 score. However, this study did not demonstrate that aCL IgM levels changed significantly throughout a 12-week course of antidepressant treatment and revealed no correlation between changes in depressive symptoms and changes in aCL IgM levels. Baseline aCL IgM could not predict treatment response. We conclude that, despite its minimal predictive ability, serum levels of aCL IgM have a diagnostic potential in MDD that necessitates further exploration. Future studies would benefit from including aCL IgM in their inflammatory biomarker panels and from extending their observational period beyond the clinical trial, as the anti-inflammatory effects of antidepressants may be seen only after depressive symptoms have been stabilized.

Additionally, we speculate that the differences in each cohort’s respective exclusion criteria led to the differences in results. Cohort-Q excluded treatment-resistant MDD subjects. Cohort-E did not. Being that co-morbid anxiety is a risk factor for treatment-resistant MDD, this could explain why Cohort-E subjects were more anxious, based on HAM-A score. As such, we recommend future studies identify which subjects have treatment-resistant MDD, first episode MDD, and other subsets of MDD prior to drawing conclusions.

Keywords: Depression Inflammation Cytokine, Cardiolipin, Antidepressant

Disclosure: Nothing to disclose.

P298. Predictors of Functional Impairment in Bipolar Disorder: Results From 13 Cohorts From Seven Countries by the Global Bipolar Cohort Collaborative

Katherine Burdick, Caitlin Millett*, Andrew Nierenberg, Melvin McInnis

Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, United States

Background: Persistent functional impairment is common in bipolar disorder (BD) and is influenced by a number of demographic, clinical, and cognitive features. The goal of this project was to estimate and compare the influence of key factors on community function in multiple cohorts of well-characterized samples of individuals with BD.

Methods: Thirteen cohorts from 7 countries included n = 5,882 individuals (both male and female) with BD across multiple sites. The approach was planned as purposefully simplistic with a focus on one question via systematic uniform application of analyses across sites. First, each site was asked to empirically identify how they defined ‘good versus poor’ functioning in their cohort. Sites were required to dichotomize whatever measure was chosen for defining function in their study, such that individuals with BD were described as having either good or poor functional status. Sites were instructed to conduct a logistic regression with the functional outcome as the dependent variable while model-level and predictor-level results were collated. The results of each site’s logistic regression were then compared descriptively side-by-side, i.e., the goal herein was to find consistencies across samples and to identify where differences exist by individual site. Thus, meta-analyses were not conducted, rather a multiple cohort replication and expansion approach was used.

Results: Akin to prior work, we found high rates of functional impairment, ranging from 41-75%. Poor community functioning was associated with depressive symptoms in 10 of 12 of the cohorts that included this variable in the analysis (all p-values < 0.05). Lower levels of education (in 3 of 12 cohorts, all p-values < 0.1), a greater number of prior manic (2 of 7 cohorts, all p-values < 0.1) or depressive (2 of 8 cohorts, all p-values < 0.05) episodes, presence of a comorbid substance use disorder (2 of 8 cohorts, all p-values < 0.1), and a greater total number of psychotropic medications (in 2 of 7 cohorts, all p-values < 0.05) were also associated with poor functioning.

Conclusions: While our results are largely confirmatory of previous within-study reports, this study provided an opportunity to survey the global landscape of current data, identify the challenges inherent to conducting global collaborative research in this area, and highlight the overt need for future collaborative work that will identify specific contributors to continued functional impairment in BD to prioritize targets of intervention. The bipolar clinical research community is poised to work together to characterize the multi-dimensional contributors to impairment and address the barriers that impede patients’ complete recovery. Likewise, we must also identify the core features which enable many to thrive and live successfully with BD. A large-scale, worldwide, prospective longitudinal study focused squarely on BD and its heterogeneous presentations will serve as a platform for discovery and promote major advances toward optimizing outcomes for every individual with this illness. We thank the National Alliance for Mental Illness (NAMI) for their generous support of this project (to KEB, AN, and MM).

Keywords: Functional Impairment, Depressive Symptoms, Mood Disorders, Heterogeneity

Disclosure: Nothing to disclose.

P299. Polygenic Risk for Depression is Associated With Altered Dentate Gyrus Structure in Offspring at Family Risk for Depression

Milenna van Dijk*, Olivia Olmo, Irina Pokhvisneva, Sachin Patel, Jiook Cha, Marc Gameroff, Jonathan Posner, Michael J. Meaney, Myrna Weissman, Patricia Silveira, Ardesheer Talati

Columbia University, New York State Psychiatric Institute, New York, New York, United States

Background: Numerous studies showed an increased (2-5 fold) risk for major depressive disorder (MDD) and other psychopathology in the offspring of a parent with depression. MDD in two previous generations (grandparents and parents) is associated with even higher rates of psychopathology in the third generation. While these clinical findings are well-replicated, efforts to explain the mechanisms underlying family risk for depression are ongoing. One area of study is the dentate gyrus (DG) subfield of the hippocampus, which both rodent and human studies suggest may be important in determining which high-risk individuals are susceptible to depression. Mice susceptible to depressive behaviors have altered DG structure (e.g. decreased neurogenesis) and increasing or decreasing the activity of DG mature granule cells can respectively induce or reverse depressive-like behaviors. We have shown that humans at high family risk for depression have decreased DG structure, which predicts future, but not current or past, depressive symptoms. However, whether genetic risk for MDD may contribute to individual differences in DG structure, or that it is due to greater likelihood of an adverse childhood environment, has not been determined. Here we present data on the role of genes, measured by a polygenic risk score (PRS) for MDD, and early life trauma in our previous findings of decreased DG structure in offspring at family risk for depression.

Methods: Sample: The overall sample includes N = 244 children, G2, and grandchildren, G3 of probands (G1) with and without MDD. G2 and G3 offspring of G1 probands with MDD were classified as high-risk for MDD; those of probands without MDD as low risk. A subset of N = 110 participants underwent MRI scanning.

Imaging: MRI scanning was performed with a GE Signa 3 Tesla whole-body scanner with an 8-channel, phased array head coil. To evaluate structural differences, Freesurfer 6.0 was used on T1-weighted structural scans for (para)hippocampal segmentation “FS60” into 12 subfields, of which we evaluated the DG regions CA4 and GCMLDG. To investigate DG microstructural differences, mean diffusivity, a measure thought to reflect neural integrity, was assessed. DG mean diffusivity was assessed using diffusion MRI with MRtrix analytic pipeline.

Genotyping was done using the Global Screening Array v.3. A total of 10079k SNPs were available for analysis after quality control and imputation procedures. Depression PRS and Schizophrenia were calculated from the Broad depression GWAS summary statistics from Howard et al. and from summary statistics from the Schizophrenia Working Group of the Psychiatric Genomics Consortium et al., using PRSoS accelerated pipeline for each participant at different GWAS p-value thresholds (p < 10-8, p < 10-6, p < 10-5, p < 10-4, p < 10-3, p < 0.01, p < 0.05, p < 0.1, p < 0.5).

Measures: Diagnoses were assessed using the Schedule for Affective Disorders and Schizophrenia (SADS) and/or SADS for school-aged children (K-SADS), as appropriate. Depressive symptoms were measured using PHQ-9 and rumination scales. Disability was assessed using the WHODAS. Early life trauma was assessed by the K-SADS traumatic events module.

Statistical Analyses: Statistical analyses were conducted in R using generalized estimating equations (GEE) to account for family structure in the data.

Results: All analyses included adjustments for sex, and ancestry. Family history of depression was associated with higher MDD, but not schizophrenia, PRS, indicating increased cumulative genetic risk for MDD (b = 0.43, p = 0.01, thresholded at p < 0.1 and up). We then found that MDD (but not schizophrenia) PRS was associated with higher depressive symptoms (b = 0.2, p = 0.02, threshold p < 0.01), with more rumination (b = 0.21, p = 0.007 at threshold p < 0.01, marginal at higher thresholds) and with higher disability scores (b = 0.2, p = 0.003, threshold p < 0.1 and up), also adjusting for a family and personal history of depression.

Next, we found that MDD PRS predicted smaller left DG volume (left: b = -0.16 p < 0.05, threshold p < 0.5), and lower right DG microstructure as measured by higher mean diffusivity (b = 0.23, p = 0.005, threshold p < 0.001 and p < 0.01), also adjusting for a lifetime history of depression, family risk for depression, total brain volume and age, suggesting a genetic effect of MDD on dentate gyrus structure.

Interestingly, while early life trauma by itself was not associated with DG structure, early life trauma interacted with MDD PRS (b = -0.33, p < 0.001, thresholds p < 0.01 and higher), showing that DG volume was only decreased in participants who experienced early life trauma (simple slope: b = -0.38, p = 0.03), while there was no association between MDD PRS and DG volume in those who had not (simple slope: b = 0.09, p = 0.62).

Conclusions: These findings suggest that genetic variation associated with depression predisposes to smaller dentate gyri, particularly in individuals who experience trauma early in life. Findings of smaller DG volumes in depression are therefore likely not just a consequence of disease, but determined by a combination of genetics and increased early adversity. A better understanding of the mechanisms of depression susceptibility can identify individuals most likely to develop depression early, and, as existing interventions can regulate the DG, can ultimately guide interventions for those at particular risk.

Keywords: Hippocampus, Depression, Polygenic Risk Scores

Disclosure: Nothing to disclose.

P300. Translational Profile of Genes in Prefrontal Parvalbumin Interneurons Following Chronic Stress

Nawshaba Nawreen*, Naim Mahi, Marissa Smail, Bob Thompson, James Herman

University of Cincinnati College of Medicine, Cincinnati, Ohio, United States

Background: Hypofunction of the prefrontal cortex (PFC) contributes to stress-related neuropsychiatric illnesses. Previous finding from our lab indicates chronic stress enhances spontaneous miniature inhibitory neurotransmission in the PFC. Although it is clear that GABAergic transmission in the PFC undergoes significant alterations during chronic stress, little is known about the mechanisms leading to prefrontal hypoactivity. Mounting evidence suggests that chronic stress leads to an increase in activity of parvalbumin (PV) expressing GABAergic interneurons (INs) in the PFC. As a result, the goal of this study was to elucidate the gene expression profile of parvalbumin interneurons in the prefrontal cortex following exposure to chronic stress.

Methods: Transgenic mice Rosa26L10a-eGFP/L10a-eGFP; PVcre/+ were generated that expressed an EGFPL10a ribosomal fusion protein under control of the PV promoter. Male mice were subjected to the chronic variable stress (CVS) paradigm which comprised of a series of randomly alternating stressors administered twice daily over a period of 14 days or served as non-stressed controls. 24 hours after cessation of the stress protocol, we isolated translating ribosomes specifically from prefrontal parvalbumin interneurons using the Translating Ribosome Affinity Purification (TRAP) technique followed by RNA-seq analysis. Data were analyzed using targeted pathway analysis using Enrichr and full transcriptome analysis using GSEA. Potential drug interactions across the top 1000 gene signatures (‘perturbagens’) were analyzed using ILINCs.

Results: Over 442 genes were ≥1-fold enriched in parvalbumin interneurons following chronic stress compared with the control no stress condition, including targets with known relevance to oxidative stress, extracellular matrix, phospho-lipid metabolism and neurotransmitter binding and activity. At pathway level, we have found changes in oxidative phosphorylation (mitochondrial electron transport), neurotransmission and changes in lipid metabolism and transport. Our drug-target analysis supports the involvement of neurotransmission and growth factor related changes following chronic stress. The analysis of leading-edge genes revealed differentially regulated set of genes relevant to cell binding/growth and mitochondrial function (encoding respiratory chain complex and electron transport chain proteins) following chronic stress in prefrontal PV INs.

Conclusions: Collectively, these results provide new insight into the potential molecular mechanisms and druggable targets associated with chronic stress induced changes in prefrontal GABA-ergic parvalbumin interneurons and how that may lead to stress-related illnesses. Further experiments are needed to validate these findings in stressed vs controls animals and to determine whether alterations in specific target genes in PV INs may lead to stress related phenotypes.

Keywords: Gaba Neuron, Parvalbumin Neurons, Chronic Stress, Medial Prefrontal Cortex, RNA Sequencing

Disclosure: Nothing to disclose.

P301. Expression of the Astrocyte-Specific Extracellular Matrix Gene Htra1 Regulates Susceptibility to Stress in a Sex-Specific Manner

Eric Parise*, Trevonn Gyles, Omar Sial, Arthur Godino, Caleb Browne, Lyonna Parise, Angelica Torres-Berrio, Marine Salery, Romain Durand-de Cuttoli, Leanne Holt, Yentl Van der Zee, Zachary Lorsch, Flurin Cathomas, Juliet Garon, Collin Teague, Orna Issler, Peter Hamilton, Carlos Bolanos-Guzman, Scott Russo, Eric Nestler

Icahn School of Medicine at Mount Sinai, New York, New York, United States

Background: While the underlying pathophysiology of major depressive disorder (MDD) is poorly understood, convergent evidence from pre-clinical and clinical research supports the notion that MDD is related to impaired structural plasticity in key limbic regions. The extracellular matrix (ECM) of the brain represents a novel domain for study as it not only provides structural support, but also is intimately involved in regulating synaptic plasticity and remodeling.

Methods: We analyzed transcriptional profiles of ECM-related genes from the nucleus accumbens (NAc) in postmortem brain tissue of both male and female patients with MDD as well as in mice exhibiting depression-like behavioral abnormalities after exposure to 21 days of chronic variable stress (CVS). After identifying ECM-related genes that were similarly dysregulated across species, we confirmed cell-type-specificity using in situ hybridization in male and female mice exposed to CVS. Next, to determine causal links, we utilized viral vectors designed to overexpress or knockdown the expression of target genes in a cell-type specific manner and assessed behavioral reactivity to sub-threshold exposure to stress. In a separate cohort of mice, we assessed for changes in the electrophysiological properties of DA neurons recorded in vitro in mice following cell-type specific manipulation of target genes combined with sub-threshold exposure to stress.

Results: We identified Htra1, an astrocyte-enriched secreted serine protease, as being significantly down-regulated in the NAc of males and up-regulated in females across both species. We found that selective manipulation of the Htra1 gene in astrocytes within the mouse NAc bidirectionally controls susceptibility to stress in a sex-specific manner. Furthermore, direct manipulation of Htra1 in astrocytes of the NAc, in conjunction with sub-threshold stress, influences medium spiny neuronal signaling.

Conclusions: Our findings reveal a pivotal role of astroglia as well as the brain’s ECM in mediating stress vulnerability that is impacted in a sex-specific manner and set the stage for novel therapeutic approaches for MDD.

Keywords: Chronic Stress, Major Depressive Disorder (Mdd), Extracellular Matrix, Astrocyte, Sex Differences

Disclosure: Nothing to disclose.

P302. Exploring Genetic Variation of Cytochrome C Oxidase Subunit IV as Potential Marker of Increased Mitochondrial Function Associated With Antidepressant-Induced Mania

Manuel Gardea Resendez*, Brandon J Coombs, Marin Veldic, Susannah Tye, Francisco Romo Nava, Nicolas Nunez, Alfredo Cuellar-Barboza, Balwinder Singh, Miguel Prieto, Aysegul Ozerdem, Joanna Biernacka, Susan McElroy, Tamas Kozicz, Mark Frye

Mayo Clinic, Rochester, Minnesota, United States

Background: Mechanistically, the Wnt signaling pathway has been postulated to mediate antidepressant response; similarly, individual’s bioenergetic status may also impact treatment response. In vitro and in vivo studies have also shown that antidepressants can influence electron transport chain (ETC) complex activity, either by increasing (Mito+) or decreasing (Mito-) mitochondrial energetics. A preclinical antidepressant-induced mania-like phenotype has been associated with an increased respiratory control ratio (State 3/State 4), catalyzed by cytochrome C oxidase (COX). COX is involved in the final step of the ETC to generate ATP and is encoded by ten nuclear and three mitochondrial (mt) DNA. We hypothesize that the rate of antidepressant induced mania (AIM+), a standardized biobank clinical phenotype, will be higher in antidepressants that increase mitochondrial energetics (Mito+), in comparison to Mito- antidepressants. We additionally sought to investigate whether genetic variants in nuclear genes that encode for the COX enzyme are associated with AIM + .

Methods: Based on existing literature, we classified antidepressants as Mito + (venlafaxine, paroxetine, nortriptyline, bupropion) or Mito- (escitalopram, amitriptyline) and identified genotyped patients from the Mayo Clinic Bipolar Biobank, with history of use of Mito+ or Mito- antidepressants. Patients were then categorized and analyzed based on retrospective assessment of AIM and by antidepressant Mito status (+ or -). In a subset analysis, using logistic regression adjusting for the first principal component of ancestry, we tested whether genetic variations in 10 nuclear genes (1895 SNPs in total) encoding for COX (COX10, CO14, COX15, COX20, COX4I2, COX6A1, COX6B1, COX7B, Fastkd2, PET100) was associated with AIM + with antidepressant Mito+ activity. To reduce multiple testing, we combined the SNP-level results into gene-level tests of association using MAGMA for generalized gene analysis of GWAS data. Additionally, GWAS results were combined with eQTL data for cross-tissue expression using FUSION to assess whether genetically predicted gene expression of the candidate genes is associated with AIM + .

Results: Bipolar participants with AIM + (n = 129) and AIM- (n = 597) phenotypes were further classified into Mito + (n = 481) and Mito- (n = 245). While accounting for patient overlap in the two groups, AIM + was more frequent with Mito+ vs. Mito- antidepressant use (21.1% vs. 10.6%; OR = 2.1; p < 0.001). Gene-level results showed no significant association between genes that encode the COX enzyme and AIM + in response to use of antidepressants with Mito+ activity. Further, eight COX genes, estimated in the cross-tissue eQTL FUSION analysis (COX20, COX6B1, COX6A1, COX14, PET100, COX10, COX15, Fastkd2) showed no significant gene-trait association with AIM when combined with the gene-level results.

Conclusions: These data suggest categorizing antidepressants based on mitochondrial energetics, and not conventional mechanism of action (SSRI, TCA, etc), may be of value in future larger clinical and pharmacogenomic studies of antidepressant-induced mania. Despite evidence showing a possible link between mitochondrial function and bipolar disorder, these data did not provide evidence to support the hypothesis of mitochondrial abnormalities, as defined by variations in COX-related nuclear genes, in AIM + participants with antidepressants that positively impact mitochondrial bioenergetics. No genome-wide significant loci in any of the GWAS was identified but were underpowered for detecting hypothetical effect size. Future assessments focusing on different ETC complexes and analysis of mtDNA genes may provide more insights into the relationship between AIM + and mitochondrial energetics.

Keywords: Bipolar Disorder, Mitochondrial Respiration, Antidepressant Induced Mania, Genetic Variation

Disclosure: Nothing to disclose.

P303. In Vitro Modeling of Depression Neurobiology: Differentiating Blood-Derived Neural Progenitor Cells into Hippocampal-Like Neurons

Anastasiya Nestsiarovich*, Thomas Kuret, Alannah Miranda, John Kelsoe

University of California San Diego, San Diego, California, United States

Background: In vitro modeling of mood disorders deploying recent advances in stem cell reprogramming offers a unique alternative to postmortem brain studies. Few laboratories to date have examined induced pluripotent stem cells (iPSC)- derived neurons from patients with mood disorders, in part due to the complexity of the method. Our UCSD laboratory has worked closely with collaborators at the Salk Institute who have developed protocols for differentiation of iPSCs to different neuronal types. In particular, we have studied the response of stem cell-derived hippocampal granule cells from patients with bipolar disorder to lithium in vitro. In this study, we aimed to reproduce this protocol and generate dentate gyrus hippocampal-like neurons from neural progenitor cells (NPCs) derived from patients with major depressive disorder for further in vitro experimentation modeling pharmacological response.

Methods: NPCs available from a UCSD-stored cellular bank were transfected with a Prox1:GFP lentiviral vector, plated on Poly-L-Ornithine/Laminin coated 6-well plates, and cultured for 22 days in differentiation and maturation medium. Cytosine arabinose was added to the half of cell colonies prior to FACsorting to help select well-differentiated dentate gyrus (DG)-like neurons.

Results: We have received well-differentiated colonies of DG hippocampal-like neurons which were able to generate electrical signals on the microelectrode plate. Adding cytosine arabinose improved the output of the FACsorting procedure.

Conclusions: Successful reproduction of the suggested differentiation protocol validates the use of UCSD-stored NPC bank for further in vitro experimentation to answer clinical questions.

Keywords: Stem Cells, Neuron, Major Depressive Disorder, Neural Progenitor Cells, In Vitro Neuronal Differentiation

Disclosure: Nothing to disclose.

P304. Amygdala, Orbitofrontal, and Medial Prefrontal Activation During Implicit Facial Emotion Processing Distinguish Young Adults With Low and High Levels of Negative Urgency From Those With Bipolar Disorder

Maya C. Schumer*, Michele A. Bertocci, João Paulo Lima Santos, Lisa Bonar, Mary Kay Gill, Halimah Abdul-Waalee, Genna Bebko, Richelle Stiffler, Jeanette C. Lockovich, Haris A. Aslam, Boris Birmaher, Amelia Versace, Henry W. Chase, Simona Graur, Sheri L. Johnson, Mary L. Phillips

University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Background: Bipolar disorder (BD) is a debilitating condition manifested during late adolescence through early adulthood and marked by difficulty regulating emotions and emotion-triggered impulsivity, which is prevalent during hypo/manic and mixed episodes and persists during inter-episode periods. Alterations to medial-lateral prefrontal cortical and subcortical emotion-processing and emotion-regulation neural circuitry have been shown to characterize BD. Neuroimaging may additionally identify objective markers of BD risk in this circuitry. The negative affective components of hypo/mania and mixed states are characterized by negative urgency (NU), the tendency to impulsively respond to negative affect. High NU is evident in adults with BD, and one study to date has shown that NU statistically mediates the relationship between reward-related neural circuitry and measures indicative of hypo/mania in transdiagnostic individuals at-risk for BD. The relationship between NU and emotion-processing neural circuitry has not been examined in these individuals. The present study compares transdiagnostic young adults (n = 224) to individuals diagnosed with BD (n = 59) during a functional magnetic resonance imaging (fMRI) task assessing implicit emotion processing to determine the extent to which emotion-processing neural circuitry can distinguish individuals with differing risk levels for BD, based on NU.

Methods: 283 young adults (22.34 ± 2.92 years, 65.37% female) were scanned by 3T fMRI while viewing angry, fearful, sad, and happy faces. The Urgency, Premeditation (lack of), Perseverance (lack of), Sensation Seeking, Positive Urgency (UPPS-P) Impulsive Behavior Scale assessed NU in the transdiagnostic sample, which was median-split into low NU (n = 113) and high NU (n = 111) groups. Two different scanners were used during data collection, thus, fMRI data were harmonized using ComBat, a statistical harmonization method that mitigates measurement differences attributable to scanner effects while preserving inter-subject variability. Emotional face-related activity was examined using two region-of-interest (ROI) approaches: anatomical and meta-analytic. The anatomical ROIs consisted of a priori regions known to be involved in emotion-processing in BD, such as the caudate, putamen, ventral striatum (VS), amygdala, orbitofrontal cortex (OFC), medial and ventrolateral prefrontal cortices (MPFC, VLPFC), and the ventral and dorsal anterior cingulate. Meta-analytic ROIs were selected from a recent meta-analysis of cognitive, emotional, and resting-state BD functional neuroimaging studies conducted by our lab that identified the anterior caudate, VS, posterior cingulate, ventral anterior cingulate, amygdala, superior temporal gyrus, OFC, and VLPFC. Parameter estimates for regions within each ROI for each emotional face were separately extracted. Separate regularized regression analyses were completed for the anatomical and meta-analytic ROIs to assess group differences in a multinomial logistic framework with age and sex covariates included in the model given significant differences (p < 0.001 and p = 0.01, respectively).

Results: Elastic net regression cross-validation identified 5 neuroimaging and 1 demographic (age) non-zero predictor variables that optimized model fit. A Nagelkerke pseudo r-squared indicated that 19.1% of the variance in group was explained by these predictors, and the final model was significant at p < 0.001. The 5 neural activity variables were: 2 variables to angry faces (right amygdala and left lateral OFC), 1 variable to fearful faces (right lateral OFC), one variable to sad faces (left MPFC), and 1 variable to happy faces (right medial OFC). Post-hoc Tukey HSD-corrected tests individually comparing low NU and high NU to BD indicated that low NU and high NU had significantly lower amygdala activity to anger versus BD (p < 0.001 and p = 0.004, respectively); low NU and high NU had significantly lower left lateral OFC activity to anger versus BD (p < 0.001 and p = 0.004, respectively); high NU had significantly lower left MPFC activity to sadness versus BD (p = 0.019); and low NU and high NU had significantly greater right medial OFC activity to happiness versus BD (p = 0.003 and p = 0.004, respectively). The elastic net model with meta-analytic ROIs did not yield any non-zero predictor neuroimaging variables.

Conclusions: These findings provide preliminary evidence suggesting that emotion-processing alterations in limbic and prefrontal circuity in individuals with both low and high trait NU may be emotion-triggered impulsivity-based objective vulnerability markers for BD that are prominent during young adulthood.

Keywords: Bipolar Disorder, fMRI Biomarkers, Negative Urgency, Facial Emotion Processing, Impulsivity

Disclosure: Nothing to disclose.

P305. Comparison of Interleukin-8 Levels in Major Depressive Disorder and Bipolar Depression After Treatment With Escitalopram

Adriana Cantos*, Monica Feliz Castillo, Angelos Halaris

Loyola University Chicago Stritch School of Medicine, Forest Park, Illinois, United States

Background: Depressive symptomatology in Major Depressive Disorder (MDD) and Bipolar Disorder (BD) can have severely negative effects on patients’ quality of life and can lead to very harmful consequences. Although much progress has been made in the understanding and treatment of affective disorders, a significant number of patients are nonresponsive or partially responsive to current treatment modalities. Neuroinflammation and cytokine dysregulation appear to be key contributors to the pathophysiology of affective disorders, including MDD and BD. Interleukin-8 (IL-8) is a pro-inflammatory chemokine that is activated during periods of acute inflammation. Growing evidence supports IL-8 dysregulation in MDD and BD. We present findings on IL-8 from two studies of patients with MDD and treatment resistant bipolar disorder depression (TRBDD) who were treated with escitalopram (ESC), a selective serotonin reuptake inhibitor. While we assessed a panel of various inflammatory biomarkers for these studies, in this poster we discuss our analysis of IL-8. We present data on only those subjects who received ESC treatment either alone or in combination with an anti-inflammatory agent.

Methods: Data from two separate studies were used for this analysis. In the first study, participants (n = 66) ages 20-65, who had been diagnosed with MDD by DSM-IV criteria were included in the study. Study participants with MDD were treated with either escitalopram (ESC) or quetiapine (QTP) for a total of 12 weeks. Serum inflammatory biomarkers were measured at baseline and week 12. The Hamilton Depression Scale (HAM-D) 7, 17, and 21were administered at those two time points. Additionally, baseline serum IL-8 levels of 24 participants without a significant past medical history were also included in this study as healthy controls (HC). Paired sample t-tests were conducted to analyze IL-8 levels for those treated with ESC in this study. Pearson correlation coefficients were calculated to analyze the relationship between IL-8 and depressive symptomatology at week 12 for study completers. In the second study, participants (n = 47) who had been diagnosed with TRBDD (Bipolar Disorder I or II) were included in this randomized, double-blind trial. Participants were randomized to receive ESC + placebo or the combination of ESC + celecoxib (CBX) for an 8-week treatment period. HAM-D scores and serum inflammatory biomarker levels were determined at baseline and week 8. HC subjects (n = 30) also had baseline serum IL-8 levels assessed. Paired sample t-tests, Kruskal Wallace test, and linear effects models were conducted.

Results: For the MDD study, baseline IL-8 values were significantly different between MDD (Mean ± SEM) (4.02 ± 0.71) and HC (1.86 ± 0.34) participants (p = 0.007). In study completers, there was no statistically significant correlation between IL-8 levels and HAM-D scores at week 12 of treatment. Furthermore, for study completers who received ESC (n = 17), there was no statistically significant difference in serum IL-8 values between baseline (6.10 ± 2.14) and week 12 (4.85 ± 1.36) of treatment (p = 0.653). In the BDD study, baseline serum IL-8 levels were significantly different between the BDD participants (3.92 ± 0.53) and the HC subjects (2.21 ± 0.47) (p = 0.0021). There was no statistically significant difference between serum IL-8 levels or HAM-D scores over the 8-week treatment period. In those who received ESC, there was no statistically significant difference between baseline (4.15 ± 0.85) and week 8 values (3.77 ± 0.70) (p = 0.394). Likewise, in those who received ESC + CBX, there was no statistically significant difference between baseline IL-8 values (3.73 ± 0.73) and week 8 IL-8 values (3.09 ± 0.29) (p = 0.363).

Conclusions: Baseline serum IL-8 values were significantly elevated in both the MDD and BDD participants compared to the HC participants. This supports the inflammatory dysregulation hypothesis in patients with depressive mood disorders. Overall, there was no statistically significant correlation between IL-8 levels and depressive symptomatology in patients with MDD or BDD after being treated with escitalopram. Baseline IL-8 levels did not predict treatment response. This suggests that IL-8 may not play a critical role in the antidepressant effect of escitalopram.

Keywords: Neuroinflammation, Interleukin-8, Major Depressive Disorder, Bipolar Depression, Escitalopram

Disclosure: Nothing to disclose.

P306. Longitudinal Increase in CSF sTREM2 is Associated With Increased Markers of CSF AD Pathology in Late-Life Major Depression Potentially Reflecting a Compensatory Mechanism

Nunzio Pomara*, Chelsea Reichert Plaska, Jaime Ramos-Cejudo, Davide Bruno, Ricardo Osorio, Amanda Heslegrave, Anilkumar Pillai, Henrik Zetterberg, Kaj Blennow

Nathan S Kline Institute/New York University School of Medicine, Orangeburg, New York, United States

Background: Triggering receptor expressed on myeloid cells 2 (TREM2) is a transmembrane innate immune receptor of the immunoglobulin family. In the brain, TREM2 is found exclusively on microglia and its stimulation has been associated with anti-inflammatory and protective effects. Activation of TREM2 also results in the formation of a proteolytic soluble product (sTREM2). Higher baseline CSF sTREM2 concentrations have been associated with a slower rate of cognitive decline and decreased longitudinal brain amyloid deposition in Alzheimer’s disease (AD). Thus, it has been proposed that CSF sTREM2 might reflect an anti-inflammatory state. In a previous study by our group (ACNP presentation 2017), cognitively unimpaired individuals with late-life major depression (LLMD) which is associated with increased risk for AD, showed significant reductions in CSF sTREM2 levels and a lack of significant correlations with CSF AD biomarkers compared to controls, consistent with the aforementioned hypothesis and that TREM2- mediated anti-inflammatory microglia activation might be impaired in this disorder. In the current report, we examined the relationship between longitudinal changes in CSF sTREM2 during a 3-year period and their relationship to LLMD diagnosis and changes in AD and inflammatory markers.

Methods: Our baseline sample consisted of 51 subjects aged 60 years and older who completed a longitudinal observational study over three years and an optional lumbar puncture (LP). 38 of these individuals completed the LP at year 3 (20 with LLMD and 18 controls). We evaluated the effects of time on CSF TREM2 with related-samples Wilcoxon Signed Rank Test and the effect diagnosis on change in CSF sTREM2 with Mann Whitney U test. Correlations between change in CSF sTREM2 and CSF markers of AD (Aβ42, Aβ40, total-tau, p-tau181), inflammation (Il-6, Il-8), and Complement component 3 (C3) markers were run with Spearman’s Rank test.

Results: Baseline CSF sTREM2 was significantly lower in the LLMD group vs controls (p = 0.03). There were no group differences in CSF sTREM2 from baseline to Year 3 (LLMD p = 0.82, Controls p = 0.18), nor did Year 3 differ between the LLMD and control group (p = 0.35). No differences were observed between controls and LLMD for the longitudinal change in CSF sTREM2, AD biomarkers and inflammatory markers. In the whole group, change in sTREM2 was significantly moderately correlated with change in CSF Aβ40 (rho = 0.54, p < 0.001), Aβ42 (rho = 0.48, p = 0.003), and PTau181 (rho = 0.34, p = 0.04).

In the control group, change in sTREM2 was significantly correlated with change in CSF Aβ40 (rho = 0.58, p = 0.01) and Aβ42 (rho = 0.56, p = 0.02).

In the LLMD group, change in sTREM2 was significantly correlated with change in CSF Aβ40 (rho = 0.50, p = 0.03), Tau (rho = 0.44, p = 0.05) and P-Tau181 (rho = 0.52, p = 0.02) but not with change in CSF Aβ42, a more specific marker of cerebral amyloidosis.

Change in inflammatory markers (i.e., IL-6, IL-8) were not significantly correlated with change in sTREM2 (p > 0.05) for LLMD or controls, or the whole group. Change in sTREM2 was significantly correlated with C3 (rho = 0.35, p = 0.04) in the whole group.

Conclusions: There were no group differences in change in CSF sTREM2 during a 3-year period, nor any difference between baseline and year 3. The longitudinal increase in CSF sTREM2 during a 3-year period and its association with CSF AD biomarkers may reflect increased anti-inflammatory microglia activation and phagocytosis in response to pathological forms of AD biomarkers Aβ, tau, and p-tau 181.

Interestingly, the CSF sTREM2 increase was associated with the increase CSF Aβ42 in controls, but not in LLMD. This finding suggests that upregulation of anti-inflammatory microglia and phagocytosis of brain amyloid deposits may be less efficient in LLMD.

Similarly, the positive correlation between the longitudinal increase in CSF sTREM2 and the increase in CSF T-tau and P-tau181, which we found in the LLMD group but not in controls is also consistent with an upregulation of anti-inflammatory microglia in response to increased tau and neurofibrillary tangles, markers of neurodegeneration and AD, respectively.

However, the change in CSF sTREM2 was correlated with the change in CSF C3 in the whole cohort; our group and others have also found positive correlations between CSF sTREM2 and CSF neurofilament light (NFL) protein, a biomarker of neuroaxonal damage.

Taken together these results suggest that higher CSF sTREM2 concentrations may reflect not only upregulation of anti-inflammatory microglia and phagocytosis in response to increased brain amyloid and tau pathology, but also increased neurotoxic effects which are possibly related to its reported intrinsic pro-inflammatory effects.

Keywords: CSF sTREM2, Microglia, Aβ, Depression, Alzheimer’s Disease

Disclosure: Nothing to disclose.

P307. High Psychiatric Comorbidity Denotes a Candidate Bipolar Disorder Sub-Phenotype Marked by Low Prefrontal GABA Levels and High Impulsivity: A Preliminary 2x2 (Anxiety Disorder X Alcohol Use Disorder) Factorial MRI Investigation

James Prisciandaro*, William Mellick, Helena Brenner, Bryan Tolliver, Raymond Anton

Medical University of South Carolina, Charleston, South Carolina, United States

Background: Though nearly 80% of individuals with bipolar disorder (BD) experience anxiety (ANX) and/or substance use (SUD) disorders at some point in their lives, relatively few studies have focused on the impact of co-occurring ANX and/or SUD on BD pathophysiology or treatment. Over the past decade, we have focused on characterizing and manipulating disturbances in glutamatergic (excitatory) and GABAergic (inhibitory) neurotransmission and neurobehavioral control that are shared between individuals with BD and Alcohol Use Disorder (AUD). We have found that individuals with co-occurring BD + AUD have uniquely-low dorsal anterior cingulate cortex (dACC) GABA and glutamate levels, uniquely-low activation to alcohol cues in the right inferior frontal gyrus (rIFG; i.e., the main locus of inhibitory control in the brain), and the highest levels of impulsive choice (i.e., delay discounting) relative to healthy-volunteer, BD or AUD alone comparator groups. However, despite emerging evidence that ANX are independently associated with dysfunctional GABAergic/glutamatergic transmission and impulsivity, we have failed to date to account for the potential moderating impact of ANX on our findings. To address this oversight, we re-analyzed our published GABA, glutamate (1H-MRS; Prisciandaro, 2017), alcohol cue reactivity (fMRI; Prisciandaro, 2019), and delay discounting (behavioral task; Mellick, 2019) data, with ANX moderating the effects of AUD on these variables in individuals with BD (+/-AUD; n = 56) from the lead author’s K23 study (AA020842).

Methods: All K23 study participants were required to demonstrate ≥1 week of abstinence from alcohol and drugs via serial ethyl glucuronide and urine drug screen testing. General exclusions included serious medical illness, history of head injury, severe co-occurring Axis I disorders, benzodiazepine/antidipsotropic use, or history of complicated alcohol withdrawal. Co-occurring drug use disorder was exclusionary for BD but not BD + AUD participants. Participants with substantial medication dose changes ≤1 week before MRI were excluded. Participants completed a baseline diagnostic visit including the Structured Clinical Interview for DSM-IV Axis I Disorders and a delay discounting computer task. Participants then returned approximately 4 days later for an MRI including 1D/2D J-resolved 1H-MRS of dACC and a well-established fMRI visual alcohol cue exposure paradigm (MRI methods detailed in primary publications). For the present re-analysis, we divided the BD +/-AUD subsample by current diagnosis of ≥1 ANX (i.e., Panic Disorder, Agoraphobia, Social Anxiety Disorder, or Generalized Anxiety Disorder), resulting in 4 participant groups nested within a 2x2 (AUDxANX) factorial design matrix (BD [n = 17], BD + ANX [n = 14], BD + AUD [n = 13], BD + ANX + AUD [n = 12]). For each dependent variable, a 2x2 general linear model was estimated. Significant main effects and/or interactions were followed by pairwise comparisons.

Results: There were significant interactions between AUD and ANX in BD participants on levels of GABA (F = 4.38, p < 0.04), alcohol cue reactivity (i.e., in a cluster encompassing the rIFG; F > 4.03, p < 0.05 FWE), and delay discounting (i.e., LogK; F = 5.05, p = 0.03). Post-hoc mean testing found that BD participants with both co-occurring ANX and AUD had uniquely-low, while BD participants with co-occurring ANX but not AUD had uniquely-high, levels of GABA and rIFG activation to alcohol versus neutral beverage images. Delay discounting was only elevated in BD participants with both co-occurring ANX and AUD, with remaining groups statistically indistinguishable from one another. Preliminary glutamate data suggested a main effect of AUD, though analyses of complex relationships among the diagnostic groups are ongoing.

Conclusions: Results demonstrated that co-occurring ANX moderated previously reported effects of co-occurring AUD on neuro-chemical/behavioral variables in individuals with BD. In most cases, abnormalities previously attributed to co-occurring AUD in BD individuals were either specific to, or substantially more severe in, BD individuals with both co-occurring ANX and AUD. We hope to replicate and extend these findings in a larger sample with the goals of providing a neuroscience foundation for the development and evaluation of personalized treatments for “real-world” individuals with BD and alternative psychiatric classification systems that overcome the limitations inherent to the existing DSM system.

Keywords: Bipolar Disorder, Psychiatric Comorbidity, Impulsivity, Proton Magnetic Resonance Spectroscopy, Functional MRI (fMRI)

Disclosure: Nothing to disclose.

P308. Pharmacological Targeting of FGF14 Modulates Motivated Behavior by Increasing Medium Spiny Neuron Firing

Nolan M. Dvorak, Paul A. Wadsworth, Douglas S. Engelke, Aditya K. Singh, Nghi Nguyen, Giuseppe Aceto, Cynthia M. Tapia, Pingyuan Wang, Ann Wadsworth, Oluwarotimi Folorunso, Haiying Chen, Reid T. Powell, Clifford Stephan, Marcello D’Ascenzo, Fabricio H.M. Do Monte, Jia Zhou, Fernanda Laezza*

University of Texas Medical Branch, Galveston, Texas, United States

Background: Serving as the central hub of the mesocorticolimbic (MCL) circuit, the nucleus accumbens (NAc) confers prominent regulatory effects on motivated behaviors. In the principal cell type of the NAc, namely medium spiny neurons (MSN), protein:protein interactions (PPI) between voltage-gated Na + (Nav) channels and Nav channel auxiliary proteins play a central role in generating their electrical outputs. In particular, the PPI between the Nav1.6 channel and fibroblast growth factor 14 (FGF14) is central to action potential (AP) discharge of MSNs and, when the PPI is altered, there are resultant neuromodulatory effects. Given this prominent role of FGF14:Nav1.6 complex assembly in generating electrical outputs of MSNs, the central role of the NAc in regulating the MCL circuit, and the latter conferring important regulatory effects on motivated behaviors, we hypothesize that pharmacological targeting of the FGF14:Nav1.6 complex could exert regulatory effects on motivated behaviors.

Methods: We employed medicinal chemistry to synthesize and optimize, as well as chemoinformatics, the split-luciferase assay (LCA), surface plasmon resonance (SPR), and whole-cell patch-clamp electrophysiology to validate, pharmacological probes in silico to ex vivo. Compounds displaying promising in silico to ex vivo pharmacodynamic profiles were investigated in vivo using single-unit electrophysiological recordings and for effects on motivation in an operant behavior paradigm.

Results: Starting with a candidate pool of ~45,000 commercially available compounds, we employed an amalgam of complementary and orthogonal primary in-cell screening assays, in-cell counter-screening assays, and protein:ligand binding studies to identify small molecule modulators of FGF14:Nav1.6 complex assembly. Using this integrated screening platform, we identified a class of three compounds with conserved pharmacodynamic profiles suggestive of potent and selective modulatory effects on the FGF14:Nav1.6 complex. Of these 3 compounds, 7605 displayed the most favorable drug-like properties for CNS drug development, including a molecular weight less than 400 g/mol and a topological surface area less than 75 Å2. To improve the potency and aqueous solubility of 7605, substituents of the parental scaffold were replaced, producing the optimized analog PW1028. Notably, PW1028 modulated FGF14:Nav1.6 complex with an IC50 of ~250 nM according to the LCA and displayed nanomolar binding affinity to FGF14 as determined by SPR. In heterologous cells, PW1028 was shown to exacerbate FGF14-mediated regulatory effects on Nav1.6 channel inactivation. In MSNs of the NAc, these FGF14-dependent modulatory effects of PW1028 on Nav1.6 channel inactivation were recapitulated, as voltage-clamp recordings revealed that PW1028 caused a ~15 mV depolarizing shift in the voltage-dependence of steady-state inactivation of the transient Na+ current (INa) of MSNs from wild-type mice without affecting MSNs from Fgf14-/- mice. As anticipated, this hampering of Nav channel closure and prolonged INa conferred by PW1028 was shown to potentiate the intrinsic excitability of MSNs of NAc as determined using whole-cell current-clamp electrophysiological recordings. The findings of these ex vivo studies were recapitulated in vivo using single-unit electrophysiological recordings, as IP injection of 5 mg/kg PW1028 increased the firing rates of accumbal neurons. At the behavioral level, these electrophysiological changes were found to be accompanied by systemic administration of PW1028 maintaining motivational states in a satiated state, and, therefore, suggesting that the compound affects hedonic states in situations lacking motivation.

Conclusions: These results demonstrate that the FGF14:Nav1.6 complex is a novel target for the development of first-in-class PPI-targeting neuropsychopharmacological agents.

Supported by: NIH Grant R01MH095995 (FL), R01MH12435101 (FL) NIH Grant 1R01MH111107 (FL, JZ), John Sealy Memorial Endowment Funds (FL), R01 DA038446 (JZ), P30 DA028821 (JZ), CPRIT RP150578 (CS), PhRMA Foundation (PAW), NIH/NIEHS-T32ES007254 (CMT), and HAMBP training grant no. T32GM008280 (NMD).

Keywords: Neuropharmacology, Ion Channels, Reward, Neural Circuits

Disclosure: IonTx Inc.: Founder (Self)

P309. Social Dominance Hierarchies Negotiate the Response to Psychosocial Stress in an Adult Female Mouse Model of Depression

Lydia Smith-Osborne, Anh Duong, Alexis Resendez, Jonathan Fadok*

Tulane University, New Orleans, Louisiana, United States

Background: Depression is one of the most common psychiatric conditions of modernity, and it disproportionately affects women. Recently, there has been a generational trend of increased prevalence in adults. It has been postulated that this is due to the demands of competitive work environments, socioeconomic stress and relative social isolation. Why some people thrive in such environments and others develop depression is poorly understood. Rodent models of social hierarchies can be studied to investigate the psychosocial stressors and neurobiology contributing to the depressive milieu.

We hypothesize that the protective effects of social partnerships contribute to stress susceptibility in a rank-based manner. We perform our investigation in two aims – first to determine the role of rank in reward salience, and second to investigate differences in vulnerability to depression induced by social instability stress (SIS).

Methods: To investigate whether novel social contact is inherently rewarding, we pair-housed adult female C57/Bl6J mice (n = 28). Mice underwent open field test (OFT) to identify differences in anxiety, exploration, or locomotion. Social rank was assigned via competitive exclusion (CE) and home cage behavioral analysis. After hierarchies stabilized, mice underwent the three-chamber social approach (3-CSA) to gauge sociability and interest in social novelty. To investigate rank differences in biological markers of stress, fecal samples were processed for corticosterone metabolites (FCM) via ELISA. Finally, immunohistochemistry (IHC) was performed on whole brains to examine c-Fos expression after exposure to a novel conspecific (n = 12) or an empty cage (n = 8).

Remaining mice (n = 8) underwent an experiment investigating motivation and anxio-depressive responses to social isolation (SI) stress. Dyads were re-tested for rank, then subjected to OFT and elevated plus maze (EPM). They underwent appetitive conditioning (AC) to identify rank differences in reward learning. After, mice underwent 8 weeks of SI, followed by repeat OFT and EPM. The development of a depressive phenotype was monitored through weekly coat state score (CSS), nest building test (NBT), and FCM. In the 7th week sucrose preference test (SPT) was performed. After SI, mice were re-introduced to their original social partner (n = 4) or to an identical empty environment (n = 4). IHC was performed on brains for c-Fos, co-labeled for GAD67 or ChAT.

Results: Dyads rapidly formed stable hierarchies (>85% within 3 days), and rank was independent of innate anxiety or locomotor characteristics. However, subordinates expressed more supported rears during the OFT. Subordinates also spent more time exploring novel contexts in 3CSA, regardless of whether the stimulus was social or inanimate. In contrast, dominants prioritized time in social chambers.

Subordinates also demonstrated higher FCM at baseline and during hierarchy formation. As hierarchies stabilized, FCM became comparable between ranks. IHC revealed differential c-Fos expression in brain regions involved in social recognition, reward salience, and threat evaluation, including the medial prefrontal cortex, lateral septum, claustrum, nucleus accumbens, and basolateral amygdala. Cell counting is ongoing to determine if a rank-based difference exists.

Ranks learned comparably in AC training and displayed equivalent motivation to perform the task. Subordinate CSS deteriorated during SI and exploratory behavior diminished in the OFT. Dominants consumed less sucrose in the SPT ( < 60% preference) compared to subordinates. These differences were not attributable to rank differences in locomotion or anxiety in OFT and EPM. All mice experienced a progressive increase in FCM during SI. More mice (n = 20) will be tested to determine the significance of these trends.

Conclusions: Here we show that adult female dyads form stable hierarchies rapidly upon pair housing. Furthermore, we identified distinct behavioral and biological traits which predict future rank in paired mice. Notably, subordinate animals expressed more exploratory but not anxiety behaviors and higher FCM status at baseline, while prioritizing novelty exploration in the 3CSA. This is similar to male hierarchies, in which subordinates engage in patrolling behavior. To our knowledge, this trait has not been demonstrated in females.

Post-SI, the lack of a sucrose preference in dominants is interesting when compared to the deterioration in CSS, higher FCM and diminished exploratory behavior demonstrated by subordinates. This indicates that subordinates become more stress-responsive after SI, whereas dominants become anhedonic. An alternative interpretation is that subordinates consume more sucrose in response to stress, similar to ‘binge-eating’ behavior. These findings collectively demonstrate a distinction between stress and anxiety, and indicate an integrated, adaptive function for rank, stress status and role assignment.

The next aim examines the influence of rank on vulnerability to psychosocial stress produced by an unstable social environment. A cohort of adult female C57/Bl6J mice (n = 36) is currently undergoing 7 weeks of SIS, in which cage mates are randomized every 3 days to disrupt hierarchies as they become established. CE is performed during SIS to identify rank, and FCM is taken. After, mice will undergo behavioral testing for anxio-depressive phenotypes and changes in attention and cognition.

Keywords: Social Behavior, Anxiety and Depression, Females, Social Stress, Social Dominance

Disclosure: Nothing to disclose.

P310. Increased Effort Expenditure in Major Depression Following a TNF-Alpha Antagonist is Mediated by Change in Systemic Immunometabolism

Sarah Etuk, Emma Hahn, Brittany DeVries, Jessica Cooper, Nadia Irfan, Dannielle Harrison, Makiah Nuutinen, Asim Lal, Amanda Arulpragasam, Shabnam Hossein, Bobbi Woolwine, Ebrahim Haroon, Jennifer Felger, Andrew Miller, Michael Treadway*

Emory University, Atlanta, Georgia, United States

Background: Evidence suggests that increases in inflammation and alterations in systemic immunometabolism may contribute to the pathophysiology of motivational anhedonia in major depressive disorder (MDD). MDD patients have been shown to exhibit elevated levels of peripheral blood inflammatory biomarkers, particularly C-reactive protein (CRP), tumor necrosis factor (TNF)-alpha, interleukin-6 (IL-6), and IL-1-beta, which have in turn been linked to motivational deficits in both animals and humans. Specifically, stimulation of cytokines has been shown to reduce willingness to expend effort for rewards. Further, these effects have been found to be strongest in patients with both high inflammation and altered protein and genomic signaling within pathways related to glucose metabolism. These metabolic changes have been hypothesized to reflect an increased reliance on glycolysis (as opposed to oxidative phosphorylation) within activated immune cells. Taken together, these data raise the possibility of an immunometabolic-dependent pathway that contributes to the development of motivational anhedonia for depressed patients with high inflammation. To date, however, only a few studies have explored the impact of pharmaceuticals that target inflammation on motivational anhedonia in depressed patients. Here, we present novel results from a newly completed study (NCT03006393) aimed at identifying the mechanisms by which inflammation and immunometabolism contribute to motivational anhedonia in depressed patients.

Methods: Effort-based decision-making and peripheral inflammatory markers were assessed in 60 patients with current MDD at a baseline session, after which 37 patients with CRP > 3 mg/L were randomized to receive a single infusion of either the TNF-alpha antagonist infliximab (5mg/kg) or saline solution as part of a double-blind, placebo-controlled, randomized clinical trial. Motivated behavior was using an effort-based decision-making task (EBDM) during which participants made a series of choices about how much physical effort (rapid button presses) they were willing to expend in exchange for varying amounts of monetary reward. Effort discounting was assessed by examination of choices at each effort level (20%, 50%, 80%, or 100% of a participant’s maximum press rate) as well as by a well-validated computational model. For this model, a free parameter ‘k’ is fit to each participant’s choices and represents the extent to which effort reduces the value of reward. Plasma samples were also collected at each time point, and were assayed for TNF soluble receptor II (TNFRII) and five markers of systemic glucose metabolism: adiponectin, resistin, leptin, glucose, and insulin. These six markers were combined to form a composite measure of TNFRII and glucose metabolism.

Results: At baseline, the overall proportion of effortful choices as well as the k discounting parameter were associated with measures of anhedonia and fatigue, including the apathy-motivation index, and the anhedonia subscale from the IDS-SR (ps < .05). Following randomization, there was a significant treatment X time interaction for TNFRII with a reduction for patients receiving infliximab relative to placebo (p = 0.024), but not glucose metabolism. We also observed a significant group by time interaction such that patients receiving infliximab showed a decrease in effort discounting (lower k parameter) relative to placebo (p = 0.045). We also observed a treatment by time by effort interaction (p < .05) such that this effect was most pronounced at the higher levels of effort (80% and 100%). Further, we observed that post-infusion decreases in plasma TNFRII and glucose metabolism predicted increases in effortful choices at the highest effort level (controlling for age and sex, p = 0.009) as well the k discounting parameter (p = 0.033). Finally, a bootstrapped mediation analysis found that change in plasma TNFRII and glucose metabolism significantly mediated the relationship between treatment assignment (infliximab or placebo) and change in effortful choice (p < 0.05).

Conclusions: The results of the study indicate that administration of the anti-inflammatory agent infliximab to patients with current MDD and high inflammation increases the willingness to expend effort, a hallmark of motivational anhedonia. Moreover, this effect appears to mediated by changes in markers of TNF signaling in combination with markers of glucose metabolism. These results highlight the potential for the combination of inflammatory and immunometabolic biomarkers and anti-inflammatory treatment strategies to identify and treat motivational impairments.

Keywords: Precision Medicine for Mood Disorders, Immune Modulation, Effort Based Decision Making Task, Anhedonia, Computational Models of Decision-Making

Disclosure: Blackthorn Therapeutics: Consultant (Self)

P311. Zelquistinel (GATE-251): Results of a Phase 1 Single Ascending Dose Study to Evaluate the Safety, Pharmacokinetics, and EEG Effects of a Novel Rapid Acting, Orally-Bioavailable NMDA Receptor Modulator

John Donello*, Jeffrey Burgdorf, Kirk Bertelsen, Leonardo Terjo, Roman Rosipal, Joseph Moskal, Ronald Burch, Anantha Shekhar

Gate Neuroscience, San Clemente, California, United States

Background: Major depressive disorder (MDD) is a common disabling and potentially life-threatening condition estimated to affect > 300 million people worldwide. Glutamatergic mediated plasticity and modulation of NMDA receptor activity have been employed in developing rapid-acting treatments for MDD. GATE-251 (also known as AGN-251751) is a NMDA receptor modulator that binds to a unique site on the receptor. In animals, zelquistinel has oral bioavailability greater than 90%, and provides efficacy in several animal models of depressive-like behavior. This Phase 1 first-in-man study evaluated safety, pharmacokinetics and GATE-251 as well as EEG measures of NMDAR activation in healthy volunteers.

Methods: This double-blind, randomized, placebo-controlled study evaluated healthy male or female subjects aged 18-55 years, with supine heart rate of 50-100 bpm who used no other drugs for at least 14 days prior to this study and were negative in drug of abuse screens. Part A of the study evaluated safety, plasma pharmacokinetics and EEG following single fasting doses of 100 microg, 1 mg, 3 mg, 10 mg, 25 mg, or 50 mg GATE-251 as an oral solution, compared to a water placebo (randomization 6:2 drug:placebo). A separate group studied a 1 mg dose in female subjects. Part B evaluated safety and CSF pharmacokinetics of single doses of 1 mg or 10 mg fasted and 1 mg fed (N = 5, 3, 3) in subjects with indwelling lumbar catheters. Part C evaluated plasma PK in fasted male subjects compared to subjects who received a high-fat breakfast (N = 5, 3).

Results: Safety: In this study no serious adverse events were reported, nor were any clinically significant changes in plasma chemistry, hematology or urinalysis observed. No subjects experienced clinically significant changes in vital signs or ECG. There were no treatment emergent psychotomimetic symptoms (as measured by changes in C-SSRS, BPRS + or CADSS) from predose baseline to end of study. Treatment-related adverse events (TRAEs) were few: in Part A (N = 14 placebo, N = 42 GATE-251) there were no TRAEs in the placebo group and 1 in the 1 mg GATE-251 group: headache. In Part B (N = 4 placebo, N = 12 GATE-251), there were no TRAEs in the placebo group and 2 in the 10 mg group: 1 lumbar puncture syndrome, 1 disturbance in attention. In Part C (N = 0 placebo, N = 6 GATE-251), there were no TRAEs.

Pharmacokinetics: In Part A, GATE-251 exhibited rapid absorption and dose-related increases in exposure assessed as Cmax or AUC. T1/2 was similar across doses at 0.5 hr, and was not different in male vs female subjects. In Part B, transport into the CSF was significant, with a Tmax of 4 h. Too few sampling times prevented calculation of T1/2 in CSF. A high fat meal slowed absorption of GATE-251 compared to fasted, with reduced Cmax exposure, although AUC exposure was not affected.

EEG: GATE-251 increased resting alpha EEG power, indicative of effective central modulation and enhanced NMDAR activation. While Gate-251 induced alpha power showed an inverted U-shaped dose response relationship at higher doses, doses that optimally enhanced alpha EEG demonstrated CSF drug concentration that corresponded to concentrations that enhance NMDAR activity in vitro.

Conclusions: GATE-251 was well-tolerated oral NMDA modulator with few treatment-related AEs. There was no evidence of psychotomimetic effects over the dose range evaluated. GATE-251 was rapidly absorbed into the plasma and exposure was dose-related. No gender-associated differences were observed. In plasma, AUC exposure was not affected by a high fat meal whereas in CSF AUC exposure appeared to be enhanced. The CSF levels achieved within this dose range were robust and corresponded the concentrations necessary to modulate NMDA receptors in vitro. Translational pharmacodynamics of qEEG/ERPs and the plasma/CSF pharmacokinetics demonstrate that the assessed doses meet and/or exceed drug concentrations that are predicted to be maximally efficacious in humans.

Keywords: Fast-acting Antidepressant, NMDA Glutamate Receptors, Translational Approaches to Drug Development, Synaptic Plasticity

Disclosure: Gate Neurosciences, Anagin, Vasculonics, MindX: Founder (Self)

Karuna Therapeutics: Advisory Board(Self)

Johnson and Johnson: Grant (Self)

P312. Target Trial Emulation: Evaluating a Treatment for Metabolic Depression

Katie Watson Lin, Caleb Spiro, Kayla Carta, Alison Myoraku, Natalie Rasgon*

Stanford University School of Medicine, Palo Alto, California, United States

Background: Previous evidence suggests that pioglitazone, an insulin-sensitizing medication, in patients with major depressive disorder (MDD) and insulin resistance (IR) can be useful in ameliorating non-remitted MDD. To investigate this claim, we conducted two emulated target trials (ETTs) of the effect of adjuvant pioglitazone on antidepressant response among people with type 2 diabetes (DM2). Pioglitazone was compared to two other classes of non-insulin sensitizing DM2 medications, sulfonylureas and dipeptidyl peptidase 4 (DPP4) inhibitors. It was hypothesized that the combination of antidepressant medication and pioglitazone would elicit a superior antidepressant treatment response compared to adjuvant DPP4 inhibitors or sulfonylureas over a one-year follow-up period.

Methods: The two ETTs were designed using health insurance claims from the Optum Clinformatics® Data Mart version 3.0 (Optum) (Optum Insight, Eden Prairie, MN). Poorer antidepressant response was measured by an increase of new prescriptions for antidepressants one year after the study start date. A treatment was defined as new if it had never been prescribed, or if it had not been prescribed for at least one year plus the number of days’ supply of the most recent prescription.

Results: The participants in ETT1 who took pioglitazone (n = 1308) were more likely to be younger, male, and use statin medications when compared to users of DPP4 inhibitors (n = 1634). In ETT2 pioglitazone users (n = 1,639) were more likely to take statins, use insulin, and take a greater average of antidepressant medications in the prior year compared to those who used sulfonylureas (n = 4,879). After matching, the standardized mean difference for all covariates in both ETTs was <0.15, with exception of age for ETT1 (SMD = 0.17). In ETT1, instrumental variable analysis found that pioglitazone users added a new antidepressant or antipsychotic treatment 1.3 times compared to 1.7 times among DPP4 users over a 1-year follow-up period. In ETT2, similar analysis found that pioglitazone users added a new antidepressant or antipsychotic treatment 0.8 times compared to 1.4 times among DPP4 users over a 1-year follow-up period.

Conclusions: These findings lend evidence to the hypothesis that adjuvant pioglitazone lead to a stronger antidepressant treatment response than sulfonylureas or DPP4 inhibitors among individuals with MDD and DM2 - as measured by fewer treatment shifts and/or additions of a new antidepressant or antipsychotic. Coupled with previous evidence on the role of pioglitazone in MDD patients with IR, this evidence suggests that pioglitazone may prove useful in ameliorating treatment MDD response among people with comorbid DM2.

Keywords: Major Depressive Disorder, Emulated Target Trial, Insulin Resistance

Disclosure: Nothing to disclose.

P313. Go/NoGo EEG Data Associations Depression Severity in Depressed and Suicidal Patients

Julianne Mirmina, Diane Kim, Jessica Carbajal, Andrew Deptula, Ricardo Caceda*

Stony Brook University, Stony Brook, New York, United States

Background: Impaired inhibition has been observed in depressed and suicidal patients. The Go/NoGo task assesses cognitive and motor inhibition, as well as behavioral control. Increased average amplitude of event-related potentials (ERPs) is linked to increased behavioral control and healthier levels of brain activity. In this study, we aimed to examine the mean ERPs associated with successful response inhibition and its relationship with depression severity and suicide risk.

Methods: Three groups of adult depressed patients of both genders: i) after a suicide attempt in the past 72 hours (n = 6); ii) currently endorsing suicidal ideation (n = 10); and iii) non-suicidal (n = 9). Participants subjects underwent an electroencephalogram (EEG) while participating in a Go/NoGo task during 420 trials. EEG data was recorded utilizing the ActiveTwo BioSemi system, using a 34 electrode mesh. Participants were instructed to press a mouse button when the arrow was oriented vertically (without tilt, n = 340) and not to press the button when the arrow was tilted (15 degrees tilt, n = 80). EEG mean ERP amplitude during the correct NoGo trials.

Results: There were no ERP activity differences between groups. ERP activity recorded during the correct NoGo stimuli was positively correlated with depression severity (p = 0.016), with a non-significant trend with age (p = 0.052).

Conclusions: Cognitive inhibition was correlated with depression severity and age, rather than with suicide risk status in adult depressed suicidal patients.

Keywords: Suicide, EEG, Behavioral Inhibition

Disclosure: Neurostar: Grant (Self)

P314. Theta-Gamma Coupling Vs Clinical Diagnosis in Separating Older People With Mild Cognitive Impairment With or Without Major Depressive Disorder on Cognitive Function

Heather Brooks, Wei Wang, Reza Zomorrodi, Daniel Blumberger, Christopher Bowie, Zafiris Daskalakis, Corinne Fischer, Alastair Flint, Nathan Herrmann, Sanjeev Kumar, Krista Lanctot, Linda Mah, Benoit Mulsant, Bruce Pollock, Aristotle Voineskos, Tarek Rajji*

University of Toronto, Toronto, Canada

Background: Individuals with mild cognitive impairment (MCI) and major depressive disorder (MDD), including when MDD is in remission, are at higher risk for cognitive decline and Alzheimer’s dementia (AD) than those with either diagnosis alone. Prefrontal cortex theta-gamma coupling (TGC) may be an early marker of prefrontal cortical dysfunction. The aim of this study was to determine whether TGC can discriminate individuals’ cognitive performance better than their diagnosis (i.e., MCI vs. MCI + MDD). We hypothesize that TGC at a specific cut-off will create more distinct groups with regard to global cognition than clinical diagnoses.

Methods: We analyzed baseline data from 128 participants with MCI (mean age: 71.8, SD: 7.3) and 85 with MCI + MDD (mean age: 70.9, SD: 4.7) who are participating in a dementia prevention trial (NCT02386670). Participants with MDD were in remission. Participants with MDD were in remission. Participants were assessed clinically and cognitively with a comprehensive neuropsychological battery. TGC was measured during the performance of a working memory task, the N-back. We determined a sample-derived TGC cut-off using performance on the 2-back condition among 50% of our sample (training sample, randomly selected). We then tested that cut-off on the other 50% of the sample (validation sample), to examine how the cut-off separated individuals on global cognition as ascertained using a composite global cognitive measure from the neuropsychological battery. Both of these steps were repeated 1000 times to generate stable estimates of the differences between groups. We compared the Cohen’s d between the TGC groups and the diagnostic groups.

Results: Cohen’s d for the TGC groups (Cohen’s d = 0.31) was larger than the Cohen’s d for the diagnostic groups (Cohen’s d = 0.13). There were no significant differences in performance on any of the cognitive domains between the MCI and MCI + MDD groups. In contrast, the high vs. low TGC groups differed significantly in terms of global cognition (t(210) = -2.45, p = 0.02), processing speed (t(207.9) = -2.78¸ p = 0.006), working memory (t(210) = -2.91, p = 0.004), and executive function (t(209) = -2.04, p = 0.04).

Conclusions: Global cognition differed in groups based on low vs. high TGC but not in groups based on MCI vs. MCI + MDD diagnosis. The TGC groups (but not the diagnostic groups) also differed in terms of cognitive domains depending on prefrontal cortex. Our results suggest that TGC might be an early marker of prefrontal cognitive dysfunction. Future work should focus on determining if individuals with low TGC are at an increased risk for cognitive decline and progression to AD.

Keywords: EEG Biomarkers, Mild Cognitive Impairment Due to AD, Major Depression Disorder

Disclosure: Nothing to disclose.

P315. No Meaningful Opioid Abuse Liability of REL-1017 (Esmethadone; D-Methadone), a Rapid-Acting Antidepressant in Clinical Development: A Human Abuse Potential Study

Jack Henningfield*, Glen Apseloff, Charles Gorodetsky, Marco Pappagallo, Megan Shram, Sara De Martin, Reginald Fant, Frank Vocci, Frank Sapienza, Thomas Kosten, Jeff Huston, August Buchhalter, Judy Ashworth, Ryan Lanier, Franco Folli, Sergio Traversa, Charles E. Inturrisi, Paolo L. Manfredi

Pinney Assoc and Johns Hopkins University School of Medicine, Bethesda, Maryland, United States

Background: Opioid abuse is widespread, with an estimated 57,550 overdose deaths from synthetic opioids in the U.S. in 2020. REL-1017, a promising, rapid-acting, antidepressant candidate, is the dextrorotary isomer of methadone (esmethadone; d-methadone). Although previous studies indicate that d-methadone is opioid inactive and lacks meaningful abuse potential, its close chemical similarity to the opioid-active isomer l-methadone prompted further evaluation. Therefore, we performed a human abuse potential (HAP) study using current state-of-the art methodology to further ascertain the abuse liability of REL-1017.

Methods: The study was a single-dose, randomized, double-blind, double-dummy, active- and placebo-controlled, 5-way crossover HAP study of REL-1017 in experienced recreational drug users. The study consisted of 4 phases: Screening, Qualification, Treatment, and Follow-up. Within 28 days of Screening, eligible subjects participated in a 4-day Qualification Phase to ensure that they were able to discriminate the effects of the positive control, oral oxycodone 40 mg, when compared to placebo. During Qualification, all subjects underwent a naloxone challenge test to confirm that they were not opioid-dependent. Qualified subjects entered the Treatment Phase. During the Treatment Phase, composed of 5 treatment periods, each subject received the following oral treatments in a randomized, double-blind, double-dummy, crossover fashion with >11 days of washout between treatments: REL-1017 25 mg (25R)(proposed therapeutic daily dose), REL-1017 75 mg (75R)(proposed loading dose), REL-1017 150 mg (150R)(maximum tolerated dose), oxycodone 40 mg (OX)(standard active control), and placebo (PL). Subjects then completed a safety follow-up approximately 1 week after the last treatment. The primary endpoint of this study was the maximum effect (Emax) for Drug Liking (“at this moment”), assessed with a bipolar (0 to 49 = dislike; 50= neutral; 51-100 = like) visual analog scale (VAS). The key secondary endpoints were VAS for Overall Drug Liking and for Take Drug Again. The primary treatment comparisons to assess the abuse potential of REL-1017 included oxycodone versus placebo (study validity), REL-1017 versus oxycodone, and REL-1017 versus placebo, using the primary endpoint (Drug Liking VAS Emax). Data were analyzed using a one-sided Student’s t test for paired data for oxycodone vs. REL-1017, and using equivalence margins: oxycodone vs. placebo (□ = 15) and REL-1017 vs. placebo (□ =11). Statistical analyses were performed on “modified completers”, defined as subjects completing all 5 treatments, and excluding subjects with similar Drug Liking Emax scores (<5 points difference) across all study treatments or subjects with an Emax for placebo >60 and ≤5 difference between Emax for oxycodone and placebo.

Results: A total of 50 subjects were randomized; 3 subjects did not complete all 5 treatments, and 3 subjects did not fulfill criteria for “modified completers.” A total of 44 subjects fulfilled the criteria for “modified completers” and were evaluated in the statistical analyses. The mean age of the 44 “modified completers” was 36.6 (SD 9.24); 8 (18.2%) subjects were females, and 36 (81.8%) were males. The mean and median Emax for the five drug conditions are shown below.

Mean

PL: 51.7

25R: 53.0

75R: 58.2

150R: 64.9

OX: 85.0

Median

PL: 50.0

25R: 50.0

75R: 50.0

150R: 58.0

OX: 89.0

P-value vs. OX

<0.001

<0.001

<0.001

<0.001

 

P-value vs. PL

 

<0.001

<0.001

<0.10

 

The Emax for 40 mg oxycodone was significantly greater than placebo, confirming study validity, and it was greater than all 3 doses of REL-1017, also with a high degree of statistical significance. Consistent, statistically significant differences between all tested doses of REL-1017 and oxycodone were seen for the two key secondary endpoints (“Overall Drug Liking” and “Take Drug Again”). Comparison of REL-1017 to placebo using the FDA suggested equivalence margin analysis indicated similarity to placebo at p < 0.001 for the 25 mg and 75 mg doses of REL 1017 and at p < 0.10 for the 150 mg dose.

Conclusions: REL-1017 doses of 25 mg (daily therapeutic dose), 75 mg (loading dose) and 150 mg (maximum tolerated dose and 6X the daily therapeutic dose) exhibited at least a 20-point difference in Emax Drug Liking compared to 40 mg oxycodone with a highly significant difference (p < 0.001). The similarity of 25 mg and 75 mg doses of REL-1017 to placebo were also highly significant (p < 0.001), with similarity of 150 mg REL-1017 to placebo at p < 0.1. Low-level liking is commonly seen in HAP studies at high doses of the test substance and is consistent with unscheduled substances and with controlled substances in U.S. DEA Schedule V or IV. While DEA scheduling of new molecules is based on the analysis of multiple factors, including in vitro studies, animal studies, and human studies, the current HAP study design is considered the single most predictive and important study to determine abuse potential. This study showed no meaningful opioid abuse potential for REL-1017 in healthy recreational opioid users. Ongoing Phase 3 trials to confirm the efficacy and safety of REL 1017 are registered with ClinicalTrials.gov (NCT03051256).

Keywords: REL-1017, Antidepressant, Abuse Potential Study

Disclosure: Pinney Associates: Consultant (Self)

P316. Stress During Adolescence, Inflammatory Status and Depression Vulnerability: Potential Role of the Gut Microbiome

Annamaria Cattaneo*, Nicola Lopizzo, Moira Marizzoni, Monica Mazzelli, Stefania Provasi, Veronica Begni, Marco Andrea Riva

University of Milano, Italy

Background: Exposure to early adverse experiences induces persistent changes in physiological, emotional and behavioral functions predisposing the individual to an enhanced vulnerability to develop different psychiatric disorders during lifespan. The adverse outcomes depend upon the timing of the stressful experiences, and in this contest, adolescence represents a key sensitive period for brain development. Among the biological systems involved, the gut microbiota has recently been proposed to act on the interplay between the stress response, brain functions and immune system, through the gut-brain axis communication.

Methods: We used a combined preclinical and clinical approach. At preclinical level we used the model of social isolation in rats during adolescence, based on the lack of all social contacts, for four weeks after weaning, followed by re-socialization until adulthood. We collected fecal samples at different post-natal days to investigate the short- and long-lasting effects of social isolation on gut microbiota composition by running the 16S metagenomics sequencing and we collected brain areas (dorsal and ventral hippocampus and prefrontal cortex) samples at killing to measure a panel of inflammatory and microglia activation markers by Real Time PCR. Both male and female animals were analyses. To evaluate the impact of stress on depression vulnerability and to identify possible peripheral biomarkers blood samples from a group of adolescents exposed to childhood trauma and also characterised for depressive symptoms have been tested for transcriptomic analyses (by running both GeneAtlas and RNAseq techniques).

Results: 16S metagenomics sequencing analysis revealed that microbial changes were influenced by age in both isolated and controls rats, regardless of sex, whereas social isolation impacted the microbial composition in a sex-dependent manner. A multivariate analysis was used to identify stress-related genera associated with social isolation condition. In brain areas we found a specific inflammatory pattern, in dorsal and ventral hippocampus, that significantly correlated with gut microbiota composition, with a more pronounced effect in male animals. In particular, SI female rats showed significant increased expression of TGFβ (+30%, p = 0.039) in the dorsal hippocampus and of IL1β and IL6 in the ventral hippocampus (+31% and +38%, p < 0.044) compared to CTRL animals (Fig. 3 and Supplementary fig. 4). SI male rats reported increased expression of MIF and TGFβ (+91% and +45%, p < 0.015) in the dorsal hippocampus and IL1β and IL6 in the ventral hippocampus (+53% and +41%, p < 0.005) compared to controls. Regarding microglia activation markers, social isolated male rats showed a significant increased expression of IBA1, CX3CL1, CX3CR1, CD40 and CD68 compared with controls in dorsal hippocampus (+57%, +72%, +61%, +61%, +56%, p < 0.014) as well as increased expression of CD40 ( + 21%, p < 0.049) in the ventral hippocampus. In females, SI-related genera were associated with inflammation primarily in the ventral hippocampus. In particular, the association involved IL1beta, IL6 and all but CD68 for the microglial activation biomarkers (|rho | > 0.64, p < 0.096). In males, the association of SI-related genes with inflammation were comparable in both dorsal and ventral hippocampus and mainly involved the genera Christensenellaceae R-7 group (|rho | > 0.68, p < 0.090).

Transcriptomic analyses in blood samples of adolescents (males and females) revealed alterations in several pathways related to the immune system, with an effect that was driven by male and not female adolescents.

Conclusions: Overall, we reported a novel sex-specific association between gut microbiota composition and inflammatory response related to social isolation paradigm during adolescence. A more pro-inflammatory status was also observed in a group of adolescents that were exposed to childhood trauma and that developed depression, with an effect that, similarly to the animal model, was more pronounced in males. This overall suggests that stressful experiences early in life could have a long-lasting impact on the development of the immune system, of the gut microbiome and of their interplay, that could in turn influence the vulnerability to develop mental disorders later in life.

Keywords: Early Life Stress, Adolescence, Depression, Inflammation, Gut Microbiome

Disclosure: Nothing to disclose.

P317. Sex Influences the Effects of Social Status on Socioemotional Behavior and Serotonin Neurochemistry in Rhesus Monkeys

Alison Wakeford, Jonathon Nye, Dene Voisin, Kim Huhman, Elliott Albers, Vasiliki Michopoulos*

Emory University, Atlanta, Georgia, United States

Background: Sex differences in the prevalence rates of many psychiatric disorders highlight the importance of including sex as a biological variable in animal studies focused on understanding mechanisms underlying psychopathology. One translational animal model that has been leveraged to understand the impact of chronic psychosocial stress exposure on behavioral health is social subordination in rhesus macaques. Hierarchical dominance relationships maintained by agonistic interactions govern social interactions in rhesus monkeys, similar to many other mammalian species. Importantly, social dominance is associated with resistance to the physiological consequences of social stress while social subordination is associated with vulnerability to stress-related, adverse phenotypes. While serotonergic pathways play a critical role in the etiology and treatment of stress-related psychiatric conditions, the contribution of biological sex in these processes remain unclear. Thus, the current study was designed to assess sex differences in the effects of social status on socioemotional behavior and serotonin neurochemistry in socially housed rhesus monkeys. We hypothesized that sex and social status interact to influence socioemotional behaviors as well as 5HT1A receptor binding potential (5HT1A-BP) in regions of interest (ROIs) implicated in the regulation of aggressive, affiliative, and anxiety-like behaviors.

Methods: Gonadally intact adult female (n = 14) and male (n = 13) rhesus monkeys housed in small social groups of three to six monkeys each were subjects in the current study (6 dominant and 8 subordinate females; 6 dominant and 7 subordinate males). Behavioral observations were collected for each group using a standard monkey ethogram over five weeks to capture rates of aggression, submission, affiliation, and anxiety-like behavior. A positron emission tomography (PET) scan for 5HT1A receptor binding potential was conducted using 4-(2′-Methoxyphenyl)-1-[2′-(N-2′′-pyridinyl)-p[18F]fluorobenzamido]ethylpiperazine (MPFF). Structural MR images were obtained within three weeks of the PET scan for co-registration to assist in region placement and evaluation of white matter volumes. ROIs included sub-regions of the prefrontal cortex (PFC), the hypothalamus, the dentate gyrus of the hippocampus, and the dorsal raphe nucleus (DRN). The Emory University Institutional Animal Care and Use Committee approved all procedures in accordance with the Animal Welfare Act and the U.S. Department of Health and Human Services “Guide for Care and Use of Laboratory Animals.” ANOVAs were used to determine the effects of sex (males vs. female), social status (dominant vs. subordinate), and their interaction on socioemotional behaviors and 5HT1A-BP. Post-hoc analyses were conducted when necessary and significance was set at p ≤ 0.05 for all tests.

Results: Submission was significantly greater in subordinate versus dominant animals (F = 11.637, p = 0.003), regardless of sex (F = 1.006, p = 0.327). Aggression was not impacted by sex, status, or their interaction (p’s > 0.05). Rates of affiliation were impacted by an interaction of sex and status (F = 4.243, p = 0.05). Dominant females engaged in more affiliation than did dominant males (F = 10.134, p = 0.004). Anxiety-like behavior was significantly greater in females than in males (F = 6.909, p = 0.015), regardless of social status (F = 0.122, p = 0.122). Structural MRIs showed that the ROI volumes were significantly larger in males than in females (p’s < 0.05), except for the DRN (p > 0.05). Because of these sex differences, further analyses assessing impacts of sex, status, and their interaction on 5HT1A-BP were adjusted for age and structural volume of ROI. 5HT1A-BP in the straight gyrus was significantly greater in females than in males (F = 4.937, p = 0.037) regardless of social status (F = 0.381, p = 0.544). Hypothalamic 5HT1A-BP was also significantly greater in females than in males (F = 26.989, p < 0.001), regardless of social status (F = 1.590, p = 0.221). 5HT1A-BP in the dentate gyrus of the hippocampus was significantly impacted by a sex by status interaction (F = 5.862, p = 0.025). 5HT1A-BP in the dentate gyrus was greater in dominant compared to subordinate females (p = 0.027) but was not different between dominant and subordinate males (p = 0.569). There were no effects of sex, status, or their interaction on 5HT1A-BP in the DRN (p’s > 0.05).

Conclusions: Taken together, the current data show that sex impacts the effects of social status on socioemotional behavior and 5HT1A-BP in ROIs implicated in the regulation of aggressive, affiliative, and anxiety-like behaviors in rhesus monkeys. These data have important implications for the treatment of stress-related behavioral health outcomes, as they suggest that sex and social status are important factors to consider in the context of serotonergic drug efficacy.

Keywords: Sex Differences, Social Status, Serotonin 1A Receptors, Behaviors

Disclosure: Nothing to disclose.

P318. Using Machine-Learning on Proteomics and Lipidomics Data to Improve Individual Prediction of Chronicity in Major Depressive Disorder

Philippe Habets, Rajat Thomas, Guido van Wingen, Brenda Penninx, Onno Meijer, Christiaan Vinkers*

Amsterdam University Medical Center, Amsterdam, Netherlands

Background: Depressive disorder is a heterogenous condition that differs widely in both therapy response and prognosis. The ability to individually predict disease course early on is essential for optimal treatment planning. Here, we use a data-driven machine learning approach to test the potential of combining two sets of -omics data in addition to easy-to-acquire clinical baseline variables for the prediction of two-year chronicity in major depressive disorder.

Methods: Proteomics (243 analytes) and lipidomics (231 variables) assays were performed on whole blood serum at baseline in patients with baseline depression (n = 611 for proteomics, n = 790 for metabolomics, n = 608 for combined data) from the NESDA cohort (1). Two classes of outcome (two-year chronicity or remission) were balanced (49% vs 51%) and showed no significant differences in possible confounding factors (age, gender, bmi, years of education, antidepressant use at baseline, months of antidepressant use between baseline and follow-up). XGboost implementation in R was used with an 80-20 train-test split. An inner 10 times repeated 10-fold cross validation loop was used to optimize hyperparameters, mitigate overfitting issues and select for the best generalizable model (1000 hyperparameter-grid combinations were used) in the train set. Final models using a) clinical, psychological, and demographical data only (10 variables), b) added proteomics data and c) added lipidomics data were tested on an outheld test set and evaluated by their respective AUROC. Variable importance analysis was performed using SHAP (2).

Results: Using non-biological data only, our model was able to predict two-year chronicity (AUROC = 0.63, accuracy = 63%.) Addition of proteomics yielded substantially increased predictive performance (AUROC = 0.75, accuracy = 67%). Using lipidomics in combination with the non-biological data resulted in low predictive value (AUROC = 0.57, accuracy = 53%). Adding proteomics data to the lipidomics and non-biological data slightly increased model performance, but still showed poor performance (AUROC = 0.59, accuracy = 58%). The proteomics-only trained model showed comparable performance metrics to the proteomics and clinical variables trained model (AUROC = 0.73, balanced accuracy = 70%). Variable importance analysis indicated that combining clinical with protein data resulted in a different ranking of the most predictive proteomic analytes compared to the proteomics-only model. For the model trained on both proteomic and non-biological data, symptom severity was the most important predictor, followed by proteomic analytes involved in hemostasis and the immune system. Repeated analysis on proteomics data only with a penalized logistic regression model (elastic net) showed lower performance and limited overlap of most important variables, indicating the importance of detection of non-linear patterns in the included biological data.

Conclusions: Proteomics but not lipidomics data were able to augment the performance of clinical variables regarding chronicity of Major Depressive Disorder 2 years later. Even though the model that used a combination of proteomics and clinical variables showed good performance (AUROC = 0.75), improvement in accuracy and feasibility of data-acquirement are needed to warrant clinical implementation.

References:

1. Penninx BWJH, Beekman ATF, Smit JH, et al. The Netherlands Study of Depression and Anxiety (NESDA): rationale, objectives and methods. Int J Methods Psychiatr Res. 2008;17(3):121-140. https://doi.org/10.1002/mpr.256

2. Lundberg SM, Erion G, Chen H, et al. From local explanations to global understanding with explainable AI for trees. Nat Mach Intell. 2020;2(1):56-67. https://doi.org/10.1038/s42256-019-0138-9

Keywords: Biomarker Prediction, Machine Learning, Proteomics

Disclosure: Nothing to disclose.

P319. Effect of Lumateperone (ITI-007) on Quality of Life and Functional Disability in the Treatment of Bipolar Depression

John Edwards*, Suresh Durgam, Susan Kozauer, Robert Davis, Sharon Mates, Rakesh Jain, Roger McIntyre

Intra-Cellular Therapies, Inc., Woodside, New York, United States

Background: People with bipolar disorder have a more impaired quality of life and functional disability compared with both the general population and those with other mood or anxiety disorders. Residual symptoms of depression account for a greater degree of reduced quality of life than symptoms associated with hypomania or mania in patients living with bipolar disorder. Lumateperone (lumateperone tosylate, ITI-007), a mechanistically novel antipsychotic that simultaneously modulates serotonin, dopamine, and glutamate neurotransmission, is FDA-approved for the treatment of schizophrenia and is currently being investigated for the treatment of bipolar depression

In a recent phase 3 clinical trial (Study 404, NCT03249376) in people with bipolar I or bipolar II disorder experiencing a major depressive episode (MDE, bipolar depression), lumateperone 42 mg monotherapy significantly improved symptoms of depression compared with placebo. This analysis of Study 404 investigated improvements in functional disability and quality of life as measured using the prespecified secondary outcome measure the Quality of Life Enjoyment and Satisfaction Questionnaire-Short Form (Q-LES-Q-SF). In addition, a post hoc analyses looked at the individual items of the Q-LES-Q-SF.

Methods: Patients in this study (18–75 years) had a confirmed diagnosis of bipolar I or bipolar II disorder based on Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) criteria. Participants had to be experiencing an MDE (Montgomery-Åsberg Depression Rating Scale [MADRS] Total score ≥ 20 and Clinical Global Impression Scale-Bipolar Version-Severity [CGI-BP-S] score ≥ 4). Patients were randomized to receive lumateperone 42 mg or placebo orally, once daily in the evening for 6 weeks. The primary endpoint was the change from baseline to Day 43 in MADRS Total score, analyzed using a mixed-effects model for repeated measures (MMRM) approach in the intent-to-treat (ITT) population.

The Q-LES-Q-SF, a measure of quality of life and aspects of function, evaluates patient satisfaction with quality of life using a 5-point rating scale (from 1 [very poor] to 5 [very good]). This post hoc analysis evaluated the mean change from baseline to Day 43 in the Q-LES-Q-SF individual item scores using an analysis of covariance with last observation carried forward (ANCOVA-LOCF) in the ITT population. An ANCOVA-LOCF was also used to analyze the psychosocial factor composed of items 2 (mood), 4 (household activities), 5 (social relationships), 6 (family relationships), 7 (leisure time activities), 8 (ability to function in daily life), 9 (sexual drive, interest and/or performance), 10 (economic status), 11 (living/housing situation), and 14 (overall sense of well-being) and the physical factor composed of items 1 (physical health), 12 (get around physically without dizziness), and 13 (vision in ability to do work).

Results: The ITT population comprised 376 patients (lumateperone 42 mg, 188; placebo, 188). Mean baseline MADRS Total score and CGI-BP-S depression subscore of 30.6 and 4.6, respectively, indicate the ITT population had moderate-to-severe depression symptoms at baseline. Patients in the lumateperone 42-mg group had significantly greater mean improvement on MADRS Total score change from baseline to Day 43 compared with placebo (least squares mean difference vs placebo [LSMD], − 4.585; 95% confidence interval [CI], − 6.344 to −2.826; effect size vs placebo [ES], − 0.56; P < .0001). Lumateperone 42-mg treatment significantly improved Q-LES-Q-SF Total score from baseline to Day 43 compared with placebo (LSMD, 2.9; 95% CI, 1.15 to 4.59; P = .001). There were significant improvements at Day 43 with lumateperone vs placebo for the Q-LES-Q-SF psychosocial factor (ES, + 0.38; P = .0005); differences vs placebo did not reach statistical significance in the physical factor (ES, + 0.20; P = .0627).

The Q-LES-Q-SF items with the lowest mean scores at baseline (very poor to poor ratings) suggested that the domains that were the most impaired in patients with bipolar depression were mood (lumateperone, 1.8; placebo, 2.0), leisure time activities (lumateperone, 2.0; placebo, 2.2), and sexual drive, interest, and/or performance (lumateperone, 2.0; placebo, 1.9). By Day 43, lumateperone treatment significantly improved 8 of the 14 items in the Q-LES-Q-SF: mood (P = .0012); household activities (P = .0049); social relationships (P = .0075); family relationships (P = .0034); leisure time activities (P = .0020); ability to function in daily life (P = .0022); sexual drive, interest, and/or performance (P = .0468); overall sense of well-being (P = .0283). Overall life satisfaction also significantly improved with lumateperone treatment (P = .0016).

The largest improvements with lumateperone 42 mg compared with placebo (ES > + 0.3,) were seen in items representing the ability to function in daily life (+0.34), family relationships (+0.32), household activities (+0.31), leisure time activities (+0.34), mood (+0.35), and overall life satisfaction (+0.35; all LSMD, 0.3; all P < .01).

Conclusions: In patients with bipolar I or bipolar II disorder experiencing an MDE, treatment with lumateperone 42 mg compared with placebo significantly improved patient quality of life and functional impairment. These results support lumateperone 42 mg as treatment of MDEs associated with bipolar I or bipolar II disorder.

Keywords: Bipolar Depression, Lumateperone, Functional Disability

Disclosure: Intra-Cellular Therapies, Inc.: Employee, Stock/Equity (Self)

P320. Impaired Coping in Rats Exposed to Chronic Mild Stress: Modulatory Effect of Chronic Lurasidone Treatment

Marco Andrea Riva*, Ilaria Pisano, Veronica Begni, Francesca Marchisella, Kerstin Camile Creutzberg, Federico De Rosa, Mariusz Papp, Annamaria Cattaneo

University of Milan, Milan, Italy

Background: Exposure to stress represents a major risk factor for the onset of psychiatric disorders. Accordingly, exposure of adult rats to chronic stress represents a valuable experimental tool to characterize the mechanisms that may contribute to the vulnerability, or resilience, to stress exposure. One key trait in psychiatric patients is represented by disturbances in emotional control. While emotional control is a human feature, exposure to acute challenges in rodents can be used to investigate key pathways and systems that may be relevant in emotional control. Here, we used the chronic mild stress (CMS) paradigm to identify changes in the responsiveness to an acute stress and we investigated the potential impact of a chronic treatment with the antipsychotic drug lurasidone in ameliorating the functional changes produced by CMS exposure.

Methods: Adult male rats were initially exposed to CMS for 2-weeks and sucrose intake was measured as a proxy for anhedonia. Animals that showed reduced intake (vulnerable) were randomized to receive vehicle or the antipsychotic drug lurasidone (3.0 mg/kg, per os) for 5 more weeks while continuing CMS exposure. A sub-group of animals was also used to investigate the responsiveness to an acute challenge, as a proxy of emotional control, by exposing them to a 30 min-immobilization stress, whereas control rats were left undisturbed in their home cages. Blood and brain tissues were collected for the molecular analyses. Statistical significance was ascertained by two-way ANOVA followed by Tukey’s and Sidak’s multiple comparison test, when appropriate. Significance was set at p < 0.05

Results: CMS exposure caused a significant reduction in sucrose intake, which was normalized by lurasidone treatment (p < 0.001), with an effect that develops progressively during the treatment. CMS exposure produced significant changes in molecular systems associate with emotionality, including neuroplasticity-related genes, GABAergic function, and redox mechanisms, with a beneficial effect exerted by chronic lurasidone. Next, we investigated the modulation of brain-derived neurotrophic factor (BDNF), a trophic molecule linked to the pathophysiology of depression, as a proxy of functional plasticity in response to an acute challenge. We found that exposure of control animals to an acute stress up-regulates Bdnf expression in the prefrontal cortex, as a protective mechanism to cope with the challenging event. Such modulation is impaired in rats exposed to CMS, but it is restored by sub-chronic lurasidone administration. This data prompted us to map BDNF transcriptional changes specifically in parvalbumin (PV) and calcium calmodulin kinase II (CAMKII) positive neurons, the major inhibitory and excitatory neuronal populations of the PFC. For control animals, we localized acute stress-induced increase of BDNF transcripts in PV cells (p < 0.05), an effect not observed in CMS rats. However, we observed a significant increase of BDNF expression in pyramidal cells of CMS rats treated with lurasidone (p < 0.05), but not in PV cells.

Conclusions: In summary, we provide new insights on the mechanism of action of lurasidone in the context of stress-related dysfunction, suggesting that the antipsychotic drug may improve specific psychopathological domains. Moreover, our results suggest that pharmacological intervention produces adaptive changes leading to alterations of brain circuits that correct the functional activity and responsiveness of key brain regions involved in stress response and that may ultimately promote resilience.

Keywords: Chronic Unpredictable Mild Stress, Neuroplasticity, Stress Resilience, BDNF

Disclosure: Angelini, Otsuka, Lundbeck, Recordati: Honoraria (Self) Sunovion: Grant (Self)

Sumitomo Dainippon Pharma: Consultant, Grant (Self)

P321. Cerebellar Transcranial-Magnetic Stimulation as a Potential Treatment in Bipolar Disorder

Victoria Muller Ewald*, Laren Garrett, Nicholas Trapp, Krystal Parker

University of Iowa, Iowa City, Iowa, United States

Background: Bipolar Disorder (BD) symptoms include impairment in the coordination of cognitive processes and emotions. Recent work has implicated cerebellar (ceb) abnormalities in the pathophysiology of BD, including dysfunctional interactions between the ceb and the medial frontal cortex (MFC). As the ceb-MFC interactions are important for cognitive and mood regulation, the present work sought to boost ceb-PFC connectivity through cerebellar transcranial-magnetic stimulation (ceb-TMS). Additionally, ceb-TMS has recently been used to improve cognitive and mood symptoms in patients with schizophrenia. As schizophrenia and BD have phenomenological overlap, including the target symptoms of cognitive deficits and depressed mood, there is reason to be optimistic that patients with BD will benefit from the same treatment protocol.

Methods: In the present double blinded clinical trial, the safety and efficacy of using ceb-TMS in BD was examined. Both men and women suffering from BD (n = 30) were pseudorandomly divided into active and sham treatment groups with optional crossover at the end of the trial. Neuro-navigated TMS of the cerebellar vermis or sham treatment was provided 2x/day for 5 days (total of 10 treatments). A theta-burst stimulation protocol was utilized, consisting of 50 Hz triplets repeated at 5 Hz delivered for 2 s and followed by an 8 s pause. Neurobiological mechanisms underlying cognitive symptoms in BD were investigated via electroencephalography (EEG - Aim 1). Effects of TMS on cognitive symptoms were evaluated via clinical scales and cognitive tasks including the supra-second interval timing task (Aim 2).

Results: Contrary to our hypothesis, we found that participants who received active ceb-TMS showed reduced trial-wide low frequency activity (delta and theta bands) compared to those who received sham treatment. Reduction in low-frequency oscillations were specific to interval-timing task performance, as this effect was not observable during rest. Event-locked spectral analyses indicate that while participants who received sham treatment had an increase in cue-elicited low frequency power, this increase was prevented by the active ceb-TMS treatment. Despite oscillatory differences between sham and active groups, no significant differences in interval timing and cognitive/mood scales were detected.

Conclusions: The present work suggests that ceb-TMS is a safe and well-tolerated treatment for individuals with BD. EEG analyses indicate that ceb-TMS leads to a reduction in MFC low-frequency activity. However, effects on mood/cognition were not detected.

Keywords: TMS EEG, Cerebellum, Bipolar Disorder

Disclosure: Nothing to disclose.

P322. A Multi-Omics Approach to Understanding ATP Utilization Deficits in Major Depression

Sinead O’Donovan*, Xiaojun Wu, Jim Reigle, Rawan Alnafisah, Khaled Alganem, Alex Joyce, Robert McCullumsmith

University of Toledo, Toledo, Ohio, United States

Background: Bioenergetic dysregulation is an established facet of severe mental illnesses like major depression (MDD). ATP is the body’s primary energy carrier and is required to maintain most cellular processes. Dysregulation of ATP generation via glycolysis and mitochondrial respiration is implicated in MDD but much less is known about how ATP utilization is altered and its effect on downstream biological processes in disease.

Methods: To assess the expression and activity of the complement of proteins that utilize ATP (the ATPome) in the brain in MDD, we carried out bioinformatic and biochemical analysis. For preliminary biochemical analysis, ATP-binding enzymes were enriched in postmortem dorsolateral prefrontal cortex (DLPFC) from age, sex and PMI matched MDD and non-psychiatrically ill subjects (n = 3/group). Using a desthiobiotin-ATP probe, protein samples were enriched for ATP-binding enzymes and were analyzed by mass spectrometry (5600 TripleTOF, ABSciex). The activity of a subset of ATPome enzymes, serine/threonine kinases, were analyzed using the array-based Pamgene12 (Pamgene Int) in male and female dorsolateral prefrontal cortex (DLPFC) from age, sex and PMI matched MDD subjects and non-psychiatrically ill controls (pool n = 3-10 subjects/group). Z-score +/- 2 following permutation analysis by Kinase Random Sampling Analyzer (KRSA) indicates that a kinase was mapped to significantly altered peptides (log fold change +/-0.4) more or less frequently than expected by chance. For bioinformatic analysis, a targeted “ATPase” gene list was generated and filtered from Gene Ontology (GO) Annotation using “ATPase” and “Kinase” as search terms. Significant differentially expressed genes from this list were extracted from publicly available male and female postmortem MDD transcriptomic datasets. Pathway enrichment (GO, KEGG, Reactome) and pathway clustering by parent-child analysis were conducted.

Results: Biochemical enrichment of ATP-binding proteins resulted in the positive identification of ATPase enzymes, protein kinases and known ATPase-interacting proteins in enriched samples compared to negative (no probe) control for each subject. Approximately 200 ATPome proteins, including Na + /K + ATPase subunits, mitogen activated protein kinases (MAPK) and protein kinase C (PKC) were differentially expressed (FC expression > ±1.2) in the DLPFC in MDD compared to control. Analysis of serine/threonine kinase activity identified a significant increase (p < 0.05) in global signal intensity in MDD. Altered MAPK family activity was also identified by kinome analysis. MAPKs were predominantly found in female MDD subjects, conversely, a greater number of dark kinases were identified in male subjects. Commonly identified kinases include AKT and PKC, suggesting disease and sex-specific changes in expression and activity of protein kinases in the DLPFC in MDD. Bioinformatic analysis identified approximately 300 significantly differentially expressed “ATPase” genes (p < 0.05) in each MDD dataset. Clustering of GO pathways (FDR < 0.1; density index minimum 0.5) found significant enrichment of metabolic and signal transduction pathways in MDD. Stress-response pathway clusters were enriched in male subjects, suggesting sex-specific differences in ATP utilization pathways in MDD.

Conclusions: Bioinformatic and biochemical analysis of postmortem datasets and tissue confirm transcript, protein and activity-level perturbations of ATP utilization pathways in MDD. Preliminary proteomic analyses found significant ATPase and kinase enzyme expression changes in the DLPFC in MDD. These findings were complemented by kinome analysis, which found kinases with altered activity in male and female MDD subjects compared to controls. Pathway analysis integrating data from multiple MDD transcriptomic datasets highlighted both common and unique enriched biological pathways that are perturbed in males and females in MDD. Integrating omics and bioinformatic data provides insight into the mechanisms underlying ATP utilization deficits and its contribution to the pathophysiology of MDD.

Keywords: Proteomics, Major Depression Disorder, Bioenergetics, Kinomics

Disclosure: Nothing to disclose.

P323. Changes in Functional Connectivity Following Intermittent Theta Burst Stimulation (iTBS) are Proportional to the Electric-Field at the Cortex

Nicholas Balderston*, Romain Duprat, Marta Teferi, Yvette Sheline, Desmond Oathes

University of Pennsylvania, Philadelphia, Pennsylvania, United States

Background: Noninvasive neuromodulation is increasingly being applied to effectively treat mental illness. Transcranial magnetic stimulation (TMS) is currently approved by the FDA for the treatment of depression, obsessive compulsive disorder, and smoking cessation. The FDA-approved stimulation target for depression is the left dlPFC, and stimulation at this site is thought to alleviate symptoms by modulating functional connectivity with the stimulation site. Efforts to quantify the changes in connectivity following neuromodulatory TMS have largely focused on specific downstream targets of the stimulation site, potentially ignoring larger scale shifts in whole brain connectivity. Furthermore, this literature lacks a comprehensive model aimed at predicting large scale shifts in functional connectivity following neuromodulatory TMS. One simple approach to building such a model might be to assume that changes in connectivity are proportional to the energy delivered to the cortex, as operationalized by electric- (e)-field modelling. Accordingly, the purpose of this work is to predict changes in connectivity following TMS by modelling the electric field induced at the site of stimulation in a sample of depressed individuals recruited for a connectivity-based rTMS brief intervention.

Methods: Resting state functional magnetic resonance imaging (rs-fMRI) was collected from 16 depressed patients before and after they received 3 days of neuronavigated intermittent theta burst stimulation (iTBS) aimed at the left dlPFC delivered in 2 rounds of 1200 pulses each (2400 stimulations per session). The left dlPFC targets were chosen a priori based on connectivity between the left dlPFC and the subgenual anterior cingulate cortex (sgACC). NxN correlation matrices were constructed from the cleaned, parcellated (Gordon atlas) resting state timeseries. E-field models were parcellated using the Gordon atlas, vectorized, thresholded, and converted to NxN matrices reflecting the mean e-field norm for each pair of regions in the matrix. These e-field matrices were then used to predict pre-post changes in functional connectivity. For the primary analysis, e-field models were conducted at the site of stimulation and at a control region (contralateral motor cortex). For the secondary analysis, e-field models were conducted at 24 evenly spaced orientations for sites along a either an anterior-to-posterior (dlPFC) or inferior-to-superior (motor cortex) vector centered on the stimulation/control site from the primary analysis.

Results: For the primary analysis, we found that the e-field model based on the stimulation site predicted ~1.01% of the variability (v) in the pre-post functional connectivity changes, which was significantly greater than the variability predicted by the control site (v = 0.27%; t(15) = 2.4115; p = 0.029). For the secondary analysis, site x orientation heatmaps were created for both the stimulation and control site. For the heatmap centered on the stimulation site, there was a clear relationship between both site and orientation, and v-scores. As distance from the stimulation site increased, v-scores decreased. Similarly, as eccentricity from the optimal orientation increased, v-scores decreased. This pattern was not apparent in the heatmap centered on the control site. Permutation tests were conducted across site/orientation pairs in the heatmap with a cluster centered on the stimulation site/optimal orientation showing the strongest difference.

Conclusions: These results suggest that functional connectivity following iTBS changes systematically as a function of the energy reaching the cortex, and that this relationship can be described using e-field modelling. More importantly, this finding lays the groundwork for future studies that individualize TMS targeting based on how predicted functional connectivity changes might impact symptom expression. In a recent paper in NPP, we put forth a model aimed at doing just that. This model makes two assumptions. First, changes in network connectivity should be proportional to the TMS dose at the cortex, which is supported by the current work. Second, symptom change following TMS should be proportional to the association between network changes and symptoms. Although our NPP paper uses this model to make confirmatory predictions regarding left dlPFC stimulation and depression, prospective treatment using this targeting approach is necessary to support the second assumption of the model. However, if supported, this model could provide a domain-general whole-brain TMS targeting individualization approach applicable across mental disorders.

Keywords: TMS, Resting State Functional Connectivity, Electric Field Modeling

Disclosure: Nothing to disclose.

P324. Dissociable Effects of Cognitive Effort and Cognitive Flexibility on Anhedonia and Apathy

Alexander Herman*, Collin Meyer, Cathy Chen, Nicola Grissom, Dameon Harrell, Becket Ebitz, David Darrow

The University of Minnesota, Minneapolis, Minnesota, United States

Background: Anhedonia and apathy are transdiagnostic features of neuropsychiatric illness, predicting worse functional outcomes and diminished antidepressant response. Decreased willingness to apply cognitive effort may play a key role in these debilitating symptoms and interfere with current treatments such as cognitive-behavioral therapy. Cognitive flexibility, the ability to fluidly switch between mental states, goals or tasks, is also impaired in disorders with high levels of apathy and anhedonia, and decreased flexibility is associated with an increased risk for suicide. However, how cognitive flexibility relates to cognitive effort, and how these decision-making constructs jointly relate to critical depressive symptoms remains unknown. One possibility is that changes in flexibility are mediated partially or fully by changes in the subjective value of cognitive effort. Alternatively, cognitive flexibility and effort may contribute independently to the decreased motivation and reward sensitivity in anhedonia and apathy. Establishing a quantitative link between cognitive effort and flexibility and anhedonia and apathy would support the development of novel biomarkers and interventions for Major Depression and other neuropsychiatric disorders. Here, we make use of new developments in computational psychiatry to make quantitative, model-based measurements of cognitive effort and flexibility and connect them to core depressive symptoms.

Methods: 210 online participants recruited through Prolific (64 female, 146 male) completed a task measuring cognitive effort valuation, the Cognitive Effort Discounting Task (COGED) and a task measuring cognitive flexibility in an explore/exploit framework, a three-arm restless bandit task, along with inventories of neuropsychiatric symptoms including the PHQ-9, Snaith Hamilton Pleasure Scale (SHPS) and the Apathy Motivation Index (AMI). For the COGED data we computed the total area under the discounting curve (AUC) for each participant, a summary measure of the subjective value of cognitive effort. For the three-arm bandit behavior, we fit both a Hidden Markov Model (HMM) of exploration/exploitation and a novel foraging model of exploration/exploitation decisions to measure aspects of cognitive flexibility. While the HMM labels each trial as corresponding to either a state of exploration or exploitation, the foraging model decomposes behavior into a learning parameter, a decision threshold and an inverse temperature parameter that captures the amount of randomness in decisions, one measure of flexibility. We related the SHPS, AMI and PHQ-9 scores to these model-based task behavioral measures with generalized linear models.

Results: Participants consistently discounted increased levels of cognitive effort in the COGED task and performed better than chance on the bandit task. The median PHQ-9 score was 10, implying that approximately 50% of the sample displayed symptoms of moderate or severe depression. The cognitive effort AUC was weakly correlated with the bandit HMM probability of exploration (Spearman’s rho = 0.14, p = 0.055) but not with the inverse temperature parameter from the explore/exploit foraging model (rho = 0.05, p = 0.51). In separate linear regression, cognitive effort AUC predicted the SHPS score (beta = -0.21, p = 0.02) and the AMI social motivation sub-scale (beta = -0.1, p = 0.02); the inverse temperature parameter of our bandit foraging model predicted the SHPS score significantly (beta = -0.5, p = 0.014) and at a trend level the AMI emotional sensitivity (beta = -0.2, p = 0.1) and the PHQ9 (beta = -0.15, p = 0.06). The HMM probability of exploration and the other foraging parameters did not predict these symptom scores. In multiple linear regression, the cognitive effort AUC and inverse temperature both predicted SHPS score (p = 0.006 and 0.005, respectively) and the interaction was significant (p = 0.04); cognitive effort and inverse temperature also predicted the PHQ9 score (beta = -1, p = 0.02 and beta = 100.5, p = 0.002, respectively, interaction p = 0.01). Multiple regression results for AMI sub-scales were not significant. These results were confirmed with multiple ordinal logistical regression with quantile binned symptom scores.

Conclusions: We found that computational model-based measures of cognitive effort in the COGED task and cognitive flexibility in an exploration/exploitation bandit paradigm predict levels of anhedonia, apathy, and overall depressive symptom burden. Our results do not suggest a mediating role for cognitive flexibility in the relationship between effort and symptoms. Rather cognitive effort and flexibility appear to independently contribute specifically to anhedonia and interact more in explaining more severe symptoms and overall depression level. Measuring both cognitive effort and flexibility may thus be important to fully understanding individual variability in core symptoms of impaired motivation and reward sensitivity. These results support ongoing work in our group on the neural circuit correlates of effort and flexibility that may give rise to novel biomarkers and treatment targets for anhedonia and apathy.

Keywords: Anhedonia, Cognitive Flexibility, Effort Discounting, Computational Psychiatry, Depression

Disclosure: Nothing to disclose.

P325. Neural Response to Peer Feedback Moderates Effects of Social Stress on Depression Symptoms Among Adolescents

David Pagliaccio*, Rahil Kamath, Poornima Kumar, Diego Pizzagalli, Randy Auerbach

New York State Psychiatric Institute, Columbia University, New York, New York, United States

Background: Peer interactions become increasingly salient during adolescence, a time for increasing onset of internalizing disorders. Social mechanisms are a critical component of internalizing disorders risk – potentially blunted response to peer acceptance in depression and increased response to rejection in anxiety. Alterations in the neural underpinnings of social responsiveness are likely most salient in the context of acute social stress. In line with diathesis-stress models, we hypothesized that potentially deleterious effects of increased neural sensitivity to peer rejection would only manifest when individual are faced with peer rejection in daily life. The integration of neural and prospective stress measures to understand psychiatric risk has been lacking in the neuroscience literature.

Methods: Towards filling this gap, data were examined from N = 90 psychiatrically healthy adolescents (12-14 years old), either with (n = 26) or without (n = 64) a maternal history of depression. Teens completed the Chatroom Task during fMRI and provided self-report on stress experience (Adolescent Life Events Checklist) and depression symptoms (Mood and Feelings Questionnaire) up to nine times over the subsequent two years. Voxel-wise linear mixed effects models were fit to test our hypothesis that neural sensitivity to peer feedback would moderate stress effects on depression symptoms.

Results: While peer-related social stress was a strong predictor of depression symptoms longitudinally (β = 0.34, t(626) = 10.02, p < .001, ηp2 = 0.14), this interacted with brain response to peer acceptance vs. rejection in scanner in 70 regions (cluster corrected for multiple comparisons, voxel-wise p < .001). This included the bilateral anterior insula extending in the right posterior insula, bilateral caudate, dorsal anterior cingulate cortex, right putamen, and left amygdala. Parsing the interaction with activity in the left anterior insula (β = 0.12, t(623) = 5.366, p < .001, ηp2 = 0.13), we see a strong positive association between peer stress experience and depression symptoms among those with greater reject versus accept activity but this was not present in those with exhibiting greater accept versus reject activity.

Conclusions: These data highlight the combined influence of neural diatheses and social stress in understanding normal variability in subclinical depression symptoms during adolescence. This provides a critical framework for examining brain activity as a moderator (rather than an outcome variable) in whole-brain analyses to examine different models of the neuroscience of mental health. Currently, we find that differential neural sensitivity to peer feedback in key social processing regions is a risk/resilience factor to the experience of typically occurring social stress.

Keywords: fMRI, Social Rejection, Adolescent Depression, Psychosocial Stress

Disclosure: Nothing to disclose.

P326. Impact of Transcutaneous Vagus Nerve Stimulation on the Central Autonomic Network and Anxiety in Response to Stress in Major Depression

Ronald Garcia*, Justine Cohen, Arielle Stanford, Riccardo Barbieri, Harlyn Aizley, David Gitlin, Vitaly Napadow, Jill Goldstein

Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, United States

Background: Alterations of cardiac autonomic function in response to negative stressful stimuli have been implicated in the comorbidity of major depression (MDD) and cardiovascular disease (CVD). Further, there is often considerable concomitant anxiety symptomatology in MDD which contributes to greater affectation of cardiovagal regulation and increased cardiovascular risk. It has been proposed that alterations of brain regions involved in stress response and emotion regulation are responsible for the cardiovagal dysfunction observed in MDD, with women presenting greater affectation compared to men. Given the significant impact of the comorbidity between MDD and CVD, it is necessary to develop novel treatments at the neural-cardiac interface. Recently, transcutaneous auricular vagus nerve stimulation (taVNS) has emerged as a safe, non-invasive alternative to implanted VNS, with promising beneficial effects on regulation of depressive symptoms and cardiac autonomic function. Neuroimaging studies suggest that taVNS effects are mediated by modulation of the nucleus tractus solitarii (NTS) from which projections synapse with regions involved in cardiac autonomic regulation. Further, as NTS is highly influenced by respiration (receiving facilitatory inputs during exhalation), an optimized respiratory-gated approach (RAVANS) has been proposed by our team. The present study evaluated the effects of RAVANS on modulation of anxiety symptoms and brain circuitry involved in stress response and autonomic regulation in women with active recurrent MDD. MDD women were studied initially given they have twice the risk than men.

Methods: Twenty premenopausal women (age: 30.3 ± 4.7 years) with recurrent MDD in an active episode were included in an experimental cross-over study that included two functional MRI visits within one week. Subjects were randomized to receive 30 minutes of exhalatory-gated (e-RAVANS) or inhalatory-gated (i-RAVANS) stimulation during the first or second scanning session. Surface MR-compatible electrodes were placed in the left cymba concha of the auricle and stimulation consisted of monophasic rectangular pulses (300 usec pulse width, 30 Hz frequency, 0.8s duration) with current intensity set to achieve moderate (but not painful) sensation. Before and after the stimulation period, subjects underwent three runs (360s each) of a mild visual stress challenge task in the scanner comprising presentation of blocks of negative valence/high arousal, neutral valence/low arousal and fixation images adapted from the International Affective Picture System (IAPS). Whole-brain fMRI data were collected on a 3T scanner with a 32-channel head coil and a simultaneous multi-slice sequence (TR = 1250ms, TE = 33 ms, flip angle = 65º, FOV = 200 x 200 mm2, 75 axial slices, voxel size = 2 mm3). A piezoelectric transducer was used to collect heart rate data during the task and an adaptive point-process algorithm was applied to compute variations in instantaneous estimates of the high frequency component of heart rate variability (HF-HRV, 0.15 to 0.4 Hz). The State-Trait Anxiety Inventory (STAI) was collected at baseline and after the experimental sessions to evaluate changes in anxiety symptoms.

fMRI data were preprocessed using the CONN toolbox and included realignment, slice timing, motion correction, spatial smoothing and normalization and artifact detection. Comparisons of interest in the fMRI analysis (negative vs neutral, post-stimulation vs pre-stimulation) were tested using linear contrasts and results were submitted to a second level multiple regression analysis with changes in HF-HRV power as a covariate. We restricted the analysis to specific regions of interest (ROIs) from the central autonomic network (e.g., hypothalamus, amygdala, hippocampus, cingulate and prefrontal cortex) using a small volume correction approach. Changes in HF-HRV were included in regression analyses to investigate the link with changes in anxiety symptoms (STAI score difference: Post - Pre stimulation).

Results: e-RAVANS was associated with increased cardiovagal modulation in response to the visual stress task when compared to i-RAVANS (HF-HRV % change = 46.3 ± 33.8% vs 22.1 ± 30.7%, p = 0.03). Changes in HF power in response to e-RAVANS were related with increased activation of right dorsolateral prefrontal cortex (314 voxels, t = 4.98, p < 0.001) and anterior cingulate cortex (1672 voxels, t = 2.72, p < 0.01) and reduced activation of left amygdala (172 voxels, t = 3.60, p < 0.001). e-RAVANS also resulted in a significant reduction of anxiety symptoms compared to baseline (STAI = 47.8 ± 7.49 vs 55.2 ± 6.29, p < 0.01), which was significantly associated with increased cardiovagal modulation (HF-HRV change) (β = -1.93, t (16) =-2.73, p = 0.017, Adj R2 = 0.27).

Conclusions: Our results indicate that exhalatory-gated stimulation of the auricular vagus nerve effectively modulates brain circuitry involved the regulation of physiological response to stress in major depression. Further, our study revealed significant effects on anxiety levels in association with increased cardiovagal modulation. These results provide initial evidence supporting a novel neuromodulation approach with beneficial effects in acute relief of anxiety symptomatology and regulation of cardiovascular function that may be effective in the management of patients with comorbid MDD and CVD.

Keywords: Transcutaneous Auricular Vagus Nerve Stimulation (taVNS), Major Depressive Disorder, Central Autonomic Network, Functional MRI (fMRI), Heart Rate Variability

Disclosure: Nothing to disclose.

P327. Estradiol Mediates Stress-Susceptibility in the Male Brain

Polymnia Georgiou*, Liam E. Potter, Ta-Chung M. Mou, Panos Zanos, Michael S. Patton, Xiaoxian An, Katherine J. Pultorak, Sarah M. Clark, Vien Ngyuyen, Katalin Prokai-Tatrai, Istvan Merchenthaler, Laszlo Prokai, Margaret M. McCarthy, Brian Mathur, Todd Gould

University of Maryland School of Medicine, Baltimore, Maryland, United States

Background: Depression is the leading cause of disability worldwide afflicting ~16% of the population. Although, women are diagnosed with depression twice as often as men, there are approximately 109 million men worldwide suffering from the disorder. In addition, men suffering from depression are at higher risk to lose their life from suicide, one of the most common symptoms of depression, with suicide rates being four times higher in men than women. In susceptible populations, stress is a major risk factor for the development of mental disorders, including depression. While the role of estrogen receptors in the pathophysiology of depression and as treatment targets in females are widely elucidated, their role in males is not well understood.

Methods: We used a subthreshold social defeat stress model which consists of three cycles of two-min physical stress and fifteen-min of sensory stress, in combination with immunohistochemistry, neuronal tracing, RNAscope, in vitro electrophysiology, in vivo optogenetics, in vivo fiber photometry and hormonal manipulations to investigate the role of estradiol and its receptors in the development of social avoidance and anhedonia in male mice (n = 10-15). Statistical analysis was performed with ANOVAs followed by Holm-Sidak post-hoc analysis. If criteria for parametric analysis were not met, Kruskal-Wallis test was performed followed by two-stage linear step-up procedure of Benjamini, Krieger and Yekutieli.

Results: We found that absence of estrogen receptor-β (ERβ) is associated with stress susceptibility in male mice following exposure to a mild stressor. Activity of a subpopulation of ERβ-expressing neurons projecting to the nucleus accumbens (NAc) is reduced in male mice lacking gonadal hormones subjected to mild stress, while activation of this circuit reverses stress-induced maladaptive behaviors and induces stress resilience. Estradiol (E2), often considered a female specific hormone, is distributed in the male brain via aromatization of testosterone. We identified that absence of E2, but not testosterone per se, underlies susceptibility to develop maladaptive behaviors following exposure to mild stress in males. Using brain-selective delivery of E2 through administration of a prodrug, which offers a viable treatment option in males, we demonstrated that E2 prevents the development of depression-related behaviors following acute/mild stress in hypogonadal male mice.

Conclusions: Overall, our findings provide evidence for an estrogen-based mechanism underlying stress susceptibility and suggest a novel therapeutic strategy for treating depression in males.

Keywords: Depression, Estradiol, Estrogen Receptor, Circuits

Disclosure: Nothing to disclose.

P328. Application of a Bayesian Adaptive Randomization Design to Optimize Intravenous Ketamine Dosing for Late-Life Treatment-Resistant Depression

Nicholas Murphy*, Marijn Lijffijt, Sidra Iqbal, Charles Green, Tabish Iqbal, Lee Chang, Lorna Hirsch, Nithya Ramakrishnan, Dylan Fall, Alan Swann, Rayan Al Jurdi, Sanjay Mathew

Baylor College of Medicine, Houston, Texas, United States

Background: Evidence of the antidepressant efficacy of glutamate modulating drugs, especially the non-competitive N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine (and its S-enantiomer), has grown rapidly in recent years. Especially important is their rapid onset of action compared to other antidepressive agents, and their apparent effectiveness in patients not responding to established treatments. The antidepressant effects of a single intravenous (IV) dose of ketamine (0.5 mg/kg) typically begin within 24 hours of infusion, and persist for up to two weeks. The biological mechanisms of this prolonged impact are attributed to sustained patterns of increased excitation/inhibition (E/I) balance which outlast the short elimination half-life of ketamine. However, the clinical and biological effects of IV ketamine for late-life treatment-resistant depression (LL-TRD) have not been investigated, acting as a barrier to safe treatment of a growing clinical concern in geriatric medicine.

The aim of our investigation was to study the sustained clinical and neurophysiological effects of several doses of IV ketamine (KET) relative to midazolam (MID) in patients with LL-TRD. The simultaneous study of clinical and physiological data was designed to clarify the dose-related effects of ketamine on high-level changes in synaptic transmission, and how these changes might be related to the clinical outcomes at 7 days post-infusion.

Methods: Thirty-three veteran patients (55-72 years, mean age: 62.9 ± 5.86, 30.3% female), were enrolled in a randomized, double-blind, placebo-controlled design, and randomized to either a single infusion of IV ketamine (0.1, 0.25, or 0.5 mg/kg) or midazolam (0.03 mg/kg) condition. Randomization was achieved using Bayesian adaptive randomization (BAR) with an initial allocation ratio of 1:1:1:1. The allocation ratio was updated as patients completed the study to prioritize the comparison of the most clinically effective conditions. Patients completed evaluations on six visits to assess clinical effectiveness and durability of the infusion intervention (baseline and 1, 2, 3, 7, and 28 days post infusion).

We used Bayesian adaptations of generalized linear models to study the effects of time, drug condition, and time*drug interaction on clinical and physiological outcomes (EEG gamma oscillations). Our primary endpoint was the change in Montgomery-Åsberg Depression Rating Scale (MADRS) score between baseline and 7 days post-infusion. Durability was evaluated by estimating the probability of a clinical response to a single infusion at the 28 day visit for patients who demonstrated a clinical response to infusion at day 7. Gamma power was evaluated at 3 different time scales (-1 to +4 hours relative to infusion; 24 hours post-infusion; 24 hours to 7 days post-infusion). All analyses controlled for data values at the baseline time point. Kendall’s tau correlations were performed to draw inferences on the relationship between gamma power and change in MADRS.

Results: Infusions in all conditions were safe and well tolerated. The BAR stopping rules terminated randomization to 0.1 and 0.25 mg/kg ketamine conditions at N = 4 and N = 5, respectively, due to inferior clinical performance. The inferior conditions were explored in the analysis of our primary endpoint (MADRS change) but were omitted from the physiological analyses due to low power.

Sixteen patients (48.5%) achieved a clinical response at 7 days (KET 0.5 = 8, KET 0.25 = 2, MID = 6). Ketamine 0.5 mg/kg demonstrated a strong absolute probability (ap) of achieving a response at 7 days (ap = 0.7, 95% credible interval (95%-CrI) = 0.43 – 0.90), and was consistent with a higher response at 7 days than MID (Posterior Probability (pp) [KET 0.5 > MID] = 0.89). Probability of a clinical response was lower for ketamine 0.25 (ap = 0.42, 95%-CrI = 0.11 – 0.78) and 0.1 mg/kg (ap = 0.13, 95%-CrI = 0.01 – 0.53). Response durability at 28 days among responders at 7 days was greatest for KET 0.5 (N = 7, ap = 0.82, 95%-CrI = 0.52 – 0.97), and reduced proportionally with lower doses; KET 0.25 (N = 1, ap = 0.5, 95%-CrI = 0.09 – 0.90), MID (N = 2, ap = 0.37, 95%-CrI = 0.10 – 0.71).

Our data showed evidence of a significant time*condition interaction amounting to divergent effects of drug on gamma power over the course of metabolism (pp [KET 0.5 > MID] = 0.92). Gamma power rapidly increased during the infusion period for KET 0.5 and then gradually returned to baseline levels approximately 4 hours post-infusion (pp = 0.92), while the MID infusion was associated with a continuous upwards trend in gamma power over the duration of the recording (pp = 0.91). At 24 hours, there was low evidence of differences in gamma power between the conditions (pp [KET 0.5 > MID] = 0.37). Time* group changes in gamma power between 24 hours and 7 days post-infusion could not be determined by the model. Peak gamma power during infusion was associated with greater change in MADRS score at 7 days for KET 0.5 (τ = -0.5, p = .08), but not for MID (τ = 0.05, p = 0.84).

Conclusions: Our results suggest that IV ketamine at 0.5 mg/kg is clinically effective in LL-TRD. Our EEG findings provide preliminary evidence that the reactivity of gamma power might reflect susceptibility to enhanced clinical effects; precision medicine optimization of ketamine therapy will require further study.

Keywords: Ketamine, Treatment-Resistant Late Life Depression, Neuropsychiatry, Clinical Trial

Disclosure: Nothing to disclose.

P329. CCR2 Monocytes Repair Cerebrovascular Damage Caused by Chronic Social Defeat Stress in Mice

Miles Herkenham*, Joshua Samuels, Stacey Kigar, Chelsie Poffenberger, Michael Lehmann

National Institute of Mental Health/National Institutes of Health, Bethesda, Maryland, United States

Background: Mental disorders such as major depressive disorder (MDD) have a complex etiology. Genetic, biological, and environmental factors contribute to their manifestation. The great disease burden of MDD inspires attention to factors that might be studied to achieve basic understanding and potential therapeutic treatments. A well-studied contributing environmental factor is psychosocial stress. In animals, psychosocial stress can be studied using a paradigm called chronic social defeat (CSD). CSD in mice elicits depressive-like and anxiety-like behaviors, and it also produces elevated activity of microglia, oxidative stress responses in microglia and neurons, and scattered cerebral microbleeds with associated local blood-brain barrier (BBB) breakdown. Such physical events lie at the core of many brain disorders featuring cerebrovascular injury, such as stroke or traumatic brain injury. The innate peripheral immune system plays an important role in response to and resolution of such injuries. We therefore investigated the participation of innate immune cells—monocytes—during CSD and after cessation of CSD.

Methods: We measured activated CCR2hi monocyte trafficking to the vascular injury sites in Ccr2wt/rfp reporter mice both during two weeks of CSD (pairing of subject C57BL/6 mouse with a dominant CD-1 mouse in divided cage housing; barrier lifted for 5 min each day) and one week following CSD cessation (CSD recovery). Monocytes were tracked by immunohistochemistry/confocal microscopy and by flow cytometry of whole brain preparations. Fibrinogen (an inflammatory blood product) was both tracked and administered i.c.v. in some experiments. Clodronate liposomes were administered i.v. to deplete monocytes. Behavior was assayed in the urine scent marking (USM) task that reveals stress-induced asocial behavior.

Results: We replicated our earlier finding that CSD induces rare microhemorrhages distributed stochastically but somewhat more prevalently in cerebral cortex. The microbleeds were microscopically identified by the presence of i.v.-injected tracers, plasma immunoglobulin and fibrinogen, and erythrocytes present in perivascular spaces and adjacent parenchyma. Nevertheless, CSD did not recruit monocyte infiltration at these sites or anywhere else—the distribution and density of adhered CCR2-rfp+ monocytes was the same in home-cage control and CSD brains. However, after recovery from CSD, when fibrinogen is being cleared, many newly adhered CCR2 + cells were detected in perivascular spaces, and brain endothelial cells showed elevated gene expression of the CCR2 chemokine receptor ligands CCL7 and CCL12, but not CCL2. Flow cytometry showed that adhered CCR2 + cells were mostly the non-classical, anti-inflammatory Ly6Clo type, and confocal microscopy showed they phagocytosed fibrinogen. In Ccr2rfp/rfp mice lacking CCR2, fibrinogen was not cleared in CSD recovery. Fibrinogen infused intracerebroventricularly in unstressed mice induced CCR2 + cells to adhere to the vasculature in Ccr2wt/rfp but not Ccr2rfp/rfp mice. Depletion of monocytes with i.p.-injected clodronate liposomes during CSD recovery prevented fibrinogen clearance and blocked behavioral recovery in the USM task.

Conclusions: We hypothesize that peripheral CCR2 + monocytes play no role during chronic psychosocial stress because they lack key chemokine signals that might permit an inflammatory response to stress-induced microbleeds. However, during the stress recovery period, chemokine signaling permits anti-inflammatory monocytes to lodge in perivascular spaces, phagocytose blood products, and support vascular repair, promoting normalization of behavior post stress. These findings suggest that therapeutic administration of anti-inflammatory drugs during acute periods of stress recovery may hinder repair of vascular micro-damage and be counterproductive in the healing process.

Keywords: Neuroimmune, Brain Microvascular Endothelial Cells, Psychosocial Stress

Disclosure: Nothing to disclose.

P330. Ex Vivo Pharmacological Characterization of Selective M5 Acetylcholine Muscarinic Receptor Modulators on Dopamine Release in the Mouse Striatum

Vivien Zell*, Pascal Bonaventure, Grace Woodruff, Wayne Drevets, Bartosz Balana

Janssen Research and Development, San Diego, California, United States

Background: The type-5 muscarinic acetylcholine receptor (M5) is almost exclusively expressed in midbrain dopaminergic neurons, and thus is of particular interest for precise modulation of the mesolimbic pathway that is central to multiple neuropsychiatric diseases. Decreasing abnormally high dopamine transmission in the striatum has been a core approach in treating psychotic and manic symptoms of schizophrenia and bipolar disorders, while enhancing dopamine tone would be instrumental for the treatment of anhedonia, found in major depressive disorder. Indeed, M5 antagonists are promising candidates for treatment of drug misuse disorder based on their activity in preclinical models of drug abuse with cocaine, opioids, and alcohol. Although cloned over twenty years ago, and in contrast to the other four muscarinic receptor subtypes, functional pharmacological studies undertaken against a native tissue response exclusively mediated by M5 receptor activation are lacking. Here we characterize the capacity of M5-selective allosteric modulators to directly modulate dopamine release in the striatum, at the axon terminal level of the mesolimbic pathway in nucleus accumbens/caudate putamen slices.

Methods: The effects of ML375 (selective M5 negative allosteric modulator) and VU 0365114 (selective M5 positive allosteric modulator) on striatal dopamine release were evaluated using ex vivo fast-scan cyclic voltammetry (FSCV) in brain slices from wild-type and M5 knockout mouse. The significance of compound effect on dopamine release was tested using either a paired t-test or a linear mixed effects model for repeated measures.

Results: ML375 alone (10 µM) significantly decreased electrically-evoked dopamine release in the dorsal striatum of mouse brain slices (n = 7, p < 0.0001). Preliminary recordings show that in the presence of the acetylcholine nicotinic receptor blocker dihydro-β-erythroidine (DHβE, 1 µM), pre-incubation of the slice with ML375 (20min, 10 µM) completely abolished the increase in dopamine release induced by Oxotremorine-M (10 µM), a non-selective acetylcholine muscarinic receptor agonist (n = 5).

VU 0365114 alone (10 µM) significantly increased electrically-evoked dopamine release in the dorsal striatum of mouse brain slices (n = 6, p = 0.0016). Preliminary experiments show that in presence of DHβE (1 µM), pre-incubation of the slice with VU-0365114 (20min, 10 µM) augmented and prolonged the increase in dopamine release induced by oxotremorine-M (10 µM, n = 3).

Lastly, preliminary recordings in M5 knockout mice showed that oxotremorine-M did not significantly increase dopamine release in the dorsal striatum (n = 2).

Conclusions: In this study we established a functional pharmacological response exclusively mediated by M5 receptor activation in native brain tissue slices. Using FSCV in native tissue, selective M5 allosteric modulators, ML375 and VU0365114, both were capable of regulating dopamine signaling as measured by their impact on (1) electrically triggered dopamine release and (2) oxotremorine-M induced increase of dopamine release in the dorsal striatum. The effect of oxotremorine-M on dopamine release (at the axon terminal level) was absent in knockout mice assessing the specific effect on M5. Taken together these results highlight the important role of M5 in regulating dopamine release in the striatum. Muscarinic M5 receptors are an ideally located target capable of bidirectionally shaping dopamine signals in the mesolimbic pathways and thus, might be promising for the treatment of mood and other neuropsychiatric disorders.

Keywords: M5 Muscarinic Receptor, Dopamine, Allosteric Modulator, Striatum

Disclosure: Janssen Research and Development: Employee (Self)

P331. Distinct VIP Interneurons in the Cingulate Cortex Encode Anxiogenic and Social Stimuli

Connor Johnson, Lisa Kretsge, William Yen, Rhushikesh Phadke, Kelly Wingfield, Sarah Melzer, Jessica Jimenez, Balaji Sriram, Alexandra O’Connor, Ruichen Sky Liu, Thanh P. H. Nguyen, Eun Seon Cho, Tushare Jinadasa, Erelle Fuchs, Eli Spevack, Berta Escude Velasco, Frances Hausmann, Alberto Cruz-Martin*

Boston University, Boston, Massachusetts, United States

Background: A hallmark of higher-order cortical regions is their functional heterogeneity, but it is not well understood how these areas encode such diverse information. The anterior cingulate cortex (ACC), for example, is important in both emotional regulation and social cognition. Previous work shows activation of the ACC to anxiety-related and social stimuli, but it is unknown how subpopulations or microcircuits within the ACC simultaneously encode these distinct stimuli. One type of inhibitory interneuron, which is positive for vasoactive intestinal peptide (VIP), is known to alter the activity of many cells in local cortical microcircuits, but it is unknown whether the activity of VIP cells in the ACC (VIPACC) encodes anxiety-related or social information.

Methods: Experimental mice were male postnatal day 60-120 VIP-Cre mice (N = 6, Vip-IRES-cre, #010908). We used miniscopes to perform in vivo single-cell resolution calcium imaging of VIP interneurons in the ACC (VIPACC) to investigate their functional heterogeneity while mice performed tasks to assay anxiety-like behaviors, general sociability and social novelty. Behavior was analyzed using DeepLabCut, an open-source program that uses machine learning to track body parts in behavioral videos. Ca2+ imaging data were processed using CaImAn written in Python (https://www.python.org/). Responses of individual cells during different behavioral conditions were assessed within each behavioral trial using receiver operating characteristic (ROC) analysis. To determine whether VIPACC receive projections from other brain areas involved in anxiety and social behavior, we used rabies virus-mediated trans-synaptic mapping.

Results: Using in vivo calcium imaging and miniscopes in freely behaving mice to monitor VIPACC activity, we identified distinct, non-overlapping subpopulations of VIPACC that preferentially activated to either anxiogenic, anxiolytic, social, or non-social stimuli. We determined that stimulus-selective cells encode the animal’s behavioral states and VIP interneuron clusters may co-activate, improving this encoding. Finally, we used trans-synaptic tracing to show that VIPACC receive widespread inputs from regions implicated in emotional regulation and social cognition.

Conclusions: These findings demonstrate not only that the ACC is not homogeneous in its function, but also that there is marked functional heterogeneity even within disinhibitory interneuron populations. This work contributes to our understanding of how the cortex encodes information across diverse contexts and provides insight into the complexity of neural processes involved in anxiety and social behavior.

Keywords: VIP Neurons, Social Behavior, Anxiety Circuitry, Anterior Cingulate Cortex (ACC), Network Activity

Disclosure: Nothing to disclose.

P332. Subjective Response to Alcohol in Young Adults: Interactions With Bipolar Disorder and Associated Anterior-Paralimbic Structure and Recent Alcohol Use

Elizabeth Lippard*, Dylan Kirsch, Valeria Tretyak, Vanessa Le, Kim Fromme, Jorge Almeida, Stephen Strakowski

University of Texas at Austin, Austin, Texas, United States

Background: Alcohol use disorders are more prevalent in bipolar disorder than the general population. Mechanisms that contribute to elevated risk for alcohol use disorders in bipolar disorder are not known. Structural differences in anterior-paralimbic networks may predate and increase risk for problematic drinking in bipolar disorder. Moreover, recent evidence suggests medial orbitofrontal cortex (mOFC) structural differences may relate to variation in subjective response to alcohol in young adults with bipolar disorder. To extend these findings, we investigated subjective response to alcohol in young adults with bipolar disorder, compared to healthy young adults, and relations with mOFC structure and recent alcohol use.

Methods: To date, 22 young adults (13 with bipolar disorder type 1; mean age + standard deviation = 23 + 2 years, 50% women) have completed assessments of mood symptoms, recent alcohol use, and a structural MRI scan. Participants then completed placebo-controlled alcohol administration sessions in which they were dosed to a .08g% breath alcohol concentration and also completed a placebo drinking session (sessions counter-balanced). During beverage sessions, participants completed the Subjective Effects of Alcohol Scale (SEAS) at baseline (before beverage consumption) and at peak breath alcohol concentration of .08g%. The SEAS was filled out at a comparable time following beverage consumption during the placebo session. Changes in subjective response to alcohol were calculated for alcohol and placebo sessions. Group, session (alcohol, placebo), and group by session interactions were modeled, with beverage session as a repeated within subject variable, and SEAS subscale scores as the dependent variable. Age, sex, baseline heart rate, depression, and anxiety symptoms were covaried. Significance was defined as p < 0.05. Relations between subjective response to alcohol with mOFC structure and recent alcohol use in bipolar disorder were explored.

Results: Young adults with bipolar disorder, compared to healthy young adults, reported greater stimulation during the alcohol than placebo session (within bipolar disorder p = .004; group by condition interaction p = .03). Both groups reported an increase in sedation during alcohol administration compared with placebo (main effect of beverage session p < .0001). Greater stimulation reported during alcohol administration was associated with greater mOFC gray matter volume (pFWE(SVC) = 0.02) and lower frequency and quantity of recent alcohol use in bipolar disorder (p’s < .05).

Conclusions: Preliminary results from this ongoing study (registered at ClinicalTrials.Gov; NCT04063384) suggest greater stimulating effects of alcohol in young adults with bipolar disorder, compared to healthy young adults. Variation in development of anterior-paralimbic systems early in illness course may contribute to differences in subjective response to alcohol and greater alcohol use. Longitudinal study examining how neural progression relates to subjective response to alcohol and development of alcohol use disorders in bipolar disorder is the next step in this work.

Keywords: Bipolar Disorder, Alcohol Sensitivity, Young Adults, Medial Orbitofrontal Cortex, Alcohol Consumption

Disclosure: Nothing to disclose.

P333. Qualitative Analysis of Culture and Depression Treatment Among US Latinx Adults

Beatriz Manzor Mitrzyk*, Maria Santos, Ruth Bishop, Jose Valencia, Karen Farris

University of Michigan, Ann Arbor, Michigan, United States

Background: Despite consistent evidence of antidepressant effectiveness for depression management, early discontinuation is common in the US. Early discontinuation of antidepressants is associated with relapse, return of symptoms, and poor health outcomes. Latinx adults are at greater risk of early discontinuation than other groups; 54% of Latinx adults discontinue antidepressants within the first 30 days compared with 41% (P < 0.04) of non-Latinx white adults. Improving antidepressant use among Latinx adults could reduce mental health disparities. Previous qualitative studies have assessed Latinx adults’ perceptions, barriers, and knowledge of depression treatment. However, the themes identified by researchers such as stigma, familism, and discrimination could be difficult to extrapolate to clinical practice. The National Institute of Mental Health’s Strategic Plan requires that intervention studies identify targets or mechanisms that account for changes in clinical outcomes. The overall goal of this study is to identify potential targets or mechanisms for a future intervention to address early discontinuation of antidepressants among Latinx adults with depression.

Methods: We conducted guided focus groups of Latinx adults with depression recruited from 2 primary care clinics. Participants were asked open-ended questions about depression and depression treatment in the context of their Latinx culture such as: How did you decide you had depression? How did you seek and get treatment for depression? How does being Latino/a affect these decisions? and how does being Latino/a affect how someone will take medications for depression? Focus group meetings instead of phone interviews were selected because group dynamics often facilitate identification of cultural phenomenon. Meetings were conducted until we identified saturation among codes and themes. Participant responses were digitally recorded and transcribed verbatim in the original language (English or Spanish) using an online automated transcription service (trint.com) then edited by bilingual researchers for accuracy.

Qualitative data thematic text analysis was conducted using transcripts from focus group meetings. A team of researchers independently and iteratively analyzed and coded the data. We developed a preliminary codebook using a conceptual framework (adapted from Murray et al, 2004) to guide coding into major themes and subthemes. However, based on our meta-synthesis findings (completely separately), the codes and themes were revised to self-efficacy, resilience, and social determinants of health and their respective definitions. This study received an exempt determination by the University of Michigan Institutional Review Board (IRB; HUM00163233).

Results: We conducted 9 focus group meetings (median n = 3 per group) of 24 Latinx adults with depression. Four groups met from January to March 12, 2020, and five met from August to September 2020. Most groups (n = 6) met in person and 3 groups were conducted over Zoom. Focus group meetings were on average 1.5 hours long (range: 45 minutes to 2 hours). Most participants were female (83%; n = 20), of Mexican descent (58%; n = 15), born outside the US (46%; n = 11), preferred to speak Spanish (63%; n = 15), and were an average 41 years old. Key themes identified were:

  • Self-efficacy through verbal/social persuasion: encourage or discourage ambivalence towards depression treatment

    • “My mother-in-law was like, ‘Yeah, I’ve been on Wellbutrin and that’s [for] my anxiety and my depression. Maybe you should give it a try.’”

    • “If they think if you’re on treatment, it kind of makes you like the weirdo, the one that they kind of whisper about. So it’s kind of like, just don’t take it then, you don’t want to be talked about. You don’t want to be looked at as…crazy.”

  • Resilience through altruism: coping mechanism to overcome depression symptoms

    • “Especially being a mother, you’re supposed to be the caregiver, the provider. You don’t have time to be sad or angry. You gotta take care of the child. You gotta cook, you gotta clean. You got to be happy for everybody else.”

  • Mental health literacy: disagreement between facts and beliefs with a deference to negative beliefs over supportive facts about depression treatment

    • “If you rely so much on the medicine, it also becomes an addiction. Then it is like another disease that you have to try to cure.”

  • Antidepressant and treatment access: lack of understanding of the US health care system

    • “Well, for me it was also a little difficult because I did not know the language, but thanks to the fact that when my son was born, he was born with a little difficulty and a social worker took care of me…She gave me addresses, telephone numbers and well, thank God I have already started on [treatment].”

Conclusions: Findings were analyzed using the constructs of self-efficacy, resilience, mental health literacy, and treatment access. Unlike previous qualitative analyses of similar populations, all constructs are measurable, can be compared, and could be changed. The proposed constructs could be further explored as possible targets or mechanisms of antidepressant use in this population. We will use these findings to develop a culturally tailored intervention with the goal of reducing early discontinuation of antidepressants among Latinx adults with depression.

Keywords: Qualitative Research, Hispanic/Latinos, Depression, Antidepressants, Culture

Disclosure: Nothing to disclose.

P334. Impact of SER 109, an Investigational Microbiome Therapeutic on Health-Related Quality of Life in Patients With Recurrent Clostridioides Difficile Infection: Results From ECOSPOR III, a Placebo-Controlled Clinical Trial

Lisa Brown*, Hohmann Elizabeth, Feuerstadt Paul, Oneto Caterina, Charles Berenson, Lee Christine, Pham Sissi, Reese Pat Ray, Wu Henry, Wang Elaine, von Moltke Lisa, Garey Kevin

Seres Therapeutics, Brooklyn, New York, United States

Background: Clostridioides difficile infection (CDI) has a negative impact on health-related quality of life (HRQoL), particularly in patients with recurrent disease. In a randomized-controlled trial of 182 patients with recurrent disease (ECOSPOR-III, NCT03183128), SER-109, an investigational microbiome therapeutic, was demonstrated to be superior to placebo in reducing the risk of recurrent CDI (rCDI) (12.4% vs 39.8%, respectively; p < 0.001). The Cdiff32, a disease-specific HRQoL measure, was administered to assess the impact of SER-109 treatment on physical, social, and mental health domains, including anxiety as an exploratory outcome.

Methods: The Cdiff32 was administered in the ECOSPOR-III study at baseline, week 8, early termination, or recurrence of CDI. The Cdiff32 includes 32 questions with five levels of response measuring 3three domains (physical, social and mental). Twelve questions are specific to the mental health domain which includes mental (M), mental anxiety future (MAF), and mental anxiety current (MAC) subdomains. Domain items are scored from 0 (worst score) to 100 (best score) and aggregated by domain and globally. In the intent-to-treat population of ECOSPOR III, comparisons were made between SER-109 and placebo and by clinical outcome (ie, recurrence vs non-recurrence). The between treatment group comparison analysis controlled for age, sex, prior antibiotic use, and number of prior CDI episodes.

Results: Patient demographics and mean Cdiff32 scores were comparable between SER-109 and placebo at baseline, except the SER-109 arm had more females (67.4%). Patients achieved significant improvement in all Cdiff32 domains/subdomains at week 8 regardless of treatment group. When examining recurrence status within treatment arms, placebo patients with non-recurrence had significantly better scores on the mental health subdomains (M p < 0.001, MAF p < 0.001, and MAF p < 0.05) compared to those with recurrence. Notably, SER-109 patients with non-recurrence and recurrence showed improvement in all domains compared to baseline. Specifically, mental subdomains scores improved significantly from baseline in SER-109 subjects with recurrence (M p < 0.05, MAF P < 0.05, MAC P < 0.05). Therefore, patients in the SER-109 arm saw significant improvements in the mental health subdomains regardless of outcome whereas placebo only saw improvement in patients with non-recurrence.

Conclusions: In a Phase 3 trial in patients with rCDI, treatment with SER 109, an investigational microbiome therapeutic, led to significant improvement in Cdiff32 HRQoL scores. In contrast to placebo, SER-109 was associated with improved mental scores, regardless of clinical outcome. Future studies should evaluate whether SER-109 may provide mood and anxiety enhancing properties through modulation of the gut-brain axis.

Keywords: Microbiome, Microbiota-Gut-Brain Axis, Microbiota, Gut-Brain Axis, Fecal Microbiota Transplant

Disclosure: Tempus Labs, Seres Therapeutics: Employee (Self)

P335. Waist Circumference and its Association With Premenstrual Food Craving: The Premenstrual Hormonal and Affective State Evaluation (PHASE) Longitudinal Study

Ajna Hamidovic*

University of Illinois at Chicago, Chicago, Illinois, United States

Background: The premenstruum is marked by an increase in food craving in a significant number of reproductive age women, who are particularly vulnerable to weight gain. Functional magnetic resonance tomography studies show higher brain responses to food stimuli in the luteal vs. follicular phase, particularly in the corticolimbic areas involved in homeostasis and reward. The DSM-5 lists food craving as one of the symptoms (out of 11 total) for premenstrual dysphoric disorder (PMDD) and premenstrual syndrome (PMS) diagnoses. No study to date has established an association between either the PMS/PMDD diagnosis, or a particular premenstrual symptomatology, and central adiposity. The proposed study evaluated whether food craving experienced during the premenstrual period is associated with waist circumference. Based on the literature showing that women’s food craving increases premenstrually, and that there is an association between food craving and waist circumference in women in general, we hypothesized that there would be a positive association between premenstrual food craving and abdominal obesity.

Methods: Forty-six healthy women (mean BMI = 24.36), free of Axis I mental disorders, who were not taking medications, using drugs, drinking heavily, or smoking, prospectively provided daily ratings of food cravings across two-three menstrual cycles (122 cycles total). Their premenstrual rating of food craving was contrasted against food craving in the follicular phase to derive a corrected summary score (continuous variable) of the premenstrual food craving increase. Study groups were divided into normal (n = 26) and obese (n = 20) based on the 80 cm waist circumference cutoff, signifying an increase in a metabolic abnormality risk.

Results: The participants’ diagnoses were: PMS (n = 19), PMDD (n = 7), and healthy (n = 20). Waist circumference category was significantly associated with premenstrual food cravings (F(1,44) = 5.12, p = 0.028). Post hoc comparisons using the Tukey HSD test (95% family-wise confidence level) showed that the mean score for the premenstrual food craving effect size was 0.35 higher for the abdominally obese vs. normal study groups (95% CI: 0.039 to 0.67). The result was statistically significant even following an inclusion of BMI in the model.

Conclusions: In accordance with our hypothesis, the present study shows a positive association between premenstrual food craving and waist circumference. This association remained significant even after adjusting for BMI, which points to a particularly dangerous process of central fat accumulation. This is the first study to link food craving in the premenstruum with central adiposity. A potential relationship between premenstrual amino acid levels, reward processing, food craving, eating patterns and central adiposity should be investigated in future studies, with the overarching goal of integrating the premenstruum as a viable intervention target for this at-risk sex and age group.

Keywords: Premenstrual Dysphoric Disorder, Food Craving, Premenstrual Syndrome, Waist Circumference, Abdominal Obesity

Disclosure: Nothing to disclose.

P336. Stress, Genetics and Mood: Impact of COVID-19 on a College Freshman Sample

Cortney Turner*, Huzefa Khalil, Virgina Murphy-Weinberg, Megan Hagenauer, Linda Gates, Amy Tang, Lauren Weinberg, Robert Grysko, Leonor Floran, Thomas Dokas, Joan Zhao, Yu Fang, Srijan Sen, Juan Lopez, Stanley Watson Jr, Huda Akil

University of Michigan, Ann Arbor, Michigan, United States

Background: To study the interplay between genetic risk for depression and psychosocial stress, including the COVID-19 pandemic, in the emergence of symptoms of depression and/or anxiety in college freshmen. We distinguish between genetically- and non-genetically based types of resilience and their role during major life stressors.

Methods: University of Michigan freshmen (2015-2020) were characterized at baseline along clinical variables. They were genotyped and polygenic risk score for depression (MDD-PRS) was calculated. Their daily physical activity was captured, and they were sampled at multiple time points throughout the freshman year on clinical rating scales including GAD-7 and PHQ-9 for anxiety and depression, respectively. To assess the impact of the pandemic, the 2019-2020 cohort was analyzed separately.

Results: Across various years, 25%-57% of college freshmen developed significant symptoms of anxiety or depression. In the 2019-2020 cohort, measures of anxiety, depression and physical activity were all altered significantly after the onset of COVID-19. Physical activity, which differed between those who did vs. did not meet criteria for a mood disorder, was dramatically reduced by the pandemic.

High MDD-PRS conferred higher relative risk for depression/anxiety during a typical freshman year. Surprisingly, the pandemic had the clearest impact on the Low MDD-PRS group, which lost any evidence of genetic advantage. Conversely, psychological predictors of resiliency emerged as key factors in protecting the High MDD-PRS subjects who did not develop a mood disorder post-stress.

Conclusions: Although the pandemic increased mood disorders across the board, it eliminated the protection of genetic resilience. Psychological indices of resiliency were associated with protecting those with higher genetic risk.

Keywords: Stress, Depression, Genetics

Disclosure: Nothing to disclose.

P337. Holographic Stimulation of Distinct Amygdala Ensembles Responsive to Opposing Valences Bidirectionally Modulates Consummatory Behavior

Sean Piantadosi*, Charles Zhou, Tammy Nguyen, Garret Stuber, Michael Bruchas

University of Washington, Seattle, Washington, United States

Background: A central unanswered question in neuroscience is how can the heterogeneous and often opposing patterns of activity generated by genetically similar populations of neurons give rise to coordinated, complex behavior. Understanding whether these heterogeneous neural responses are necessary and sufficient to promote or suppress behavioral output is critical to determining how the brain produces behavior. Recent advances in both optogenetics and optical imaging approaches has made it possible to record endogenous stimulus-evoked neural activity patterns from individual neurons and holographically manipulate this naturally-defined activity pattern in select neurons. For the first time we harness this spatial light modulation (SLM) approach for reading and writing neural activity in a deep brain, subcortical structure, the basolateral amygdala (BLA). The BLA contains populations of excitatory principal neurons with diverse activity profiles that may encode the valence of salient stimuli. We posit that if these neurons encode the valence of a stimulus, select activation of discrete appetitive or aversive ensembles will bidirectionally modulate consummatory behavior.

Methods: Male (n = 8) and female (n = 3) C57BL/6 mice were injected with AAV8-Camk2a-ChRmine-mScarlett mixed 1:3 with AAVDJ-Camk2a-GCaMP6f into the BLA. A 7.3mm long, 0.6mm diameter GRIN lens was then lowered just above the viral injection. Mice were water restricted (1ml/day/mouse, 90% of original body weight) for one week prior to behavioral training. Mice were then habituated to head-fixation as well as trained to lick for 10% sucrose (in drinking water) solution for several days. Mice next underwent several two-photon (Bruker Ultima 2p+) imaging sessions during which they were exposed to random presentations of an appetitive (10% sucrose, 75% of trials) or aversive (2mM quinine, 25% of trials) tastant. Data were then processed (custom MATLAB and Python scripts) to identify BLA ensembles with preferential increases in activity to either the appetitive or aversive tastant. Subsequent sessions used holographic stimulation to directly play back this endogenous activity selectively to either appetitive (sucrose-activated) or aversive (quinine-activated) ensembles randomly on 50% of all trials. All experiments were carried out in accordance with the NIH Guide and approval of the University of Washington IACUC.

Results: Consummatory licking was significantly greater following delivery of appetitive 10% sucrose (75% of trials) compared to 2mM aversive quinine (25% of trials; p < 0.0001). In the BLA separable populations of sucrose-responsive (67/450) and quinine-responsive neurons (56/450) were identified (mean activity in response to sucrose > quinine, p < 0.05), as well as neurons that reliably responded to both tastants (88/450). Within individual mice, sucrose and quinine cells were spatially intermixed throughout the field of view. High resolution two-photon imaging allowed for reliable tracking of individual neurons across multiple days of recording, and appetitive and aversive ensembles were found to be highly stable across days, suggesting a consistent role in the processing of these stimuli. Having identified separable populations of appetitive and aversive principal neurons in the BLA with stable response properties, we conducted parameterization sessions in which holographic stimulation was matched to endogenous tastant-evoked activity. Stimulation reliably and specifically evoked activity only in targeted neurons and not nearby neurons. Tastant-evoked activity during trials with no stimulation was not significantly different from trials with stimulation (p > 0.05), suggesting that our stimulation intensity recapitulates natural physiological responses. During sessions in which quinine-activated ensembles were specifically targeted on 50% of trials (µ = 6.4 cells/mouse), a significant reduction in licking was observed on sucrose trials with stimulation compared to without stimulation (t(4) = 9.43,p = 0.0025). No change in licking was observed when stimulation occurred during quinine trials (p > 0.05). By contrast, when sucrose-activated ensembles were selectively stimulated on 50% of trials (µ = 7.75 cells/mouse), no change in licking behavior was observed when stimulation occurred during sucrose trials (p > 0.05). Critically, on trials in which quinine was delivered, stimulation of sucrose ensembles significantly increased licking compared to trials without sucrose ensemble stimulation (t(5) = 6.27,p = 0.003). In mice only expressing GCaMP6f (no ChRmine expression) targeting sucrose or quinine ensembles for stimulation had no effect on neuronal activity or on licking behavior (p > 0.05).

Conclusions: Gaining a mechanistic insight into how the brain encodes valence is necessary for understanding neuropsychiatric disorders where hedonic tone is often disrupted. The BLA has been identified as an important brain region for the regulation of emotion and integration of valence specific information across mammalian species and primates and is often implicated in a variety of psychiatric diseases. Here we demonstrate that separable populations of genetically similar BLA principal neurons encode the hedonic value of rewarding and aversive stimuli. This sets the stage for future investigation of how these stable opposing ensembles are affected during state-manipulations such as stress and drug exposure.

Keywords: Amygdala, Two-Photon, Optogenetics, Valence

Disclosure: Nothing to disclose.

P338. Cyclocreatine: A Bioenergetic Molecule Which Improves Depression-Like and Anxiety-Like Behaviors in an Animal Model of Treatment-Resistant Depression at Altitude

Shami Kanekar*, Robert Ettaro, Michael D. Hoffman, Hendrik J. Ombach, Jadeda Brown, Chandni Sheth, Kevin Jessing, Paul Sebahar, Perry Renshaw

University of Utah School of Medicine, Salt Lake City, Utah, United States

Background: Rates of major depressive disorder (MDD) and anxiety increase significantly with chronic hypoxia exposure at altitude (hypobaric hypoxia) or with chronic hypoxic disorders (COPD, asthma, cardiovascular disease or smoking). In a novel translational animal model, we find that depression-like and anxiety-like behaviors increase in rats housed at moderate altitude (4,500ft, 10,000ft) vs. at sea level, with sex-based differences. When housed at altitude, both sexes fail to respond to most selective serotonin reuptake inhibitors (SSRIs), the most widely prescribed of antidepressants. Living at altitude causes brain bioenergetic deficits in preclinical and clinical studies, and MDD is linked to brain hypometabolism. We therefore tested the potential of energetic compounds for the ability to correct altitude-related brain energy deficits and for antidepressant function at altitude. Creatine, an ergonomic compound widely used by athletes for decades, improved brain energetics in both sexes, but was only antidepressant in female rats at altitude. Creatine access to the brain is limited by the need of a specific transporter to cross the blood brain barrier, and the sex differences observed may be due to restricted access. Cyclocreatine (CyCR) is a synthetic lipophilic analog of creatine, which crosses the blood brain barrier without a transporter and can replace creatine in brain energetic pathways. CyCR exhibits higher brain bioavailability and greater stability vs. creatine. In this study, we tested CyCR as a therapeutic for depression-like and anxiety-like behaviors at altitude.

Methods: Rats housed at 4,500ft were given dietary CyCR in powdered food (3wks, 1%w/w), or un-supplemented food (controls). Rats were then tested for depressive symptoms in the forced swim and the sucrose preference tests. Another set of animals was assayed in a battery of tests including open field, marble burying, light/dark box and elevated T-maze. Brain regions linked to MDD (prefrontal cortex, striatum, hippocampus, brainstem) were harvested after behavioral testing, and assayed for CyCR and serotonin. Forced swim test data were analyzed by one-way ANOVA of CyCR, desipramine (positive control) and food controls, while other studies were analyzed by Student’s t-test for CyCR vs. food controls.

Results: A. Tissue Analyses: (1) CyCR: Dietary CyCR-treated animals exhibit serum CyCR levels of 64 ± 13mg/ml (females) or 120 ± 25mg/ml (males), while regional brain CyCR ranged from 515-765mg/g in females and 675-866mg/g in males (n = 7-15). Both serum and brain CyCR levels were negligible in food controls (0.03-1mg/ml, n = 8). (2) Serotonin: CyCR corrected the serotonin deficit in the female prefrontal cortex at altitude (Student’s t-Test, p = 0.02), but reduced striatal serotonin in males (p = 0.04, n = 11-18). B. Depression-like Behavior: (1) Forced Swim: CyCR showed antidepressant efficacy in both sexes, reducing immobility and increasing latency to immobility (LTI) by >20% vs. controls. In females, one-way ANOVA showed a significant effect of treatment on swimming (F2,88 = 5.3, p = 0.007), climbing (F2,93 = 8, p = 0.0005), immobility (F2,93 = 13.1, p < 0.0001) and LTI (F2,89 = 15.7, p < 0.0001). In males, one way ANOVA showed significant effects of treatment on climbing (F2,60 = 16, p < 0.0001), immobility (F2,63 = 10.7, p < 0.0001) and LTI (F2,63 = 4.97, p = 0.009), but not on swimming (F2,60 = 2.20, p = 0.12). CyCR significantly increased female swimming and male climbing, and increased LTI and reduced immobility in both sexes (p < 0.05). (2) Sucrose Preference: CyCR reduced anhedonia by increasing sucrose preference in both females (Student’s t-Test, p = 0.0009) and males (p = 0.02, n = 10-12). (3) Open Field: In both sexes, motor behavior did not change with CyCR treatment. C. Anxiety-like Behavior: CyCR also showed anxiolytic effects (n = 12). (1) Marble-burying: Rats given dietary CyCR exhibit lower anxiety-like behavior by burying fewer marbles vs. food controls (females: p = 0.047; males: p = 0.02). (2) Light/Dark Box: In females, CyCR significantly increased the latency to move from the bright side to dark side of box (p = 0.01), while a similar trend was seen in males (p = 0.08) (3) Elevated T-Maze: CyCR shows a trend to reduce general anxiety-like behavior and panic-like behavior in both sexes (p = 0.06).

Conclusions: Cyclocreatine is a novel bioenergetic compound which shows efficacy for depression-like and anxiety-like behaviors at altitude. Rates of MDD and anxiety increase with altitude of residence or chronic hypoxic disorders. Our preclinical studies indicate that chronic hypoxia exposure at altitude may alter brain physiology to worsen depression, anxiety and antidepressant-resistance. SSRIs are the primary antidepressants and long-term anxiolytics used in the US, but housing at altitude causes SSRIs to lose efficacy. This study shows that improving brain bioenergetics may provide a crucial therapeutic approach for treatment-resistant depression and anxiety. This is the first study to investigate the impact of CyCR as a treatment for depression and anxiety.

Keywords: Hypobaric Hypoxia, Altitude, Bioenergetics, Depression and Anxiety, Animal Models

Disclosure: Nothing to disclose.

P339. Intersection of Opioid and Nociceptive Networks in the Cingulate Cortex

Nora McCall*, Gregory Salimando, Benjamin Reiner, Richard Crist, Wade Berrettini, Gregory Corder

University of Pennsylvania, Philadelphia, Pennsylvania, United States

Background: Pain is an unpleasant emotional experience. Recent work from our lab and others have identified stable populations of neurons activated by acutely noxious stimuli in the amygdala and in the anterior cingulate cortex (ACC) key to the affective facet of pain. The action of opioids, the current standard of care for chronic pain, in the ACC plays a role in ameliorating the perception of the aversive quality of pain through mu opioid receptors (MOR). We hypothesize that MOR-expressing and nociception-active neurons in the ACC represents an overlapping population crucial to affective nociceptive behavior. We used single nucleus RNA sequencing (snRNAseq) to identify nociception-active cell types in the ACC that also express MOR. We also localized nociception-active ACC neurons and tested the influence of ACC MOR activity during nociception to gain further insight into the ACC MOR and nociception-active network.

Methods: ACC tissue for snRNAseq was collected in neuropathic pain or control mice (n = 5/condition, male). All mice experienced a noxious thermal stimuli prior to tissue collection to induce expression of immediate early genes (IEG). Next, single nuclei were isolated, cDNA libraries prepared, sequence, and aligned. Single nuclei clustering was performed in Seurat_v3. Well-characterized, a priori markers of cortical cell types were used to identify the subpopulations represented by each cluster (Slc17a7 for excitatory neurons, Gad1/2 for inhibitory interneurons). 14,220 individual nuclei (7,011 control, 7,209 neuropathic) were analyzed. MOR and nociception-active populations were identified by Oprm1 and 139 different IEGs, respectively.

To localize ACC nociception-active neurons, neurons activated by a noxious stimulus were labeled with tdtomato using a TRAP2 (Targeted Recombination in Active Populations):Ai9 line (n = 6, male and female); ACC nociception-active neurons were quantified with ImageJ.

In a preliminary study, ACC MOR neurons were chemogenetically inhibited during evoked behavioral responses to mechanical and noxious thermal stimuli (Oprm1-Cre line; n = 5-7; male and female).

Results: We identified 22 unique clusters from all major cell types (neurons and glia), including 8 glutamatergic neuron (Slc17a7) and 4 GABAergic interneuron (Gad1/2) clusters. We found Slc17a7 neuron clusters were the most transcriptionally active to the noxious stimuli, notably three clusters with single genetic identifiers: Otof, Figf, Npr3. The Figf cluster was also Oprm1 + , suggesting this cell type is well-positioned to influence nociceptive affective processes. Next, we determined the location of nociception-active neurons within the ACC. TRAP2:Ai9 histology revealed that nociception-active neurons are present throughout the ACC, with prominent labeling in layer 2/3 as well as 5. Finally, we assessed the role ACC MOR neuron activity on affective nociceptive behavior. Chemogenetic inhibition of ACC MOR neurons reduced responding to acute mechanical, but not noxious thermal, stimuli in control and neuropathic pain mice, suggesting ACC MOR activity can shift less valenced behavior.

Conclusions: We provide insight into the cell type and location of nociception-active and MOR neurons in the ACC, and insight into the behavioral effect of MOR ACC activity during nociception. Future studies will use intersectional approaches to manipulate MOR/nociception-active neurons during behavior, which we hypothesize mediates the affective analgesic effects of opioid therapies. Identifying specific networks underlying the therapeutic effects of opioids can aid the development of analgesics with improved selectivity.

Keywords: Mu-Opioid Receptors, Affective Components of Pain, Anterior Cingulate Cortex, Single-cell RNA Sequencing

Disclosure: Nothing to disclose.

P340. Sex Differences in Glucocorticoid Regulation of Dopamine Circuit Function

Ashley Holloway, Michael Schaid, Talia Lerner*

Feinberg School of Medicine, Northwestern University, Chicago, Chicago, Illinois, United States

Background: Stress is a significant risk factor for the development, and exacerbation, of numerous psychiatric disorders, including major depressive disorder (MDD). Corticosterone (cortisol in humans; CORT) is the primary ‘stress hormone’ in the body. In MDD, normal circadian rhythms of high and low CORT are flattened, leading to dysregulated and chronically elevated levels. Previous studies have found that static, chronically elevated levels of CORT induce anxiety-like behavior and impair reward-guided operant behaviors, but have only reported effects on male mice. We explicitly compared male and female mice and found that the effects occur exclusively in male mice. In the studies reported here, we explore the reasons for this sex difference in CORT-induced behavioral changes, which are potentially important for understanding sex differences in the prevalence of MDD and other stress-related disorders, as well as for designing appropriate therapeutics for both sexes.

Methods: We characterized CORT-induced behavioral changes using operant paradigms and open field tests. We then went on to determine how CORT differentially influences the function of the dopamine system in males and females using molecular biology and pharmacology to measure and manipulate dopamine transporters, and using the fluorescent dopamine sensor dLight1.3b to measure dopamine signals in the dorsomedial striatum and nucleus accumbens both in vivo during behaviors and in acute brain slices to further characterize how changes in the dopamine transporter influence dopamine release and reuptake.

Results: We found that chronic CORT administration selectively reduces operant reward-seeking in male mice. The effects in males were paralleled by decreases in dopamine transporter (DAT) function in the dorsomedial striatum (DMS) and nucleus accumbens core (NAcc). Using the DAT inhibitor GBR12909 (20 mg/kg), we found that chronic CORT treatment eliminated the increase in locomotion normally observed after DAT inhibition, but only in males. These results demonstrate a striking sex difference in how chronic CORT influences the dopamine system. We are currently working to further characterize the molecular mechanisms underlying this difference. We are also comparing the effects of chronic CORT exposure to the effects of a chronic mild unpredictable stress paradigm in males and females to better understand the different mechanisms by which stress may impair female behavior.

Conclusions: We conclude that chronically elevated CORT affects male and female mice differently, particularly with regard to DAT function. DAT function is crucial for dopamine homeostasis and transmission in vivo, thus its regulation by CORT may have profound effects on reward-guided behaviors in males and may be important for understanding the underlying causes of MDD and other stress-related disorders. However, it remains unclear how CORT affects DAT function in males, and why females are resilient to such an effect. Our future studies will address these questions and seek to translate our findings into better diagnoses and treatment options for MDD that take sex differences into account.

Keywords: Chronic Corticosterone, Corticosterone Response to Stress, Dopamine, Chronic Unpredictable Mild Stress, Sex Differences

Disclosure: Nothing to disclose.

P341. Abnormal Developmental Patterns of Neurocognition in Adolescents With Elevated Mood Symptoms

Roselinde Kaiser*, Elena Peterson, Amelia Moser, Chiara Neilson, Christina Hough, Benjamin Rosenberg, Christina Sandman, Christopher Schneck, David Miklowitz, Naomi Friedman

University of Colorado Boulder, Boulder, Colorado, United States

Background: Adolescence is critical period of neurocognitive development, including striking changes in executive functioning abilities and reward sensitivity. Adolescence is also a time of increased prevalence of mood pathology, and bipolar and unipolar symptoms have been linked to abnormalities in the same neurocognitive domains undergoing development during this period. However, it is unknown whether neurocognitive developmental patterns manifest differently for adolescents with elevated symptoms. This cross-sectional study replicated developmental patterns of neurocognitive functioning using a latent variable approach, and tested whether mood symptoms moderated developmental effects.

Methods: Participants were 606 adolescents (mean age = 19.38, SD = 2.44, 63% cisgender female) across two research sites recruited for high variance in current and past mood disorders. Participants completed three reward learning and three executive functioning tasks, and reported on age, pubertal stage, and (in n = 357, 55% with clinical mood disorders) severity of mania and anhedonic symptoms. Neurocognitive functioning was estimated using a methodologically superior latent variable approach. Structural equation models tested linear and curvilinear developmental (age, puberty) patterns of executive functioning and reward sensitivity. Manic symptom severity and anhedonic symptom severity were entered as moderators of developmental patterns. Sex was considered as a biological variable of interest.

Results: Structural equation modeling revealed a quadratic relationship between puberty and reward sensitivity that was moderated by mood symptoms: in early puberty, adolescents reporting higher mania exhibited heightened reward sensitivity whereas adolescents reporting higher (especially unipolar) anhedonia showed blunted reward sensitivity. Results also showed a linear relationship between age and executive functioning that was moderated by mania, in which adolescents reporting higher mania showed poorer executive functioning at older ages.

Conclusions: Findings indicate neurocognitive development may be altered in adolescents with mood pathology and suggest directions for longitudinal studies.

Keywords: Neurocognition, Adolescence, Mania, Anhedonia

Disclosure: Nothing to disclose.

P342. Adaptive Versus Maladaptive Forms of Regret After Chronic Social Stress

Brian Sweis*, Romain Durand-de Cuttoli, Freddyson J. Martínez-Rivera, Long Li, Angelica Minier-Toribio, Flurin Cathomas, Leanne Holt, Farzana Yasmin, Salma Elhassa, Jasmine Shaikh, Sanjana Ahmed, Scott Russo, Eric Nestler

Icahn School of Medicine at Mount Sinai, Minneapolis, Minnesota, United States

Background: Stress-related disorders such as depression are debilitating illnesses in which individuals struggle with severe emotional dysregulation. Regret describes the phenomenon in which an individual recognizes that an alternative action could have led to a better outcome. It is widely accepted that regret contributes to disease burden. Yet, little is known about the neurobiology of what might make this process maladaptive and what aspects of regret, if any, carry positive utility that is worth preserving in order to restore healthy emotional processing and adaptive coping. Animal models used for the study of depression and related disorders have made significant contributions to the field, including identifying key molecular mediators, such as CREB, which regulates the transcription of stress-sensitive genes that control responses to rewarding and stressful stimuli in a brain-region-specific manner. However, the role of CREB in decision-making is far less understood. Furthermore, animal models have been limited in their ability to capture the complexity of affective processes in decision making observed in human patients with stress-related disorders. To shed light on this translational gap, we combined the well-established chronic social defeat stress model in mice that effectively distinguishes between stress-susceptible and stress-resilient animals with molecular manipulations and novel approaches in neuroeconomics that have only recently demonstrated the ability to extract the behavioral and neurophysiological correlates of regret in rodents.

Methods: By characterizing mice exposed to chronic social defeat stress (CSDS) on a novel neuroeconomic decision-making paradigm termed “Restaurant Row” (RRow), we demonstrate fundamentally distinct forms of regret between stress-resilient (RES) versus stress-susceptible (SUS) phenotypes, and establish a region-specific role for CREB, a key transcription factor implicated in chronic stress action. We subjected C57BL/6J male mice to CSDS and identified SUS and RES mice based on a rapid social interaction screen. We then characterized SUS, RES, and non-stressed control (CON) mice longitudinally on RRow. Mice have a limited time period each day to forage for their sole source of food by navigating a maze with four uniquely flavored and contextualized feeding sites, or “restaurants.” Each restaurant has a separate offer zone (OZ) and wait zone (WZ). Upon entry into the OZ, a tone sounds whose pitch indicates how long of a delay mice will have to wait in a cued countdown should they choose to enter the WZ. A key feature of the RRow task is the ability to behaviorally segregate aspects of information processing that are directly linked to maximizing reward apart from other motivators. On this task, choice history can carry added weight capable of influencing subsequent decisions but only in certain economic situations defined by the subjective value of a specific sequence of offers and the combination of choices made. From this rich economic dataset across multiple dimensions of value, fundamentally distinct types of regret-inducing scenarios can be operationalized each with their respective counterfactual control decisions that could have been selected as an alternative and economically more advantageous option.

Results: We found that SUS mice were uniquely sensitive to regret type I: missed opportunities when rejecting high-value offers followed by encountering low-value offers. These scenarios capture risky decisions with poor outcomes to which neither RES nor CON mice were sensitive. Conversely, RES mice were more sensitive to regret type II: placing more weight on change-of-mind quit decisions in the WZ when correcting previous mistakes that followed accepting low-value offers in the OZ. SUS mice lost sensitivity to regret type II. Furthermore, RES mice were more sensitive to valuing past investments in the form of time already waited, or sunk costs, during these change-of-mind decisions. Overexpressing a dominant-negative form of CREB in the medial prefrontal cortex versus nucleus accumbens, a molecular manipulation known to promote SUS or RES respectively, differentially perturbed these distinct forms of regret.

Conclusions: These data reveal new insights into how adaptive versus maladaptive stress responses are related to distinct forms of counterfactual thinking. We found that one type of regret is absent as a loss-of-function effect in stress-susceptible animals and conversely enhanced as a gain-of-function effect in stress-resilient animals. Another type of regret is uniquely present as a gain-of-function effect in stress-susceptible animals only. The study provides a novel framework for understanding pathological versus healthy forms of regret that hinge on the framing of mistakes. This work can guide not only the development of new diagnostic tools or interventions for depression but can also steer psychotherapy toward unveiling distinct computations through decision narratives by directly inspiring new lines of psychodynamic questioning in patients in a way that may tap into circuit-computation specific processes.

Keywords: Depression, Neuroeconomics, Stress Resilience and Susceptibility, Prefrontal Cortex, Nucleus Accumbens

Disclosure: Nothing to disclose.

P343. Increased Expression of Excitatory Amino Acid Transporter EAAT3 in Forebrain Neurons Confers Resilience to Unpredictable Chronic Stress in Mice

Nicolás Ardiles, Francisca Henriquez-Belmar, María José Cossio, Andrés E. Chávez, Pablo Moya*

Instituto de Fisiología, Universidad de Valparaiso, Valparaiso, Chile

Background: The pathophysiology of depression is associated with dysregulation of the glutamate system and its clearance mechanisms in brain regions mediating cognitive-emotional behaviors. Chronic stress results in an increase in extracellular glutamate and dysregulation of the glutamatergic system in cortical and limbic brain areas both in patients with MDD and animal models of depression. However, the mechanisms underlying the abnormal glutamatergic transmission in depression are incompletely understood. The excitatory amino acid transporter 3 (EAAT3) - a member of the high-affinity glutamate transporters, which plays an essential role in transporting glutamate across plasma membranes in neurons, and in maintaining extracellular glutamate concentrations below neurotoxic levels, may have a pivotal role in the dysregulation of glutamatergic signaling associated to depression. This study seeks to evaluate the consequences of the unpredictable chronic mild stress (UCMS) model on the expression of glutamate transporters and receptors in the cortical-limbic brain areas in wild type (WT) mice and in EAAT3glo/CMKII mice, a novel transgenic mouse model with increased EAAT3 expression in forebrain neurons.

Methods: Animals: WT mice, control (EAAT3glo, no Cre) and CaMKIIα -driven EAAT3 overexpressing (EAAT3glo/CMKII) mice from both sexes were subjected to UCMS and compared to non-stressed mice for each genotype. 7-14 mice from both sexes were used per genotype, per condition.

UCMS: Mice were daily challenged to one or more stressors according to a semi-random schedule for 5 weeks. The stressors used were: restraint stress, modifying the light and dark cycle, wet bedding, substitution of sawdust with water, removal of sawdust, tilting the cage by 45°, repeated changes of bedding, replace home cage bedding by the bedding of a CF-1 mouse and stroboscope light.

Behavior: Mice were assessed for anxiety-like (open field test) and depressive-like behaviors (sucrose preference test, tail suspension test and social interaction test) in baseline (no stress) and UCMS conditions. Weight gain and coat status was also scored over the experimental timeline.

Molecular: Protein levels of AMPA and NMDA receptors subunits and glutamate transporters were analyzed by western blot.

Results: UCMS increased EAAT1 (t-test = -2.61, df = 4, p = 0.05), NMDA receptor GluN2A (t-test = -2.99, df = 8, p < 0.05) and GluN2B (t-test = -2.57, df = 10, p < 0.05) subunits, and AMPA receptors GluA1 (t-test = -5.21, df = 4, p < 0.01) subunits protein levels in the hippocampus in WT mice. WT mice and EAAT3glo (no Cre) control mice challenged to UCMS displayed increased anxiety like-behavior in the open field test and depressive-like behavior in all paradigms tested. As previously reported, in baseline conditions (no stress) EAAT3glo/CMKII mice displayed increased anxiety-like behavior. Remarkably, EAAT3glo/CMKII mice challenged to UCMS did not display any depressive-like behavior in the sucrose preference test, tails suspension test or social interaction test.

Conclusions: Hippocampal glutamatergic system alterations may underlie depressive-like behaviors. Our findings strongly suggest that forebrain EAAT3 gain-of-function may be linked to a resilient phenotype to chronic stress.

Keywords: Chronic Unpredictable Mild Stress, Glutamate Transporter (EAAT3), Depression, Glutamatergic Transmission

Disclosure: Nothing to disclose.

P344. Cortical Cell Cycle Abnormalities in Chronic Stress

Ana Mendes-Silva*, Thomas Prevot, Mounira Banasr, Etienne Sibille, Breno Diniz

Centre for Addiction and Mental Health, Toronto, Canada

Background: Stress is characterized as a state in which intrinsic or extrinsic stimuli evoke a dynamic and complex repertoire of biological, physiological, and behavioral adaptive responses of the organism. Stress can be either a triggering or aggravating factor for many pathological conditions, including cancer, coronary heart disease, major depressive disorder and neurodegenerative disorders. Several lines of evidence have indicated that the prefrontal cortex (PFC) is highly sensitive to stress, where stress induces volumetric, cytoarchitectural, and morphological changes. Consequences of chronic exposure to stress in the PFC include learning and memory impairments, and behavioral changes.

Little is known about chronic stress-induced changes in the cell cycle regulators in the brain, especially in the PFC. The p16 and p21 cyclin-dependent kinase inhibitors are involved in cell cycle pathways associated with the cellular stress response. In order to provide a better understanding of the impact of variable durations of CRS on the cell cycle regulation in PFC, we evaluated mRNA and protein levels of both p16 and p21 in mice. We also investigated potential links between p16 and p21 expression changes and anxiety- and depressive-like behaviors using correlational analysis.

Methods: Independent groups of C57BL/6J mice (6 groups, 8 mice/group, 50% female) were exposed to chronic restraint stress (CRS) from 3 to 35 days, and were assessed on behavioral tests measuring anxiety and anhedonia. In addition, PFC mRNA and protein levels of p16 and p21 were quantified using qPCR and Western Blot, respectively, at each time point. Correlation analyses were used to investigate the impact of chronic stress on the mRNA and protein expression of p16 and p21, and anxiety- and depression-like behaviors.

Results: Analysis of variance showed that p16 mRNA expression was significantly different across the stress groups (p = 0.006). When sex was added as a co-factor, there was no main effect of sex (p = 0.213) and the difference in mRNA expression of p16 across groups remained statistically significant (p = 0.006). Pairwise comparison showed that p16 mRNA expression was significantly reduced on days 3 (p = 0.031), 21 (p = 0.007), and 35 (p = 0.029) compared to the control group. p21 mRNA expression was significantly different among groups (p = 0.024). When sex was added as a co-factor, we found no main effect of sex on gene expression (p = 0.803), and the difference in the mRNA expression of p21 between groups remained statistically significant (p = 0.027). Pairwise analysis showed that p21 mRNA expression was significantly reduced only on day 28 (p = 0.037) compared to the control group.

p16 protein expression was significantly different among groups (p = 0.009). After including sex as a co-factor, there was no difference in the protein expression of p16 between groups (p = 0.129). We also found no main effect of sex on p16 expression (p = 0.899). Pairwise analysis showed that p16 protein expression was significantly increased on day 14 (p = 0.025) compared to the control group. We found a marginally significant difference on p21 protein expression among groups (p = 0.056). When sex was added as a co-factor, there was no difference in the protein expression of p21 between groups was found (p = 0.352), but we found a significant main effect of sex on p21 protein expression (p = 0.017). Pairwise contrast analysis showed that p21 protein expression was significantly increased on days 3 (p = 0.016), 14 (p = 0.005), 21 (p = 0.005), 28 (p = 0.045), and 35 (p = 0.028) compared to the control group.

Correlation analyses were performed to determine the potential relationship between p16 and p21 expression levels and behavioral outcomes. p16 mRNA expression was significantly negatively correlated with residual avoidance in the shelter zone (r = -.318, p = 0.034), positively with weight gain (r = .337, p = 0.024), and negatively with sucrose consumption (r = .355, p = 0.018). p21 mRNA levels showed a significant correlation with worsened coat state (r = -.400; p = 0.006). Splitting the samples by sex, there were no significant correlations between p16/p21 mRNA levels and behavior outcomes. p16 protein expression was significantly negatively correlated with worsened coat state (r = -.378, p = 0.011). p21 protein expression was also significantly correlated with reduced sucrose consumption (r = -.342, p = 0.036). Splitting by sex, correlations analysis revealed a positive correlation between p21 protein expression and residual avoidance in shelter zone (r = .547, p = 0.012) and reduced sucrose consumption (r = -.609, p = 0.004) in males, while the females showed no significant correlation with behavioral outcomes. Finally, we did not find a significant correlation between mRNA and protein expression levels of p16 (r = -.046, p = 0.768) and p21 (r = -.184, p = 0.262)

Conclusions: Our present study extends the existing literature providing evidence that postmitotic cells have a complex stress response that involves senescence markers. We confirmed that mice subjected to CRS showed dysregulation of cell cycle response systems, suggesting an abnormal response of the cellular defense system to stress linked to depressive-like behavior. In summary, these findings provide strong justification for future studies to investigate which brain region and cells display abnormal p16 and p21 mRNA and protein expression.

Keywords: Chronic Stress, Prefrontal Cortex, Kinase Inhibitor, Stress and Anxiety Behavior

Disclosure: Nothing to disclose.

P345. Maternal High-Fat Diet Causes Male Offspring-Specific Serotonin Deficiency

Alexis Ceasrine*, Benjamin Devlin, Jessica Bolton, Carolyn Huynh, Young Chan Jo, Bailey Patrick, Kamryn Washington, Susan Murphy, Leigh Ann Simmons, Staci Bilbo

Duke University, Durham, North Carolina, United States

Background: Over 50% of women in the United States are overweight when they become pregnant. Maternal high-fat diet (mHFD) creates an environment of chronic inflammation and is associated with detrimental outcomes for offspring, including increased susceptibility to psychiatric disorders. Despite these observations, many studies are correlative and do not propose a mechanism through which mHFD contributes to offspring psychiatric disorder development. The placenta is a critical interface between maternal environment and the developing fetal brain, and as such is poised to translate maternal insults into offspring neural outcomes. Further, the placenta is the primary source of fetal forebrain serotonin, and decreased serotonin signaling is correlated with increased vulnerability to stress in rodents. Serotonin levels are decreased in the context of inflammation; thus, we hypothesize mHFD-induced inflammation reduces prenatal serotonin levels, altering the development of the central serotonin system and causing anxiety-/depressive-like behaviors in mice.

Methods: We used a mouse model of maternal high-fat diet (mHFD) to determine placenta and brain macrophage density, placenta Tlr4 expression, and serotonin-dependent behavioral outcomes in male and female offspring (n > = 3 dams per diet per experiment; 2-way ANOVAs). We also assessed placental and brain serotonin levels in both mouse mHFD offspring and human fetal tissue in which triglyceride levels from maternal placenta were used as a proxy for maternal fat distribution (39 matched maternal decidua, fetal brain, and fetal placenta sets; linear regression analyses).

Results: Maternal high-fat diet increases macrophage density and toll-like receptor 4 (Tlr4) expression in male and female placenta, and Iba1 and CD68 immunoreactivity, gross measures of microglia activation state, in male and female fetal brain tissue (p < 0.05; main effect of diet 2-way ANOVA). Female mHFD offspring display diminished social behavior, and preliminary results suggests that abrogation of Tlr4-dependent signaling in macrophages improves behavioral outcomes in females. Male mHFD offspring display normal social behavior, but show increased depressive-like behavior, which is associated with decreased serotonin (5-HT). Maternal dietary tryptophan enrichment restores mHFD-induced serotonin deficiency in male offspring and rescues male behavioral deficits. Finally, in a set of 39 matched human fetal brain and placenta tissues, we observed that maternal triglyceride accumulation significantly negatively correlated with fetal brain serotonin levels in male fetuses only (r = -0.4909, p < 0.05 for males, r = 0.2286, p = 0.3062 for females).

Conclusions: Maternal high-fat diet and resulting high maternal weight negatively impact the development of the serotonin system specifically in male offspring, which may contribute to sex-biased psychiatric disorder susceptibility.

Keywords: Immunity and Neurodevelopment by Sex, Mood Disorders, Serotonin

Disclosure: Nothing to disclose.

P346. Ventral Hippocampal Projections to the Orbitofrontal Cortex Regulate Reversal Learning and Stress Resilience

Maryam Hasantash*, Ryan Shores, Christoph Anacker

Columbia University, New York, New York, United States

Background: Cognitive flexibility is impaired in many stress-induced psychiatric disorders, and higher levels of cognitive flexibility can promote stress resilience, possibly by enabling flexible adjustment of coping strategies. Which neural circuits regulate cognitive flexibility, and how these circuits are implicated in stress resilience, is largely unknown. An important aspect of cognitive flexibility is reversal learning, which is the ability to adjust behavior when previously learned action-outcome associations change. At the neural circuit level, studies have implicated the hippocampus and orbitofrontal cortex (OFC) in reversal learning. Our own previous work has highlighted the ventral part of the hippocampus as a crucial mediator of stress resilience. How the ventral hippocampus and OFC interact to facilitate reversal learning, stress coping, and resilience has never been investigated.

Methods: We bilaterally injected retrograde Cre virus (AAVrg.hSyn.HI.eGFP-Cre.WPRE.SV40) in OFC (mOFC), and Cre-dependent inhibitory hM4Di DREADD virus (AAV9.hSyn.DIO.hM4Di.mCherry; experimental mice) or mCherry virus (AAV9.hSyn.DIO.mCherry; control mice) in vCA1. To test vCA1-mOFC inhibition effects on reversal learning, male mice (n = 10 control, n = 10 inhibition) were food restricted to 85% body weight, trained to dig in two baited bowls, and learned that the rewarded bowl was marked with cinnamon scent and the unbaited bowl with Garlic. On the reversal day, the reward location was switched to Garlic scent and all mice were injected with CNO (5mg/kg, i.p.) 30min before the first trial. Mice were considered to have learned the association after 8 correct out of 10 consecutive trials. The number of trials to criterion was compared between groups using unpaired student’s t-test. For stress experiments, male mice (n = 6 control, n = 6 inhibition) were exposed to sub-chronic social defeat by aggressive male CD1 retired breeders for 5 min each day over a 5-day period. Distance travelled was recorded on each day of defeat as a measure of active escape/coping behavior and compared by 2-Way repeated measures ANOVA. Mice were tested in a social interaction (SI) test 24 hr after the defeat. The ratio of time spent with a novel mouse over time spent with an empty cup was analyzed using EthovisionXT (Noldus) and compared using unpaired student’s t-test. Overall mobility was tested in a 10 min open field test, and corticosterone (CORT) levels were measured in plasma using EIA assay (Arbor Assays) 30 min after exposure to acute stress. Both tests were analyzed by unpaired t-test. All data are mean±s.e.m.

Results: Chronic inhibition of vCA1-OFC projections impaired reversal learning in the Digging Task (Control: 21.2 ± 3.8 trials to criterion; Inhibition: 31.1 ± 4.48 trials to criterion; n = 10; unpaired student’s t-test: p = 0.0014). Projection inhibition reduced distance travelled during social defeat (Control: Day 1: 487 ± 16.5 cm; Day 2: 361 ± 13.2 cm; Day 3: 274 ± 14 cm; Day 4: 357 ± 15 cm; Day 5: 246 ± 10.9 cm; Inhibition: Day 1: 199 ± 6.4 cm; Day 2: 102 ± 9.2 cm; Day 3: 63 ± 8 cm; Day 4: 75.4 ± 5.9 cm; Day 5: 95.4 ± 6.3 cm; n = 6; Two-Way repeated measures ANOVA shows main effect of Inhibition: p = 0.0002. No effect of Day: p = 0.1014; no interaction effect: p = 0.8454).

without affecting distance travelled in an open field arena (Control: 2533 ± 304.1 cm; Inhibition: 2282 ± 156.4 cm; n = 6; unpaired student’s t-test: p = 0.48), indicating less active escape behavior (i.e., a more passive stress coping strategy) during defeat without effects on overall mobility. Mice with vCA1-OFC inhibition during defeat showed lower SI ratios than control mice (Control: 1.2 ± 0.1; Inhibition: 0.69 ± 0.07; n = 6; unpaired t-test: p = 0.007) and higher CORT levels in response to an acute defeat (Control: 268.9 ± 59.4ng/ml; Inhibition: 486.7 ± 43.5ng/ml; n = 6, unpaired t-test: p = 0.014), indicating higher levels of stress-induced social avoidance and stress reactivity.

Conclusions: Our results show that vCA1-OFC projections are important for reversal learning and for employing an active stress coping strategy during social defeat, which is important for stress resilience. Targeting vCA1-OFC projections may thus promote stress resilience and rescue cognitive flexibility deficits in psychiatric disorders.

Keywords: Cognitive Flexibility, Neural Circuits, Stress Resilience

Disclosure: Nothing to disclose.

P347. Sex Differences in Neural Representation of Threat in Ventral Hippocampal and Prefrontal Cortical Projections to Nucleus Accumbens

Jessie Muir*, Eshaan S. Iyer, Rosemary Bagot

McGill University, Montreal, Canada

Background: Learning about and responding to emotionally significant events is dysregulated in many neuropsychiatric disorders including depression and anxiety disorders. The nucleus accumbens (NAc) plays a role in neural encoding and behavioral responding to emotionally significant stimuli. To guide behavior, the NAc integrates dopaminergic input from the ventral tegmental area with information from several glutamatergic inputs, including the ventral hippocampus (vHIP) and prefrontal cortex (PFC). Previous work from our lab suggests that neural activity in the vHIP-NAc is increased by chronic variable stress and may also encode individual differences in vulnerability to future stress in both male and female mice. To understand more about how neural activity in this pathway, and another glutamatergic input, the PFC-NAc, is shaped by aversive experiences we examined neural activity during encoding of aversive stimuli (foot-shock) or threat predicting cues in male and female mice.

Methods: All experiments were conducted in accordance with guidelines of McGill University’s Comparative Medicine and Animal Resources Center and approved by the McGill Animal Care Committee. Using frame-projected independent fiber photometry (FIP) and GCaMP7f to image in vivo calcium activity across multiple brain regions in male (n = 8) and female mice (n = 9), we recorded NAc-projecting neurons in the PFC and vHIP during a Pavlovian fear conditioning paradigm in which mice encounter both threat cues (CS+) predicting shock (0.5sec, 0.5mA) and neutral cues (CS-) with no outcome.

Results: Neural activity in both the vHIP-NAc and PFC-NAc encodes aversive foot-shock and differentiates a threat-predictive cue from a neutral cue, with pathway-specific temporal patterns and sex differences. Both pathways show large elevations in activity in response to foot-shock (PFC: M: n = 8, p = 0.005; F: n = 9, p = 0.0004; vHIP: M; n = 8, p = 0.008 F; n = 9, p = 0.004), and in the PFC-NAc, this neural response was greater in females than males (p = 0.02). We observe that, upon robust behavioral discrimination of threat-predicting and neutral cues, neural activity in vHIP-NAc is significantly elevated at cue onset to the CS + compared to the CS- in males (p = 0.01) but not females (p > 0.92). In the PFC-NAc, neural activity during the CS + was suppressed immediately prior to cue termination and shock delivery in females (p = 0.04) but not males (p = 0.1).

Conclusions: Our findings show that both the vHIP and PFC relay information about threat prediction to the NAc that may underlie appropriate fear responding, with significant sex differences. The elevated PFC-NAc response to foot-shock in females may be relevant to understanding mechanisms of increased vulnerability to chronic stress. Similarly, differences in neural activity during aversive cues in both PFC-NAc and vHIP-NAc suggest pathway-specific sex differences in neural encoding of threat that may relate to sex differences in responding to threat.

Keywords: Fear Conditioning, Stress Resilience and Susceptibility, Fiber Photometry

Disclosure: Nothing to disclose.

P348. Behavioral and Molecular Aftermath of a Single Psychedelic Drug Exposure in Mice

Mario de la Fuente Revenga*, Javier Gonzalez-Maeso

Virginia Commonwealth University, School of Medicine, Richmond, Virginia, United States

Background: Psychedelics, traditionally best-known for their mind-altering properties, are emerging as a potential new paradigm in the treatment of certain mood disorders. The most distinct characteristic of their potential therapeutic effect is its lingering nature, as improvements persist long after the acute action dissipates. We aimed to characterize behavioral manifestations and molecular correlates in mice 24h after exposure to a psychedelic drug (DOI).

Methods: Utilizing wild-type and 5-HT2A receptor knockout (KO) male mice we characterized the involvement of 5-HT2AR in learned helplessness and the development of synaptic plasticity. Inclusion of females is part of our current work in progress. Mice (C57BL/6) were administered with the potent serotonin 5-HT2A/2CR-selective agonist DOI (2 mg/kg). We also included a battery of molecular (frontal cortex 5-HT2AR binding) and behavioral assays (expression of head-twitch responses, or HTR) to determine the development of tolerance to the drug action in wild-type and Beta-arrestin 2 (Barr2)-KO animals.

Experiments involving behavior assays and molecular readouts employed 5-15 male mice per treatment and genotype group depending on the paradigm employed. Statistical significance of experiments involving two groups (i.e., drug vs. vehicle) was assessed by Student’s t test. Experiments that involved measures during a time-course (i.e., drug vs vehicle during different epochs) and/or involved different variables (i.e. treatment and genotype) were assessed by two-way ANOVA followed by Sidak’s multiple comparison test. The level of significance was set at p = 0.05.

Results: We observed increases in activity in the forced swimming test and faster development of contextual fear extinction upon cessation of the noxious stimulus in wildtype, but not in 5-HT2A-KO mice, 24h after exposure to DOI. Concurrently, we observed increases synaptic plasticity and downregulation of 5-HT2AR density in the frontal lobe. Mice also developed tolerance to the acute effects of the drug on HTR upon re-exposure to DOI. This effect was blocked by a 5-HT2AR antagonist (M100907), but it was unaffected by the absence of Barr2.

Conclusions: Adaptive responses and synaptic plasticity phenomena observed in mice following administration of DOI 24h prior involved 5-HT2AR on its action. We also observed that such exposure resulted in a decrease of frontal cortex 5-HT2AR density and manifestation of DOI-induced HTR at that same timepoint through a Barr2-independent mechanism. Our results further support the idea that the effect of psychedelics is not limited to their acute pharmacological interactions; conversely a lingering complex behavioral and molecular landscape unfolds. How these different domains are intertwined will be crucial to understand the substrates of psychedelics potential as therapeutics.

Keywords: Psychedelics, Adaptive Behavior, Tolerance

Disclosure: Consultancy fees: Consultant (Self)

Share holder: Stock / Equity (Self)

P349. Multi-Omic Characterizations of Suicide Attempts in Adults With Major Depressive Disorder Reveals Associations of Circadian Genes and Plasma Metabolites

Caroline Grant*, Angelina Wilton, Rima Kaddurah-Daouk, Michelle Skime, Joanna Biernacka, Taryn Mayes, Thomas Carmody, Liewei Wang, William Bobo, Richard Weinshilboum, Madhukar Trivedi, Arjun Athreya, Paul Croarkin

Mayo Clinic, Rochester, Minnesota, United States

Background: Suicidality is a global public health challenge. In the absence of predictive biomarkers, identifying individuals at risk of attempting suicide is challenging, as standard clinical and risk assessments are inherently subjective. Twin and adoption studies estimate that the heritability of suicide attempts may be as high as 50%. Predictive biomarkers that identify individuals at risk for suicide attempts would assist with enhanced risk assessments and the development of targeted therapeutics.

Methods: We developed a search strategy to identify single nucleotide variants (SNVs) associated with suicide attempts, with the following criteria: ((SNV) OR (SNVs) OR (SNP) OR (SNPs) OR (single nucleotide variant) OR (single nucleotide variants) OR (single nucleotide polymorphisms) OR (single nucleotide polymorphisms)) AND ((suicide attempt) OR (suicide attempts)). Significant (by study definition) SNVs were extracted. Additionally, the GWAS Catalog was searched for suicide-attempt traits, and SNVs of suggestive significance (p < 10-5) were extracted. Genotypes for these SNVs were obtained from 245 individuals with Major Depressive Disorder (MDD) from the Pharmacogenomics Research Network Antidepressant Medication Study (PGRN-AMPS) and 111 individuals with MDD from the Combining Medications to Enhance Depression Outcomes (CO-MED) study. Patients (n = 46) from PGRN-AMPS and CO-MED with prior suicide attempts were identified. Chi-Square tests assessed genetic associations with suicide attempt history. Additionally, 153 metabolites (glycerophospholipids, carnitines, sphingomyelins, amino acids, and biogenic amines) were assayed at baseline (before initiation of antidepressant therapies) with the Biocrates p180 platform in PGRN-AMPS and CO-MED individuals. To better understand the relationships between SNVs associated with suicide attempts and metabolomic profiles of suicide attempters, metabolomic and genomic integration analysis was conducted. The resulting networks, comprising correlated SNVs and metabolites, were compared in individuals with and without a history of suicide attempts to identify potential biomarkers of interest.

Results: The literature search produced 227 studies, 113 of which met our study inclusion criteria, yielding 187 unique SNVs. The GWAS Catalog search produced 31 studies, 28 of which met inclusion criteria, yielding an additional 176 unique SNVs. There were significant differences among 9 SNVs in PGRN-AMPS and CO-MED individuals with and without a history of suicide attempt according to chi-square tests (p < 0.05). rs1982350, an intronic SNV in ARNTL (Aryl Hydrocarbon Receptor Nuclear Translocator Like, which encodes the BMAL1 protein), was the most significant (p = 8.1E-05). Metabolomic and genomic integration demonstrated that rs1982350 along with rs3805148 (an intronic SNV in CLOCK) were associated with several phosphatidylcholines, amino acids, and kynurenine in suicide non-attempters (p < 0.05; r > 0.1). However, these SNV and metabolite associations were absent from the network of suicide attempters. The ARNTL (BMAL1) and CLOCK SNVs and their associated metabolites most significantly differentiate the networks of suicide attempters and non-attempters. This statistical result suggests a potential functional relationship between the CLOCK and ARNTL (BMAL1) SNVs, their associated metabolites, and suicidality. In the literature, BMAL1 and CLOCK heterodimerize to initiate transcription of circadian rhythm genes. Additionally, circadian rhythm dysfunction (e.g., disrupted sleep patterns) has been associated with suicide attempts.

Conclusions: The relationship of circulating phosphatidylcholines, amino acids, and kynurenine with BMAL1:CLOCK regulated circadian processes may be disturbed in suicide attempters. This aligns with disrupted circadian processes (e.g., sleep) in suicide attempters. This relationship should be further investigated to better understand the joint influence of circadian signaling and phosphatidylcholine, amino acid, and kynurenine variation on risk for suicide attempts. An improved understanding may ultimately yield clinically actionable laboratory tests to identify individuals at an increased risk of attempting suicide and advance drug discovery.

Keywords: Multi-omics, Suicide Attempt, Genomics, Metabolomics

Disclosure: Nothing to disclose.

P350. Methodological Challenges in Psychedelic Drug Trials: Efficacy and Safety of Psilocybin in Treatment-Resistant Major Depression (EPIsoDE) – Rationale, Study Design and Current Status

Lea Mertens*, Michael Koslowski, Felix Betzler, Ricarda Evens, Maria Gilles, Andrea Jungaberle, Henrik Jungaberle, Tomislav Majić, Andreas Ströhle, Max Wolff, Stefan Wellek, Gerhard Gründer

Central Institute of Mental Health, University of Heidelberg, Mannheim, Germany

Background: Psychedelic drugs represent one of the most promising treatment approaches in contemporary psychiatry (Gründer, 2021; Gründer and Jungaberle, 2021). Specifically, psilocybin, a partial serotonin (5-HT) 2A receptor agonist, has shown promising safety and efficacy results in the treatment of major depression and other psychiatric disorders (e.g. reviewed in Rucker et al., 2018; Mertens and Preller, 2021). While results from modern pilot studies on psilocybin in the treatment of major depression and other psychiatric disorders are promising, most of those trials lack randomization, double-blinding, and a sufficient sample size. The use of double-blinding and an appropriate placebo is particularly difficult in psychedelic trials, facing ethical issues as well as the problem of “expectation bias” and the risk of nocebo effects in patients in the comparator groups (Gründer and Mertens, in press). Accordingly, there is an immense need for additional, larger, well-designed randomized-controlled studies.

Methods: Objectives: The phase 2 EPIsoDE-Trial (NCT04670081) aims to investigate the efficacy and safety of a high psilocybin dose (25 mg, p.o.) administered in a psychotherapeutic context in treatment-resistant major depression in a randomized-controlled, bi-centric, parallel-group, double-blind design. We expect significant and stable treatment responses after a high (25 mg) dose of psilocybin in comparison to placebo (100 mg nicotinamide) and a low/supposedly inactive control dose (5 mg psilocybin), while provoking only mild and transient adverse events (AE). As a secondary objective the effect of a second high dose six weeks after the first dose will be assessed. Exploratory objectives are aimed at identifying potential neurobiological and psychological therapeutic mechanisms of psilocybin treatment.

Methods: 144 patients (25 – 65 years of age) diagnosed with treatment-resistant major depression of moderate to severe degree will be enrolled in the study, all of which will receive two dosing sessions six weeks apart. Treatment-resistance is defined as no improvement in depression despite two adequate courses of antidepressant treatment. After informed consent and potentially down-titration of their antidepressant medication, patients will be randomized to one of four treatment arms: 1) receiving placebo (100 mg nicotinamide) first, 25 mg psilocybin second; 2) receiving the presumably sub-effective psilocybin dose (5 mg) first, the high dose (25 mg) second; 3a) receiving 25 mg psilocybin first, 5 mg psilocybin second; 3b) receiving the high psilocybin dose (25 mg) at both sessions. Dosing sessions will be accompanied by multiple psychotherapeutic preparation and integration sessions. The second dose takes place after assessment of the primary endpoint; the primary endpoint is treatment response, defined as a minimum of 50% reduction in symptoms as measured with the Hamilton Rating Scale for Depression (HAM-D), six weeks after the first dose.

Results: -

Conclusions: The trial is currently being conducted at the Central Institute of Mental Health (sponsor) in Mannheim as well as the Charité Universitätsmedizin Berlin, Campus Charité Mitte. The trial design, including the randomization, double blinding and comparator conditions, will allow valid conclusions on the efficacy and safety of psilocybin treatment in major depression.

The trial is funded by the German Federal Ministry of Education and Research (BMBF 01EN2006A and 01EN2006B); it has been approved by the Federal Institute for Drugs and Medical Devices (BfArM) and the responsible Ethics Committees.

References:

Gründer G. (2021). Psychedelics: A New Treatment Paradigm in Psychiatry?. Pharmacopsychiatry, 54(4), 149–150. https://doi.org/10.1055/a-1520-5020

Gründer, G., and Jungaberle, H. (2021). The Potential Role of Psychedelic Drugs in Mental Health Care of the Future. Pharmacopsychiatry, 54(4), 191–199. https://doi.org/10.1055/a-1486-7386

Gründer, G., and Mertens, L. J. (in press). Psilocybin for depression. The New England journal of medicine.

Mertens, L. J., and Preller, K. H. (2021). Classical Psychedelics as Therapeutics in Psychiatry - Current Clinical Evidence and Potential Therapeutic Mechanisms in Substance Use and Mood Disorders. Pharmacopsychiatry, 54(4), 176–190. https://doi.org/10.1055/a-1341-1907

Rucker, J., Iliff, J., and Nutt, D. J. (2018). Psychiatry and the psychedelic drugs. Past, present and future. Neuropharmacology, 142, 200–218. https://doi.org/10.1016/j.neuropharm.2017.12.040

Keywords: Psilocybin, Major Depression Disorder, Randomized-Controlled Trial, Treatment-Resistance

Disclosure: Nothing to disclose.

P351. Enduring Downregulation of Critical Transcriptional and Translational Cellular Stress Signaling Gene Networks in Postpartum Depression

Sarah Rudzinskas*, Allison Goff, Maria Mazzu, Crystal Schiller, Samantha Meltzer-Brody, David Rubinow, Peter Schmidt, David Goldman

National Institute of Mental Health, NIH, Rockville, Maryland, United States

Background: Postpartum depression (PPD) affects 15% of women and results in numerous negative health outcomes for both mother and child. Given the burden of this illness, there is immense value in defining molecular markers that could confer PPD risk, symptomology, and heritability in women. During pregnancy, circulating levels of estradiol and progesterone (E2 + P) rise >10-fold above those normally present across the menstrual cycle, then fall rapidly at birth. Clinically, the administration and withdrawal of these supraphysiologic levels of E2 + P induces symptoms of depression in asymptomatic, ovarian-suppressed women with a history of PPD, but not in control women participating in an identical hormone manipulation protocol (Bloch et al., 2000). Furthermore, previous studies suggest both genetic and epigenetic differences in women at risk for PPD.

Methods: To better understand the cellular role of E2 + P in precipitating mood symptoms in PPD, we derived lymphoblastoid cell lines (LCLs) from women with past PPD (n = 9) and matched asymptomatic control women (n = 11) with no history of PPD or Axis 1 psychiatric illness. All LCLs were cultured in three treatment conditions to mimic the hormonal states that occur during pregnancy and parturition: no added E2 + P (Baseline); supraphysiologic E2 + P (Addback); and supraphysiologic E2 + P followed by E2 + P removal (Withdrawal). LCLs were then subjected to whole-transcriptome RNA sequencing. Quality control, unsupervised clustering, analysis of differential gene expression (edgeR), and weighted gene correlation network analysis (WGCNA) were all performed in R.

Results: EdgeR detected differentially expressed genes (DEGs) between PPD and control LCLs in all three treatments but saw the most profound statistical difference (>30 FDR corrected p < 0.05 DEGs) with E2 + P Addback. There was significant overlap in DEGs across experimental conditions, suggesting a pronounced role of past PPD on gene expression. The most statistically significant of these DEGs were IMPACT and WWTR1, highly evolutionarily conserved genes that were decreased in PPD. IMPACT (F(1,54) = 45.96, p < 0.0001) is a translational regulator that maintains homeostasis during circumstances of cellular stress. WWTR1, aka TAZ (F(1,54) = 52.06, p < 0.0001), is a transcriptional co-activator that mediates cell proliferation and apoptosis in the stress shunting ‘Hippo’ signaling pathway. IMPACT and WWTR1 were significantly correlated (F(1,18) = 18.86, p = 0.0004), and their protein expression was significantly decreased in PPD (p < 0.01). Further analysis of E2 + P Addback and Withdrawal specific DEGs revealed that GATA3 (nominal p < 3.56x10-5) and MYC (nominal p < 2.91x10-4), hormone-mediated transcription factors that can alter IMPACT and WWTR1 expression, were significantly increased in PPD. Although downstream WWTR1-mediated genes are not well expressed in LCLs, the downstream targets of IMPACT, like eiF2α, showed significant changes in phosphorylation in a E2 + P-dependent fashion. Finally, WGCNA revealed eight diagnosis-significant modules, most of which were significantly linked to the GATA3 and MYC-associated E2F transcriptional networks.

Conclusions: These findings implicate both E2 + P-independent and -dependent differential cellular responses in PPD. The magnitude of overlap in DEGs between treatment groups suggests that past PPD is strongly reflected in significantly altered gene expression. The enduring dysregulation of evolutionarily conserved transcription (WWTR1, E2F, GATA3, MYC) and translation (IMPACT) networks may suggest women with PPD could have an impaired ability to maintain typical cellular homeostasis with the stress of pregnancy. The differential effects of hormone Addback and Withdrawal in PPD were present, but more mechanistically nuanced. For instance, although eiF2a was not a DEG in any treatment condition, eiF2α-Ser51 phosphorylation, of which IMPACT is a primary mediator, was significantly changed in PPD compared to control LCLs only after E2 + P withdrawal. Furthermore, the finding that the most extreme gene expression differences were during E2 + P Addback (and not during Withdrawal) potentially provides molecular support for recent work suggesting PPD may begin before parturition. Future studies will investigate the E2 + P-sensitive mechanisms underlying the roles of IMPACT, WWTR1, and E2F gene networks in other models for PPD, to better understand how an altered ability to regulate transcriptional and translational cellular response may influence mood or PPD risk.

Keywords: Postpartum Depression, Estradiol, Progesterone, Ovarian Hormones, RNA-seq

Disclosure: Nothing to disclose.

P352. Interactions Between Peripheral Myeloid Cells and the Brain in Stress-Impaired Social Behaviors

Flurin Cathomas*, Hsiao-Yun Lin, Kenny Chan, Long Li, Romain Durand-de Cuttoli, Lyonna Parise, Antonio Aubry, Aarthi Ramakrishnan, Samer Muhareb, Sara Costi, Jun Wang, Fiona Desland, Miriam Merad, Li Shen, James Murrough, Scott Russo

Icahn School of Medicine at Mount Sinai, New York, New York, United States

Background: Chronic psychosocial stress, an important risk factor for major depressive disorder (MDD), induces profound changes in the immune system associated with behavioral alterations relevant to MDD. However, the mechanisms linking peripheral immune system activation and neuronal dysfunction in the Nucleus accumbens (NAc) and as a consequence, deficits in social reward processing, are still poorly understood.

Methods: In a murine model of chronic social defeat stress (CSDS), we applied mass cytometry, bulk and single-cell RNA-sequencing to characterize immune cells in circulation and the central nervous system. Using pharmacological and genetic strategies, we investigated the causal effects of the identified murine targets on stress-induced behavioral and electrophysiological changes. Lastly, using a translational approach, we validated the murine findings in patients with MDD and non-depressed healthy controls (HC).

Results: In circulation, CSDS led to a dysregulation of several leukocyte subpopulation frequencies of both the myeloid and lymphoid lineage. In brain, however, we observed an increased accumulation of Ly6chigh monocytes in brain-border regions specifically in susceptible mice. Single-cell RNA-sequencing of brain infiltrating monocytes identified increased expression of the endopeptidase matrix metalloproteinase 8 (Mmp8) in stress-susceptible versus resilient or control mice. Plasma levels of MMP8 correlated positively with social avoidance. Combination of intraperitoneal administration of recombinant MMPs and a subthreshold social defeat was sufficient to induce social avoidance and reduced social reward. Bone marrow chimeric mice that lack Mmp8 only in peripheral immune cells also showed decreased CSDS-induced social avoidance compared to wildtype chimeras. These behavioral changes went along with blunted stress-induced increased spontaneous excitatory postsynaptic currents (sEPSCs) and neuronal excitability in the NAc. Finally, we showed that plasma levels of MMP8 were increased in patients with MDD compared to HC.

Conclusions: Our findings provide mechanistic evidence that neuro-immune interactions are relevant to the etio-pathophysiology of stress-induced social behavior deficits. Targeting specific inflammatory molecules such as matrix metalloproteinases could constitute interesting novel therapeutic targets for stress-related neuropsychiatric disorders.

Keywords: Depression, Inflammation, Nucleus Accumbens, Immune System, Social Defeat Stress

Disclosure: Nothing to disclose.

P353. Psilocybin Therapy Increases Cognitive and Neural Flexibility in Patients With Major Depressive Disorder

Manoj Doss*, Michal Považan, Monica Rosenberg, Nathan Sepeda, Davis Alan, Finan Patrick, Gwenn Smith, James Pekar, Peter Barker, Roland Griffiths, Frederick Barrett

Johns Hopkins University School of Medicine, Baltimore, Maryland, United States

Background: Psilocybin has shown promise for the treatment of major depressive disorder, a disorder often accompanied by cognitive rigidity. One mechanism by which psilocybin could reduce depressive symptomology is by increasing cognitive flexibility and neural flexibility, particularly of the anterior cingulate cortex (ACC), a region implicated in depression, psychedelic drug action, and cognitive flexibility.

Methods: In an open-label, waitlist-controlled study of 24 patients with major depressive disorder, we tested the enduring effects of psilocybin therapy on depression, cognitive flexibility, as measured by perseverative errors on a set-shifting task, neural flexibility, as measured by dynamics of functional connectivity (dFC) via functional magnetic resonance imaging, and metabolite concentrations in the ACC, as measured via magnetic resonance spectroscopy.

Results: Psilocybin therapy reduced depression and increased cognitive flexibility for at least four weeks post-treatment, though these improvements were not correlated. One-week after psilocybin therapy, glutamate and N-acetylaspartate concentrations were decreased in the ACC, and dFC was increased between the ACC and the posterior cingulate cortex (PCC). Surprisingly, these increases in dFC between the ACC and PCC were associated with less improvements in cognitive flexibility after psilocybin therapy. Connectome-based predictive modeling demonstrated that baseline dFC emanating from the ACC predicted improvements in cognitive flexibility. In these models, greater baseline dFC was associated with better baseline cognitive flexibility but less improvements in cognitive flexibility.

Conclusions: These findings show that psilocybin therapy in patients with depression can enhance cognitive flexibility and neural flexibility, especially of the ACC, but suggest a nuanced relationship between neural flexibility and depression symptomology. Whereas some enduring increases in neural dynamics may allow for shifting out of a maladaptively rigid state, larger persisting increases in neural dynamics may be detrimental to the efficacy of psilocybin therapy.

Keywords: Psilocybin, Major Depressive Disorder (MDD), Cognitive Flexibility, Functional MRI (fMRI), Dynamic Functional Connectivity

Disclosure: Nothing to disclose.

P354. Late-Life Depression is Associated With Increased Levels of the Pro-Aging Marker GDF-15

Emma Mastrobattista*, Eric Lenze, Charles Reynolds, Benoit Mulsant, Julie Wetherell, Ana Paula Mendes-Silva, Erica Vieira, Breno Diniz

University of Connecticut, School of Medicine, West Hartford, Connecticut, United States

Background: In the past few decades, there is growing evidence that the growth differentiation factor-15 (GDF-15) plays a significant role in aging and multi-system disease development. The GDF-15 has a largely pleotropic effect and has been associated with both the development of cancers, metabolic, inflammatory, and cardiovascular diseases. Emerging evidence suggest that the GDF-15 is a progeroid protein and that strongly correlates with chronological age, decreases telomerase activity, and increases mortality risk in older adults. Few studies have investigated the association between GDF-15 and neuropsychiatric disorders, with higher levels found in bipolar disorder, MDD, and dementia. However, these studies had small sample sizes and no studies evaluated GDF-15 levels in older adults with major depression.

This study aimed to evaluate the circulating levels of GDF-15 in a large cohort of adults with major depressive episode. Our working hypothesis was that older adults with major depressive episode would have higher GDF-15 levels than non-depressed comparison individuals.

Methods: We included 430 older adults in this analysis, 308 with acute major depressive episode (MDE) and 108 controls (both groups contained male and female participants). These individuals were recruited in 4 different sites (St Louis, San Diego, Pittsburgh, and Toronto, CA). All individuals with MDE were not under antidepressant treatment at the time of psychiatric assessment and blood draw. GDF-15 was measured in the serum using a multiplex immunoassay.

Results: LLD subjects were older, had a higher proportion of females, higher BMI values, and higher medical comorbidity burden. There were no significant differences between groups in other demographic and clinical data. Subjects with LLD had a significantly higher GDF-15 plasma levels compared to the HC subjects (t-test = -6.43, d.f.= 437, p < 0.001). After controlling for potential confounding variables, the association between LLD diagnosis and plasma GDF-15 levels remained statistically significant after controlling for the effect of these potential confounding variables (z = 2.15, p = 0.031).

GDF-15 plasma levels were significantly correlated with age (r = .13, p = .017), BMI (r = .13, p = .009), and CIRS-G score (r = .13, p = <.001). We did not find a significant correlation between GDF-15 and the severity of depressive symptoms measured by the MADRS in the LLD subjects only (r = .13, p = .18). Other characteristics of the depressive episode were also not significantly associated with GDF-15 levels, including recurrence (t-test = -1.3, d.f. =306, p = .194), duration of the depressive episode (r = -.03, p = .67, n = 306), or history of previous suicide attempt (t-test = 1.79, d.f. =428, p = .07). The presence of comorbid anxiety disorders (all and specific anxiety disorder diagnosis) during the depressive episode did not significantly influence the levels of GDF-15.

Conclusions: This study has demonstrated that individuals with LLD have higher circulating levels of GDF-15 and worse medical co-morbidity burden compared to those without LLD. Additionally, GDF-15 levels were not significantly associated with severe-depressive symptoms. Our findings provide additional evidence that major depressive episode in older adults is associated with age-related biological changes and support the hypothesis of an accelerated biological aging in these individuals.

Keywords: Late-Life Depression, GDF-15, Accelerated Aging

Disclosure: Nothing to disclose.

P355. Charting the Proteome Landscape in Major Psychiatric Disorders: From Biomarkers to Biological Pathways to Precision Psychiatry

Brisa Fernandes*, Yulin Dai, Peilin Jia, Zhongming Zhao

The University of Texas Health Science Center at Houston, Houston, Texas, United States

Background: Precision Psychiatry is a recognized priority. Schizophrenia (SZ), Bipolar Disorder (BD), and Major Depressive Disorder (MDD) share many of their underlying biologies, and there is a lack of biological validity in their diagnosis, which is a hindrance to developing diagnostic tests and discovering and developing new drugs that would be a perfect molecular fit to a given person. Proteomic studies have evolved the field by identifying several proteins that could be biomarkers in those disorders; however, their results have varied widely, and individual biomarkers have failed to advance diagnostics and therapeutics. Our goal is to leverage the broad variability among different studies and strengthen the knowledge provided by individual proteins by systematically interrogating the literature to uncover biological pathways with stronger biological meaning.

Methods: This study is a systematic review of all proteomics studies in BD, MDD, and SZ compared to controls in serum or plasma. We extracted all differentially expressed proteins in BD, MDD, or SZ. Protein identification was made according to the UniProt Database. We mapped each protein to its corresponding gene. We then conducted over-representative analysis (ORA) and gene set enrichment analysis (GSEA) in WebGestalt to unveil which biological pathways were shared or unique to each disorder. Analyses were adjusted for multiple testing corrections.

Results: We included 51 studies with 9,423 participants. 486 proteins were found altered in cases compared to controls (192 in SZ; 190 in BD; and 365 in MDD). The majority of the enriched pathways were shared among SZ, BD, and MDD. The top pathways in all three disorders were associated with the immune system and complement cascade. Other pathways shared among SZ, BD, and MDD were interleukin-12 signaling, MAPK1/MAPK3 signaling, PI3K-Akt Signaling, Toll-like Receptor Signaling, Activation of Matrix Metalloproteinases, Class A/1 (Rhodopsin-like receptors), GPCR downstream signaling, Advanced glycosylation end-product receptor signaling, JAK-STAT signaling, and Regulation of Insulin-like Growth Factor (IGF) transport. Pathways shared between SZ and BD were integrin cell-surface interactions and syndecan interactions. Shared between BD and MDD were the NRF2 pathway, signaling by EGFR, and the Ras signaling pathway. Unique to SZ were interleukin receptor SHC signaling, and TFAP2 (AP-2) family regulation of growth factors; unique to MDD were oncostatin M signaling, ECM-receptor interaction, plasminogen activating cascade, and PPAR signaling pathway.

Conclusions: We curated an ensemble knowledge of 486 altered serum proteins in BD, MDD, and SZ and uncovered their biological pathways. Alterations in pathways related to immune-inflammation were pervasive and transdiagnostic. The immunoinflammatory response, as assessed in peripheral blood, is a shared mechanism across SZ, BD, and MDD, which might imply that the periphery is an unspecific representation of a mechanism placed in the brain and probably a secondary phenomenon to a primarily central origin; it also implies that the biological boundaries among SZ, BD, and MDD mostly do not resemble current nosological categories and need to be completely redefined by the identification of new sub-types. Future drug development for SZ, BD, and MDD could target those identified pathways and be tested in transdiagnostic clinical trials guided by the specific biological pathways altered in a particular person.

Keywords: Precision Medicine for Mood Disorders, Bioinformatics, Peripheral Biomarker, Proteomics, Drug Discovery - New Approaches

Disclosure: Nothing to disclose.

P356. A Female-Specific Role for the EphA2 Receptor Within the Prefrontal Cortex in Mediating Depression-Like Behaviours in Rats

Rachel-Karson Theriault, Joshua Manduca, Melissa Perreault*

University of Guelph, Guelph, Canada

Background: Ephrins (Eph) and their associated ephrin receptors are predominantly expressed at excitatory synapses in various brain regions implicated in depression, including the frontal cortex and hippocampus (HIP), and are involved in the regulation of synaptic transmission, dendritic spine morphology and synaptic plasticity. Animal models used for the study of depression suggest that Eph-ephrin signaling in the rodent prefrontal cortex (PFC), particularly through the EphA4 and EphB2 receptors, may be involved in mediating depression-like behaviour. However, the lack of selective pharmacological agents for the other ephrin receptor subtypes has limited our understanding of their role in neuropsychiatric disorders. In this study, using a selective activating peptide for the EphA2 receptor, the functional role of the receptor in regulating anxiety and depression-like behaviour in male and female rats was evaluated. As we have previously shown that neuronal oscillatory activity is coupled to depression-like behaviours in a sex-specific manner, the sex-specific impact of EphA2 receptor activation on neuronal system function was also determined.

Methods: Male and female Wistar rats were bilaterally implanted with cannulae into the PFC, concomitant with stainless steel electrode implantation in the cingulate cortex (Cg), nucleus accumbens (NAc), and dorsal HIP. To target the EphA2 receptor, a selective EphA2 nanomolar peptide ligand agonist (5 nM solution, 1µl/side) was used. Following recovery, animals underwent a 7-day protocol to evaluate the impacts of EphA2 receptor activation on behaviour and neuronal oscillatory activity. Rats were administered an infusion of the EphA2 peptide agonist or vehicle 15 minutes prior to each behavioural test (no more than one infusion/test per day) that included the forced swim test (FST), sucrose preference test (SPT), or elevated plus maze (EPM). On a different day, local field potential recordings were performed in awake animals in clear plexiglass boxes. Recordings were collected for 15-minutes prior to the intra-PFC infusion with the assigned treatment (baseline) and for 45-minutes immediately post-infusion. At the end of the study, brains were removed for subsequent protein expression analysis in the PFC by Western Blot.

Results: Only female animals displayed significantly increased immobility time (P < 0.001) and reduced latency to immobility (P = 0.002) in the FST following EphA2 receptor peptide administration. Similarly, in the EPM, only females exhibited a significant reduction in time spent in the open arms (P = 0.02) and the number of open arm entries (P = 0.028) post-fusion. Behaviour in the SPT was not altered in either sex. Female rats that received an intra-PFC infusion of the EphA2 receptor peptide exhibited significantly greater HIP delta power (P = 0.01) and lower HIP theta power (P = 0.004) compared to vehicle infused females. This same pattern was observed within the NAc of male rats, with those that received an EphA2 receptor peptide infusion having displayed greater delta (P = 0.015) and lower theta power (P = 0.003), compared to vehicle infused males. No significant effects of treatment on low frequency band power in the Cg were observed in either sex. In the high frequency bands, the only observed difference was lower high gamma power within the NAc of EphA2 receptor peptide infused female rats compared to control females. When coherence was examined, female rats that received an infusion of the EphA2 receptor peptide exhibited greater theta coherence than vehicle infused females between the Cg-NAc (P < 0.001) and Cg-dHIP (P = 0.005). Between the NAc-dHIP, both male (P = 0.017) and female (P = 0.006) animals infused with the EphA2 receptor peptide had greater delta coherence compared to the sex-matched vehicle infused animals. Across the high frequency bands, no significant effects of treatment in either sex were observed between the Cg-NAc or Cg-dHIP. However, between the NAc-dHIP, EphA2 receptor peptide infusion in males induced greater beta coherence (P = 0.007) than vehicle infusion. Total PFC EphA2 receptor expression was not altered by drug treatment. However, the level of phosphorylated ephexin-1, a downstream substrate of the EphA2 receptor, was significantly elevated in the PFC of females only upon EphA2 receptor activation. No drug-induced differences in total PFC ephexin-1 or RhoA expression were found in either sex or treatment group. N = 8-10/group.

Conclusions: These preclinical findings identify key sex differences in the molecular, neurophysiological and behavioural outcomes of PFC EphA2 receptor activation. Specifically, whereas PFC EphA2 receptor activation increased ephexin-1 activity and induced depressive- and anxiety-like behaviour in the female rats, no such effects were evident male rats. The effects of PFC EphA2 receptor activation on spectral power and coherence were predominantly focused within the low frequency range in both males and females, but showed distinct regional specificity depending on the sex. Further, the increased theta coherence involving the Cg were observed selectively in the female animals. Overall, these findings implicate EphA2 receptor-ephexin-1 signaling in the PFC as potentially having a unique female-specific role in regulating behaviours that may have relevance to depression, and further, highlight the critical need for the inclusion of sex as an experimental variable in research.

Keywords: Anxiety and Depression, EphA2 Receptor, Neuronal Oscillations, Ephrin

Disclosure: Nothing to disclose.

P357. Stress-Induced Alterations in Neural Responsivity to Food Reward Cues in Unmedicated Individuals With Variable Appetite/Weight Phenotypes of Major Depressive Disorder

Laura Holsen*, Hyeon Min Ahn, Julia Hall, Jill Goldstein, Daniel Dillon, Diego Pizzagalli

Harvard Medical School, Boston, Massachusetts, United States

Background: Divergent phenotypes in major depressive disorder (MDD) related to appetite and weight change are largely understudied from a mechanistic perspective, despite evidence of differences in clinical outcomes and morbidity. Compared to those with hypophagic depression (HypoMDD; decreased appetite/weight loss during an episode), individuals with hyperphagic depression (HyperMDD; increased appetite/weight gain) exhibit greater suicidality and medical comorbidities, with recent data suggesting that hyperphagic behaviors stem in part from disruption in mesolimbic regions governing reward. In rodents, chronic social defeat stress (a paradigm resulting in depressive-like behaviors) can result in the emergence of a phenotype similar to HyperMDD, with elevated food intake and weight gain in response to stress. These data provide preclinical evidence of interactions between stress and reward that might be implicated in the pathophysiology underlying endophenotypes of MDD. The current study examined the effects of a robust psychosocial stressor and a matched, non-stressful protocol on mesolimbic reward and stress circuitry responsivity to a food incentive delay (FID) task (measuring reward anticipation and feedback) in individuals with HyperMDD, HypoMDD, and healthy controls.

Methods: We studied 90 adults [40 healthy control (HC; 20F/20M), 29 unmedicated Hypophagic MDD (HypoMDD; 15F/14M); 21 unmedicated Hyperphagic MDD (HyperMDD; 9F/12M)], each of whom completed 2 study visits (~1 week apart) involving serial blood sampling (for cortisol), completion of the Maastricht Acute Stress Task (MAST; an acute psychosocial stressor; Stress Visit) or a non-stressful version of the MAST (Control Visit; visit order counterbalanced), MRI scanning (FID task) on a Siemens 3T Skyra, and questionnaires (Perceived Stress Scale to assess current perceived life stress and the Snaith-Hamilton Pleasure Scale to measure hedonic capacity). Changes in cortisol, reaction time (RT) during the FID task, brain activity, and brain-behavior relationships were examined in the context of response to psychosocial stress. fMRI data were analyzed using SPM12 using a full factorial design to examine main effects of Group and Visit, and Group x Visit interaction effects for two contrasts of interest: food reward anticipation vs. neutral anticipation; food reward receipt vs. neutral success. ROI analyses, with an a priori threshold of p(FWE-corrected)<0.05, examined effects in the hypothalamus, nucleus accumbens, caudate, amygdala, hippocampus, and ventromedial prefrontal cortex (VMPFC).

Results: For cortisol responsivity, a repeated measures ANOVA showed a Time x Visit interaction (F = 54.72, p < 0.001), driven by higher cortisol response to the MAST at Time 20 (immediately following the MAST) vs. Time 0 (immediately preceding the MAST) during the Stress Visit, but not at the Control Visit. For RTs during the FID, analyses indicated a main effect of Group (F = 3.41, p = 0.02), driven by faster RT in HyperMDD vs. HC (p = 0.002), and a trend for faster RT in HyperMDD vs. HypoMDD (p = 0.07). We also found a main effect of Cue (F = 5.08, p = 0.03), driven by faster RT when subjects responded on Food vs. Neutral cues. During the FID, for anticipation of food reward vs. neutral, there a main effect of Group in the VMPFC (F = 12.26, p = 0.007), driven by greater activation in HC vs. HypoMDD (p = 0.001) and in HC vs. HyperMDD (p = 0.0009); HypoMDD and HyperMDD groups did not differ (p = 0.31). VMPFC activation was negatively associated with perceived stress scores across groups (r = -0.35, p = 0.001). There was also a main effect of Visit in the caudate (F = 16.03, p = 0.047), driven by attenuated activation during the Stress Visit vs. Control Visit (p = 0.002). Caudate activation during the Stress Visit (but not the Control Visit) was positively associated with hedonic capacity across groups (r = 0.3, p = 0.008). There was also a Group x Visit interaction in the amygdala (F = 8.14, p = 0.032) and at a trend level in the hypothalamus (F = 6.28, p = 0.06). In the amygdala, the interaction resulted from hypoactivation in the HyperMDD group (relative to HC and HypoMDD) during the Stress Visit vs. hyperactivation (relative to HC and HypoMDD) during the Control Visit. In the amygdala, the HC and HypoMDD groups did not show differences in activation between Visits. In the hypothalamus, the HC group exhibited hyperactivation (relative to both MDD groups) during the Stress Visit vs. hypoactivation (relative to both MDD groups) during the Control Visit. For receipt of food reward vs. neutral, there was main effect of Visit in the hypothalamus (F = 9.35, p = 0.05), resulting from attenuated activation during Stress vs. Control Visit.

Conclusions: These data indicate an effect of psychosocial stress on behavioral reward sensitivity across groups, and in particular in response to food cues in the HyperMDD. In addition, findings elucidate stress-induced alterations of brain activity in mesolimbic circuitry in response to psychosocial stress in appetite phenotypes of MDD, particularly in the amygdala. Stress-induced amygdala hypoactivation during anticipation of food reward in HyperMDD provides evidence in support of a reward deficit model of aberrant neural response to food rewards, a potential mechanism for stress-induced overeating in this group. These findings provide insight into novel neuroanatomical targets in the development of treatments for HyperMDD and related conditions, such as anorexia nervosa and obesity.

Keywords: Acute Stress, Reward, Major Depressive Disorder (MDD), Appetite, Cortisol Response to Stress

Disclosure: Nothing to disclose.

P358. Genetics and Brain Imaging Show a Role for NFIA in Astrocytes in Suicide Attempt

Junsung Woo, Consuelo Walss-Bass, Benjamin Deneen, Ramiro Salas*

Baylor College of Medicine, Houston, Texas, United States

Background: Although genetics and human brain imaging are collecting data at tremendous speed, the accumulation of this information does not always result in a much better mechanistic understanding of the studied phenotypes. One reason is that genetics and human brain imaging tend to work in isolation. We developed ProcessGenesList (PGL), a strategy to use the aggregated mRNA expression levels of groups of genes known or suspected to be associated with a certain disorder, symptom, or phenotype to generate human brain imaging study hypotheses. We applied PGL to suicide to study a) which brain regions are altered in humans with past suicide attempt, b) genetic interactions (single nucleotide polymorphisms, SNPs) with brain imaging characteristics in the setting of past attempt (ATT), c) ex-vivo human tissue to verify those interactions using immunohistochemistry, and d) mouse mutant models to study possible mechanisms and to drive additional human studies.

Methods: PGL: We used all SNPs with p = 10-3 or less from a suicide attempt GWAS (Willour, 2012) and averaged the mRNA expression of the associated genes in all brain regions studied in the Allen Atlas. We obtained 8 brain regions for further study. Brain imaging: We used a sample of 423 inpatients at The Menninger Clinic in Houston, TX (133 with past attempt). We used resting state functional connectivity (Conn analysis tool) and morphometry (FreeSurfer). Human genetics: SNPs were studied by PCR. Ex-vivo: We used amygdala tissue punches from 10 suicide decedent brains and 10 controls. Mouse: We used NFIA loss of function in the amygdala for immunohistochemistry, electrophysiology, and genetic studies.

Results: Using PGL we found 8 brain regions for further study, including the subiculum and the corpus callosum. When studied using resting state functional connectivity, ATT patients showed increased subiculum/habenula and subiculum/dorsolateral prefrontal cortex (which interacted with APAK7 genotype). We studied the corpus callosum with FreeSurfer and found that the anterior region was larger in ATT patients, but only if the rs2474388 in NFIA SNP was GT/GG. In ex-vivo amygdala tissue, NFIA was shown to significantly be overexpressed in suicide decedent brains (P < 0.001). In mice, NFIA amygdala loss of function showed lower MAO-B and lower GABA, abnormal excitation/inhibition patterns in astrocytes, and reduced fear conditioning and anxiety-like behaviors. We then studied MAO-B in ex-vivo tissue and found increased MAO-B.

Conclusions: We showed that a) PGL resulted in hypotheses that when studied uncovered brain features altered in ATT (subicular connectivity and callosal volume), b) Subicular connectivity interacted with AKAP7 genotype, and callosal volume interacted with NFIA genotype, c) NFIA (important in astrocyte function in the amygdala) expression was increased in suicide decedent brain amydgala, d) mice with amygdalar NFIA loss-of-function had astrocyte abnormalities, decreases in MAO-B and GABA, and low fear and anxiety-like behaviors, finally, e) the mouse study informed an additional ex-vivo study and we foun increased MAO-B in decedent brain amygdala tissue.

Keywords: Suicide Attempt, Astrocytes, Resting State Functional Connectivity, NFIA

Disclosure: Nothing to disclose.

P359. Are Symptoms and Function Distinct Depression Treatment Targets in the Real World?

Augustus Rush, Soon Nan Wee, Miguel Renteria, Scott Kollins*

Holmusk, New York, New York, United States

Background: Treatment for depression aims to minimize disease severity and optimize daily function, while mitigating relapse, self-harm, and secondary complications (e. g. substance use disorders or general medical conditions). Yet, efficacy trials focus almost exclusively on symptoms, which are insufficient outcomes for the roughly 1 in 3 depressed patients who cannot achieve sustained symptom remission. This analysis examines the relationship between overall function and a measure of overall disease severity in a large real-world sample of depressed outpatients.

Methods: Data were derived from a large Electronic Health Record (EHR) collected between 2007-2020 that encompassed 24 mental health care systems in which 422,731 patients were treated in both in- and outpatient treatment settings. The analytic sample consisted of adult outpatients (> 18 years) with a recorded ICD-9/10 diagnosis of non-psychotic Major Depressive Disorder with at least 1 baseline and 2 post-baseline outpatient visits at which both the Global Assessment of Function (GAF; Range:1-100 with higher numbers reflecting better function) and the Clinical Global Index of Severity (CGI-S; Range:1-7 with higher numbers reflecting worse disease severity) were collected. Given the nature of the data source, this analysis was exempt from IRB review.

For predictive and discriminative analyses, we divided patients into those with improved (I) (lower) or worsened (W) (higher) CGI-S scores between baseline and the 2nd post-baseline visit, eliminating those without change in the CGI-S. Spearman’s rho correlations and decision tree regression analyses defined the relationship between the CGI-S and GAF cross-sectionally and as change measures between visits for both cohorts. Bivariate, multivariable and mediation analyses were conducted to understand the effect of clinical and socio-demographic variables (e. g. gender, age, race, employment status, gender and comorbid diagnosis) on the relation between GAF and CGI-S.

Ordinary least-squares models (OLS) were built to determine whether using either CGI-S, 10-point GAF groups (defined a priori as a meaningful change) or the combination could discriminate between those with at least 2 baseline comorbid psychiatric illnesses (the median for both cohorts) from those with fewer or predict time between the baseline and the next post-baseline visit.

Results: Altogether 1,265 patients formed the analytic sample for the I cohort; and 2,941 formed the W cohort. Cross-sectional correlations between CGI-S and GAF at baseline, 2nd and 3rd visits were -0.38, -0.39, -0.38; and -0.53, -0.53 and -0.52 for the I and W cohorts, respectively. Further, the correlation between change in scores from baseline to 3rd visit were -0.04 and -0.24 for the I and W cohort respectively.

No changes in CGI-S scores were able to predict a meaningful (at least 10-points) change in the GAF based on the decision-tree regression models for either cohort. In the I cohort, a > 3-point decrease in CGI-S predicted a 3.6-point increase in GAF, while a 2-point decrease in CGI-S predicted a 6.8-point increase in GAF. Decision rules obtained from the W cohort predicted a 6.6-point decrease in GAF from a 2-point increase in CGI-S but predicted an 8.6-point decrease in GAF from a > 3-point increase in CGI-S.

Several factors (e. g. race, employment status, psychiatric comorbidities, neuro-degenerative and substance use disorder) had statistically significant indirect effects on GAF and CGI-S for both worsened and improved CGI-S cohorts. However, the magnitude of change in CGI-S from these variables in relation to the GAF was very small (<=0.31-point change in CGI-S).

Discriminant analysis on both cohorts showed weak discriminant ability of CGI-S, GAF or the combination to discriminate between patients with high comorbid illness load. AUC scores using CGI-S, 10-point GAF group and its combination were 0.57, 0.57 and 0.58 for the I cohort and 0.55, 0.57 and 0.58 for the W cohort.

For predictive analysis, using both CGI-S and 10-point GAF groups within the model improved predictive ability when compared to using either CGI-S or GAF alone for both cohorts, (p < 0.001) though overall predictive ability was low (R2 = 0.014, 0.063, 0.065 for CGI-S, GAF, combination in the improved cohort and 0.016, 0.017 and 0.022 for the worsened cohort).

Conclusions: For MDD patients that improved and for those that worsened, the CGI-S and GAF total scores were only modestly correlated at each visit and as between-visits change measures. A non-linear and asymmetrical relation was found between CGI-S and GAF. Socio-demographic variables did not meaningfully affect the relationship between changes in these two measures. The combination of both measures performed only modestly better than either alone in predicting between visit times and in discriminating between those with more or fewer psychiatric comorbidities. The CGI-S and GAF measure distinct constructs, suggesting that they may be useful as composite or compound outcome measures, especially in persons with difficult to treat depressions.

Keywords: Major Depressive Disorder (MDD), Functioning, Depressive Symptoms

Disclosure: Holmusk: Employee (Self)

P360. Sex and Brain Region Differences in Microglia-Specific Gene Expression

Marianne Seney*, Ryan Logan, Zachary Freyberg, Kelly Barko, Sadie Riskus

University of Pittsburgh Medical Center, Western Psychiatric Institute and Clinic, Pittsburgh, Pennsylvania, United States

Background: Microglia are the resident macrophages of the brain, performing many roles related to brain homeostasis, including modulation of synapses. In the healthy adult brain, microglia exhibit a ramified morphology, sampling the local environment by extending and retracting processes. Various stimuli, including infection, trauma, or altered neuronal activity, induce changes in microglia shape, gene expression, and function; these microglia take on an amoeboid shape and are called “reactive”. In this reactive state, microglia may engulf and eliminate synaptic material. Although this process occurs during development to sculp circuits and in an activity-based manner in adults to modulate neuronal activity and synaptic plasticity, excess reactive microglia may contribute to pathological elimination of synapses/dendritic spines in disease. Studies assessing morphological features of microglia found regional differences as well as sex differences in some brain regions. Transcriptomics studies of isolated microglia also suggest differences based on brain region and sex. However, markers used to isolated microglia in these studies (e.g., CD11b, Cx3cr1) are not expressed exclusively by microglia, but are expressed by resident and infiltrating macrophages. Here, we assessed the transcriptional profile of microglia after sorting with the microglia-specific marker TMEM119, with a specific focus on whether the transcriptional profile varied by brain region and/or sex.

Methods: Adult mice (n = 6/sex; 10-15 weeks old), heterozygous for Tmem119-2A-CreERT2 and Ai14(RCL-tdT)-D were used. Mice were group-housed in 12-hour light/dark with food and water ad libitum. Mice were administered 75mg tamoxifen/kg body weight via intraperitoneal injection once every 24 hours, for five days. Mice were sacrificed 10-21 days post final injection. Prefrontal cortex (PFC) was isolated from sections at Bregma +2.96 to +1.42 mm, striatum from sections at +1.42 to -0.46 mm, and midbrain from sections at -2.06 to -3.88 mm. Individual cell suspensions were generated of harvested tissue using Miltenyl Biotec Adult Brain Dissociation Kit. Fluorescent activated cell sorting was used to isolate tdTomato labeled microglia. RNA was extracted from isolated microglia using Nextera XT DNA Library Preparation Kit and RNA was sequenced using SMARTer-seq v4 Ultra-low Input Kit. Data was analyzed using DESeq2, with p < 0.05 and fold change>1.2 considered differentially expressed (DE). Pathway overrepresentation was assessed using Metascape and IPA with expressed transcripts as background.

Results: We found striking differences in microglia-specific gene expression between brain regions. Genes that were more highly expressed in microglia isolated from midbrain compared to PFC (886 genes) and striatum (728 genes) were enriched for pathways related to immune function (e.g., adaptive immune response, inflammatory response, response to interferon beta). Notably, midbrain isolated microglia had a transcriptional profile consistent with disease associated microglia, with higher expression of Cd68, Timp2, Clec7a, for instance, and lower expression of P2ry12 and P2ry13. Genes more highly expressed in microglia isolated from PFC vs midbrain (865 genes) and vs striatum (500 genes) were enriched for pathways related to synapses (e.g., postsynapse, synapse organization). Genes more highly expressed in microglia isolated from the striatum vs midbrain (949 genes) were enriched for pathways related to neurons and synapses (e.g., axon, modulation of chemical synapse) and genes more highly expressed in microglia isolated from the striatum compared to the PFC (818 genes) were enriched for pathways related to mitosis and the extracellular matrix (e.g., microtubule spindle mitotic, extracellular matrix structure).

We also found sex differences in expression of microglia-specific genes in all 3 brain regions. In the midbrain, DE genes (366) were enriched for pathways related to cell cycle regulation, long-term synaptic depression, and response to selenium ion, with RORα and RORc as top predicted upstream regulators. In the PFC, DE genes (517) were enriched for estrogen-mediated S-phase entry and altered T and B cell signaling, with Jak1/2 as predicted upstream regulator. In the striatum, DE genes (547 genes) were enriched for IL17 signaling, VEGF signaling, and response to selenium ion pathways, with DLG1 as a top predicted upstream regulator. Interestingly, in the striatum, several genes related to MAP kinase phosphatase activity (e.g., several Dusp genes) were more highly expressed in male-isolated microglia.

Conclusions: These results suggests both brain region and sex differences in the transcriptional profile of isolated microglia. Notably, microglia isolated from the midbrain exhibit a transcriptional profile consistent with being disease-associated microglia compared to microglia isolated from the PFC or striatum. Sex differences in the transcriptional profile of microglia may contribute to reported sex differences in microglia morphology, and our studies suggest potential upstream regulators. Future studies will assess the effects of stress on microglia gene expression, with a specific focus on whether stress elicits brain region- or sex-specific effects.

Keywords: Microglia, Sex Difference, Transcriptomics

Disclosure: Nothing to disclose.

P361. Sex Differences in Omega-3 Fatty Acids for MDD With High Inflammation

Mark Rapaport*, David Mischoulon, Boadie Dunlop, Andrew Nierenberg, Becky Kinkead, Stefania Lamon-Fava, Pamela Schettler, Thomas Ziegler, Maurizio Fava

Huntsman Mental Health Institute, Salt Lake City, Utah, United States

Background: Epidemiological, biomarker, and some clinical trials suggest that eicosapentaenoic acid (EPA)-enriched n-3 fatty acids ameliorate depressive symptoms for some patients with major depressive disorder (MDD). A preliminary study demonstrated that overweight-obese patients with depression and high inflammatory markers were the most likely to benefit from n-3 therapy. A secondary analysis of these data also indicated that there were sex differences in the association between body mass index (BMI) and inflammatory markers, with high inflammation being associated with high BMI in women, but not men. In a follow-up study, we evaluated the dose response effects of n-3 fatty acids on depression in subjects with MDD, high BMI, and high inflammation. Subjects randomized to 4 g EPA daily were more likely than placebo to achieve sustained response on the IDS-C. As an exploratory study, we evaluated sex differences in baseline measures of inflammation, change in n-3 levels, and antidepressant response.

Methods: This 2-site (MGH-Emory), UG3-funded study recruited subjects with MDD (IDS-C scores ≥ 25), BMI > 25 and hs-CRP levels > 3 mg/L. Sixty-one subjects (46 women and 15 men) were randomized to oral placebo, 1 g, 2 g, or 4 g of EPA daily for 12 weeks. Capsules contained approximately 1000 mg n-3 fatty acids, with an EPA:DHA ratio of 4:1. The primary endpoints were a sustained (weeks 8 and 12) decrease in level of plasma IL-6 or LPS-stimulated peripheral blood mononuclear cell TNF-a levels (effect size [ES] > 0.4) for n-3 vs. placebo. Secondary endpoints were a decrease in mean IDS-C scores with ES > 0.35 for any dose of EPA vs. placebo and a sustained response with ES > 0.35 for any dose of EPA vs. placebo. Exploratory measures included changes in hs-CRP.

Results: As previously demonstrated, there were sex differences in the association between BMI and inflammatory markers, with high inflammation being associated with high BMI in women, but not men. In contrast, other than hs-CRP which was significantly higher at baseline in females (p = 0.006), there were no sex differences in baseline levels of other plasma cytokines or n-3 levels. For the overall study, subjects randomized to 2 g and 4 g EPA daily were more likely than placebo to achieve sustained response (at both week 8 and 12) on the IDS-C, with odds ratios (OR) of 2.3 and 3.4 respectively (exceeding the hypothesized ES > 0.35). Response in the 4 g EPA group was primarily driven by females with 75% responding vs 25% for males. Exploratory analysis of hs-CRP levels demonstrated a statistically significant decrease over time with the 4 g dose. The increased response in females vs males was associated with a significantly greater change in plasma EPA (p = 0.008), a greater decrease in plasma hsCRP, and greater change in 18-HEPE, a pro-resolving lipid metabolite of EPA.

Conclusions: These data extend our previous findings that a subset of women with MDD are more likely to have elevated biomarkers of inflammation than men and suggest that there may be sex differences in the response to high dose n-3 in subjects with MDD. Larger confirmatory studies are needed to discern if women manifesting MDD and elevated biomarkers of inflammation represent a subset of patients who are uniquely responsive to high dose n-3 therapy.

Keywords: Depression Inflammation Cytokine, Lipids, Sex

Disclosure: Nothing to disclose.

P362. Epigenetic GrimAge Acceleration in Bipolar Disorder

Camila N. C. Lima, Giselli Scaini, Valeria A. Cuellar, Consuelo Walss-Bass, Jair Soares, Joao Quevedo, Gabriel R. Fries*

University of Texas Health Science Center at Houston, Houston, Texas, United States

Background: Bipolar Disorder (BD) has been previously associated with functional impairment and accelerated epigenetic aging, although the link between these two variables is still unknown. We aimed to investigate the relationship between epigenetic aging acceleration measures with functioning and clinical outcomes in patients with BD and controls.

Methods: Blood genome-wide DNA methylation (DNAm) levels were measured in BD patients (N = 90) and matched healthy controls (N = 40) with the Infinium EPIC BeadChip (Illumina). Epigenetic age estimates were calculated using an online tool, including Horvath DNAm age, Hannum DNAm age, PhenoAge, apparent methylomic aging rate (AMAR), and the recently developed lifespan predictor GrimAge. Measures of aging acceleration were estimated by regressing the predicted epigenetic ages on chronological ages and using the residuals as ‘acceleration indexes’ (intrinsic (IEAA) and extrinsic epigenetic age acceleration (EEAA), PhenoAgeAccel, and GrimAgeAccel). The association between multiple epigenetic aging acceleration indexes with clinical variables and functioning status was tested by linear models while controlling for chronological age, sex, race/ethnicity, smoking status, and blood cell count estimates.

Results: All predicted DNAm age clocks were significantly correlated with chronological age. BD was not significantly associated with the Horvath Age acceleration residual, Horvath.IEAA, Hannum acceleration residual, Hannum AMAR, Hannum.IEAA, Hannum.EEAA, or PhenoAgeAccel. However, BD was significantly associated with greater GrimAge acceleration (GrimAgeAccel) in unadjusted (β = 0.18, p = 0.015) and minimally-adjusted models (β = 2.574, p = 0.013, controlled for age, sex, and race), but not after controlling for use of tobacco and blood cell counts (p = 0.345). Greater length of illness (β = 0.205, p = 0.03), any comorbid substance abuse or dependence (β = 2.484, p = 0.011), and medication status (β = -4.454, p = 0.016) significantly predicted GrimAgeAccel in all models. Finally, a greater GrimAgeAccel predicted poorer functional outcomes measured by the Functioning Assessment Short Test and Global Assessment of Functioning (p < 0.05) in both groups.

Conclusions: Epigenetic aging, as measured by the lifespan predictor GrimAge, is accelerated by comorbid substance use and longer length of illness in BD, with a protective effect of medication. Moreover, this acceleration may contribute to functional decline in patients with BD.

Keywords: Bipolar Disorder, Accelerated Aging, Epigenetic Age Acceleration, DNA Methylation, Functioning

Disclosure: Nothing to disclose.

P363. Polygenic Risk as a Predictor of Bipolar Related Mood Disorder in At-Risk Offspring

Danella Hafeman*, John Merranko, Alyson Zwicker, Benjamin Goldstein, Tina Goldstein, David Axelson, Kelly Monk, Mary Beth Hickey, Dara Sakolsky, Satish Iyengar, Rasim Diler, Vishwajit Nimgaonkar, Rudolf Uher, Boris Birmaher

University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Background: Bipolar Disorder (BD) is highly heritable, but mechanisms of this heritability are still unknown. Polygenic risk scores (PRS) are quantitative markers of risk constructed from large genome-wide association studies (GWAS) that can be calculated on the individual level. We previously built a risk calculator using clinical and demographic variables to predict new-onset BD within offspring of parents with BD. Here, we assessed whether PRS for BD (BD-PRS) predicted new-onset BD and mood disorder in at-risk youth, after accounting for other predictors, and whether adding BD-PRS to a risk calculator improved prediction capability. These findings build on a recent analysis of these data (submitted for publication) showing that BD-PRS was specifically elevated in the parents with BD and at-risk offspring, particularly those with mood disorders. In contrast to the previous analysis, the current work focuses only on effects of BD-PRS within at-risk offspring.

Methods: We calculated BD-PRS scores on a subset of offspring at familial risk in the Pittsburgh Bipolar Offspring Study (BIOS), a longitudinal study of offspring of parents with bipolar disorder I/II and community controls that have been assessed approximately every two years for over twelve years. Since large-scale genome-wide association studies used to derive BD-PRS scoring have been limited to white individuals, we limited our sample to 256 white offspring of parents with bipolar disorder with sufficient genetic data. We first assessed the degree to which, in this at-risk population, BD-PRS predicted bipolar spectrum disorder (BSD; including BD-I, BD-II, and Other Specified BD) in offspring, and whether there were any interactions with other predictors of interest. Next, we assessed whether BD-PRS predicted any mood disorder, since depression may also be related to BD in at-risk samples. Finally, in previous work, we have developed a risk calculator to predict BSD based on subthreshold clinical symptoms, parental age of onset, global functioning, and age; here, we assessed the degree to which BD-PRS improved this risk calculator to predict BD and mood disorder onset.

Results: Within the 256 offspring of parents with BD, 16 had BSD at intake and 42 developed BSD over the course of follow-up; 36 had mood disorders at intake and 82 developed mood disorders over follow-up. Within the at-risk offspring, the BD-PRS was marginally associated with lifetime BSD (HR = 1.22, p = 0.1) and new-onset BSD (HR = 1.28, p = 0.07). There was a significant interaction (p = 0.01), whereby BD-PRS was a significant predictor of new-onset BD in offspring of parents with early-onset BD (age < 18; HR = 1.49, p = 0.007), but not later onset BD (HR = 0.6, p = 0.1). A similar pattern was observed with lifetime BD (interaction p = 0.09). Higher BD-PRS was associated with a marginally increased rate of developing mood disorders, regardless of parental age of onset (HR = 1.23, p = 0.06). However, this increase was not observed across follow-up, but rather limited to age >18 (interaction p = .01; offspring <18 years old: HR = 1.00, p = 0.98; offspring >18 years old: HR = 1.87, p = 0.003). BD-PRS alone had AUCs of 0.57 (0.48-0.67) and 0.59 (0.55-0.62) for new-onset BSD and mood disorder, respectively. In these youth, the original risk calculator for BSD had an AUC of .77 (0.70-0.84); adding BD-PRS, allowing interactions with parental age of onset and age, yielded an AUC of .80 (0.73-0.87). Regarding prediction of mood disorder, the original risk calculator (developed for BSD) had an AUC of 0.78 (0.73-0.82); adding BD-PRS, allowing interactions with parental age of onset and age, did not improve the AUC.

Conclusions: We find that BD-PRS is marginally predictive across the sample of at-risk youth, but that it interacts with other predictors (i.e., age, parent age of onset) to predict more strongly in certain subgroups. Specifically, BD-PRS predicts new-onset BSD only in offspring of parents with early-onset BD; we hypothesize that this may either be because (1) we have not followed the sample long enough to observe the effect of BD-PRS in the offspring of parents with late-onset BD (who may be more likely to have later-onset BSD themselves) or (2) late-onset BD is not as likely to be transmitted via polygenic risk. In contrast, no such interaction is observed with mood disorders (including BSD and depression), where BD-PRS is associated with mood disorder across the sample, but not until adulthood. While BD-PRS generally has poor predictive power for both BSD and mood disorders, combined with other clinical factors, BD-PRS marginally adds to the predictive power of the risk calculator for BSD.

Keywords: Bipolar Disorder, Polygenic Risk Score, Familial Risk, Risk Calculator

Disclosure: Nothing to disclose.

P364. Brain Structure Associated With Future Suicide Thoughts and Behaviors in Female Adolescents With Bipolar Disorder

Lejla Colic, Luca Villa, Maria Dauvermann, Laura van Velzen, Anjali Sankar, Danielle Goldman, Priyanka Panchal, Jihoon Kim, Lianne Schmaal, Anne-Laura van Harmelen, Hilary Blumberg*

Yale School of Medicine, New Haven, Connecticut, United States

Background: Suicide thoughts and behaviors (STBs) often emerge during adolescence. Rates are higher in adolescent females and the majority of adolescents who die by suicide have a mood disorder. While neuroimaging studies of adolescents with mood disorders are emerging, these are primarily investigations of associations to prior STBs which could reflect consequences of the prior STBs rather than represent risk for future STBs. In a collaboration of the international neuroimaging HOPES (Help Overcome and Prevent the Emergence of Suicide) consortium, grey and white matter structure was investigated in female adolescents with and without future STBs.

Methods: The study sample included 92 female adolescents with bipolar disorder or major depressive disorder. Structural and diffusion-weighted magnetic resonance imaging was performed and data processed using Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA) consortium pipelines. STBs were assessed on average two years later to provide subject assignment to three groups: a group with future suicide behavior (fSB, n = 40), a group with future suicidal thoughts (fST, n = 33) and a group without future STBs (fnonSTB, n = 19). One-way analyses of covariance comparing baseline grey matter cortical surface area, thickness, subcortical grey volumes, or white matter tensor-based fractional anisotropy across the three groups were performed and were followed by pairwise comparisons in significant regions (p < 0.05).

Results: Compared to fnonSTBs, fSTs and fSBs showed significant decreases in cortical thickness of right inferior frontal gyrus pars orbitalis and middle temporal gyrus and lower fractional anisotropy in left uncinate fasciculus and corona radiata. The fSBs additionally showed lower fractional anisotropy in right uncinate and superior fronto-occipital fasciculi.

Conclusions: Results of this HOPES consortium study support alterations in grey and white matter in brain systems that subserve emotion and other behavioral regulation in risk for future STBs in female adolescents with mood disorders. Differences that extend bilaterally in white matter may contribute to risk for the transition to future suicide behavior. These findings suggest these brain regions and the behaviors they subserve as neurobehavioral targets to understand the developmental pathophysiology of STBs and for the generation of strategies to prevent suicide in female adolescents with mood disorders.

Keywords: Suicide Prediction, Suicide Attempt, Suicidal Ideation, Mood Disorders, MRI

Disclosure: Nothing to disclose.

P365. Incilius Alvarius Cell-Based Synthesis of 5-MEO-DMT

Leonard Lerer, Erik Reynolds, Giovanne Ojeda-Torres, Bernard Lerer*

Hadassah-Hebrew University Medical Center, Jerusalem, Israel

Background: Incilius alvarius (also known as the Colorado River or Sonoran Desert toad) is a source of natural, psychoactive tryptamines including 5-MeO-DMT (5-methoxy-N,N-dimethyltryptamine) and bufotenin. There is growing interest in the psychiatric therapeutic potential of 5-MeO-DMT. Although an optimized chemical synthetic pathway exists for the production of 5-MeO-DMT, there is a need for naturally sourced 5-MEO-DMT to advance research. The parotoid gland of Incilius alvarius also produces a range poorly characterized molecules including bufagenins, bufotoxins and indolealkylamines, possible “entourage molecules” that may have clinical utility. Incilius alvarius is currently under severe ecological pressure due to consumer demand for natural 5-MeO-DMT and habitat loss.

Methods: We anesthetized 2 Incilius alvarius toads and conducted a wedge biopsy under aseptic conditions in conformity with current best practice in the care of laboratory animals. Glandular tissue was identified in the explants, prepared, dissociated and seeded using standard amphibian cell culture protocols in a basal media preparation supplemented with 10% FBS, antibiotics, sugars, hormones and ionic compounds in 24-well cell culture plates. Culture was undertaken in an incubator at 25°C and 5% CO2. Upon confluence, the cells were disassociated and passaged into additional well plates. Media exchange was done every 3-4 days and the culture was maintained for 45 days. Media was analyzed at 12, 14 and 36 days for the presence of 5-MeO-DMT using a Xevo TQ-S tandem mass spectrometry and UPLC system (Waters Corporation, Milford MA, USA).

Results: Dried media from the cell culture had a light tan appearance that was similar to the known appearance of dried Incilius alvarius parotoid secretion. HRMS/MS fragmentation showed conformity in structure with 5-MEO-DMT. UPLC showed a purity of 16-22% (within the reported range of 5-MeO-DMT concentration in Incilius alvarius parotoid secretion).

Conclusions: To our knowledge, this is the first report of successful production of 5-MeO-DMT from Incilius alvarius parotoid cell culture. These findings constitute preliminary evidence of the feasibility of cell-based 5-MeO-DMT production as a potential source of research and clinical material. The potential availability of “natural” 5-MeO-DMT produced through cellular agriculture, as opposed to the cruel and destructive practice of “milking” Incilius alvarius, also supports efforts to ensure the protection of our planet’s entheogen heritage.

Keywords: Psychedelics, Natural Compound, Dimethyltryptamine

Disclosure: Taliaz, Back of the Yard Algae Sciences: Advisory Board (Self) Hadasit Medical Research Corporation: Patent (Self)

P366. Analgesic and Antinociceptive Effects of the Ketamine Metabolite (2R,6R)-Hydroxynorketamine (HNK) in Mice

Jonathan Yost, Caroline Browne, Irwin Lucki*

Uniformed Services University of the Health Sciences, Bethesda, Maryland, United States

Background: An estimated 20% of adults in the U.S. suffer from an ongoing pain condition, and their pain may cause significant limitations in their work capability, social life, and ability to provide self-care. Severe chronic pain is challenging to treat and increases the risk for developing psychological disorders such as depression. Identifying novel treatment modalities that are effective in alleviating pain is essential to improve clinical treatment and rehabilitation for patients with ongoing pain conditions.

(2R,6R)-hydroxynorketamine (HNK) is a ketamine metabolite that has emerged from laboratory studies as possessing antidepressant effects while lacking the severe side effects of the parent drug. This study examined whether (2R,6R)-HNK may also exert another therapeutic effect of ketamine, analgesia. The results show that (2R,6R)-HNK has the potential to be a safer pain treatment alternative to ketamine that could be made widely available to patients.

Methods: Male and female C57BL/6J mice, age 8-12 weeks, were group-housed (4-5 per cage) in 12-hour light/dark cycles with standard food and water available ad libitum. All drugs were administered via the intraperitoneal route. All experimental protocols were approved by the Uniformed Services University IACUC and were conducted in accordance with the NIH Guide for the Care and Use of Laboratory Animals.

Two measures of pain sensitivity were used. Sensitivity to a noxious thermal stimulus was assessed by measuring the latency to respond once placed upon a hot plate set to 50°C. Localized inflammatory pain was induced in male mice via subcutaneous λ-carrageenan injection into the animal’s hind paw. Mechanosensitivity before and after induction of inflammatory pain was measured by the paw withdrawal threshold using manual von Frey filaments. Carrageenan produced mechanical allodynia within 2 hours that lasted for more than 48 hours. Mice were treated with (2R,6R)-HNK, carprofen, or saline 2 hours following the induction of inflammation.

Results: (2R,6R)-HNK produced antinociceptive effects on the hot plate in male and female mice. The antinociceptive effect was similar for both sexes with onset approximately 10 hours and duration lasting between 24 to 48 hours. Doses of 10-16 mg/kg produced significant antinociception in males, while doses of 10-30 mg/kg were significant in females. The pain reducing effects in both sexes were diminished at doses above 16 and 30 mg/kg in males and females, respectively.

Mice were pretreated with different receptor antagonists to examine the potential mechanism for (2R,6R)-HNK mediated antinociception. The opioid receptor antagonist naltrexone (1 mg/kg) administered 45 minutes before (2R,6R)-HNK had no impact on its antinociceptive effects, but did block morphine-induced antinociception. In contrast, the AMPA receptor blocker NBQX (10 mg/kg) administered 30 minutes before (2R,6R)-HNK prevented its antinociceptive effects, suggesting a glutamatergic mechanism for (2R,6R)-HNK antinociception.

In the inflammatory pain condition, (2R,6R)-HNK produced a reversal of mechanical allodynia in male and female mice at doses of 10 and 30 mg/kg. The onset for inflammatory analgesia was less than 1 hour with a duration greater than 24 hours following a single injection. In a separate experiment with male animals only, the pain reduction effects of (2R,6R)-HNK (10 mg/kg) were compared with carprofen (5 mg/kg), a NSAID typically used to treat inflammatory pain. The effect of (2R,6R)-HNK was comparable with the effects of carprofen on the reversal of mechanical allodynia.

Conclusions: These results demonstrate that (2R,6R)-HNK produces pain reduction under two conditions, antinociception in healthy mice and reversal of allodynia in mice with an inflammatory pain condition. These findings agree with a previous report showing that (2R,6R)-HNK produced a reversal of hyperalgesia present in preclinical models of postoperative type pain, neuropathic pain, and CRPS type pain (Kroin et al., 2019). The mechanism involves glutamatergic AMPA receptors but not opioid receptors. The characteristics of (2R,6R)-HNK reversal of allodynia shown here demonstrate great promise for its potential in treating inflammatory pain in addition to other types of pain.

Keywords: Pain sensitivity, Analgesia, (2R,6R)-hydroxynorketamine, Anti-inflammatory

Disclosure: Nothing to disclose.

P367. Levomilnacipran but Not Duloxetine Inhibits Norepinephrine Reuptake Throughout its Therapeutic Dose Range in Healthy Male Volunteers

Katerina Nikolitch, Jennifer L Phillips, Pierre Blier*

University of Ottawa Institute of Mental Health Research, Ottawa, Canada

Background: Several medications that potently inhibit norepinephrine (NE) reuptake are effective in the treatment of major depressive disorder (MDD). Norepinephrine reuptake inhibition can also exert therapeutic benefits in attention deficit disorder. Dual serotonin (5-HT)/NE reuptake inhibitors are also first-line treatment for MDD, but for venlafaxine and duloxetine doses higher than those necessary to potently inhibit 5-HT reuptake are necessary to inhibit the NE reuptake process [1-3]. While occupancy of 5-HT reuptake transporters has been reliably assessed using positron emission tomography in humans, there remain specificity issues with the main ligand used to label NE transporters [4]. An alternative approach to assessing NE reuptake is the tyramine pressor response. Despite being a marker of peripheral NE reuptake activity, the latter test correlates well with the capacity of drugs like desipramine, clomipramine, and venlafaxine to inhibit NE reuptake [1-3]. The objectives were to assess: 1) whether levomilnacipran and duloxetine significantly inhibit NE at their minimal effective doses for MDD (40 and 60 mg/day, respectively), and 2) at what dose these two medications begin to significantly inhibit NE reuptake.

Methods: Healthy male participants (18-40 years of age) were initially randomized to take either placebo for 21 days, levomilnacipran (40 mg/day for 7 days, increased to 80 mg/day for 7 days, and then 120 mg/day for 7 days), or duloxetine (60 mg/day for 7 days, 90 mg/day for 7 days, and 120 mg/day for 7 days). Participants could prolong administration periods to allow for adaptation to side effects. The activity of NE transporters was evaluated by assessing the increase in systolic blood pressure (SBP) using iv bolus of 4, 6, and 8 mg of tyramine.

Results: : There were 10 completers in the placebo group, 10 for levomilnacipran, and 9 for duloxetine. Two participants withdrew due to side effects, one in each of the active treatment arms. Tyramine injections produced significant dose-dependent increases in SBP at baseline in all three groups (p < 0.001) and the pressor responses were not modified after 7, 14 or 21 days in the placebo group (p > 0.05). Using post-hoc two-way repeated measures MANOVA, levomilnacipran separated from placebo at 40 mg/day (F1,15 = 32.0, p < 0.0001), whereas duloxetine separated from placebo only at 120 mg/day (F1,11 = 7.5, p = 0.02).

Conclusions: These results confirm that both levomilnacipran and duloxetine have the capacity to block NE reuptake within their therapeutic ranges. However, they differ in their doses necessary to interfere significantly with the NE reuptake process: levomilnacipran acts as a robust NE reuptake blocker from its minimal effective dose for MDD, whereas duloxetine needs to reach its maximal recommended therapeutic dose. Taken together with prior results [1,2], duloxetine can only be considered a dual reuptake blocker when titrated to its maximal recommended dose. Ongoing analyses from this data set will determine the dose at which levomilnacipran begins to engage the 5-HT reuptake process to a physiologically relevant degree.

References:

[1] Turcotte et al. 2001. Assessment of the serotonin and norepinephrine reuptake blocking properties of duloxetine in healthy subjects. Neuropsychopharmacology 24 :511-21.

[2] Vincent et al 2004. Clinical assessment of norepinephrine transporter blockade through biochemical and pharmacological profiles. Circulation 109 :3202-07.

[3] Debonnel et al. 2007. Differential physiological effects of a low dose and high doses of venlafaxine in major depression. Int J Neuropsychopharmacology 10:51-61.

[4] Logan et al 2007. Imaging the norepinephrine transporter in humans with (S,S)-[11C]O-methyl reboxetine and PET: problems and progress. Nucl Med Biol 34:667-79.

Keywords: Selective Serotonin Reuptake Inhibitors (SSRIs), Serotonin and Norepinephrine Reuptake Inhibitor, Levomilnacipran, Duloxetine

Disclosure: Allergan: Grant (Self)

Allergan: Honoraria, Consultant (Self)

P368. Functional Connectivity Predictors of Antidepressant Treatment Outcomes in Late-Life Depression

Warren Taylor*, Ryan Ahmed, Kimberly Albert, Hakmook Kang, Sarah Szymkowicz, Patricia Andrews, Jennifer Vega, Bennett Landman

Vanderbilt University Medical Center, Nashville, Tennessee, United States

Background: Late-life depression is associated with a poor response to conventional antidepressant medications and high recurrence risk. Past work in late-life depression examining predictors of antidepressant outcomes has primarily focused on cognitive performance deficits and structural markers of brain aging. There has been less work examining how measures of intrinsic network functional connectivity (FC) may influence antidepressant treatment outcomes in depressed elders.

Methods: 95 individuals aged 60 years or older with Major Depressive Disorder were enrolled in a single-site, randomized 8-week trial of escitalopram or placebo in a two-to-one ratio. MRI was obtained after a two-week washout of pre-existing antidepressant medications but prior to starting blinded study drug. Resting-state fMRI was analyzed by measuring seed-to-seed functional connectivity in predetermined a priori regions focusing on key intrinsic functional networks including the default mode network (DMN), cognitive control network, and limbic network. Primary analyses utilized mixed models examining depression severity (by MADRS) as the repeated outcome measure. Covariates included time, treatment assignment, age, gender, white matter hyperintensity volume, and seed-to-seed FC. Initial models examined a three-way interaction between time, treatment arm, and FC. If this did not achieve statistical significance, the three-way interaction was removed, and two-way interactions were considered.

Results: Analyses of network FC exhibited the strongest relationships with treatment outcome with DMN regions. In mixed models, a poorer response to treatment was associated with FC in the DMN, including the posterior cingulate cortex (PCC) and left (t = -2.09, p = 0.0372) and right (t = -2.13, p = 0.0364) hippocampi. We further observed relationships with treatment outcome in anterior DMN regions including FC between the medial PFC and left (t = -2.38, p = 0.0179) and right (t = -2.85, p = 0.0055) rostral anterior cingulate cortex (ACC). We similarly observed a relationship between response and FC between the left hippocampus and subgenual ACC (t = 2.19, p = 0.0312). Subsequent exploratory analyses extended these findings, associating treatment response with FC in the cognitive control network, limbic network, and additional DMN regions.

Conclusions: DMN and hippocampal connectivity measures obtained pre-treatment are associated with subsequent treatment response. Further work is needed to determine how brain aging influences these key intrinsic networks in order to decrease the likelihood of responding to treatment.

Clinical trials.gov registry: NCT02332291

Keywords: Depression, rsfMRI Functional Connectivity, Clinical Trial, Geriatric

Disclosure: Nothing to disclose.

P369. A Novel Peripheral Biomarker for Depression and Antidepressant Response

Steven Targum, Boadie Dunlop, Jeffrey Schappi, Anastasia Kotsouris, Runa Baumik, Mark Rapaport, Natalie Rasgon, Mark Rasenick*

University of Illinois College of Medicine, Chicago, Illinois, United States

Background: Previous data suggest that the heterotrimeric G protein, Gsalpha (Gsα) is ensconced predominantly in lipid rafts in subjects with major depressive disorder (MDD), resulting in impaired stimulation of adenylyl cyclase. Both diminished Gsα-adenylyl cyclase coupling and an increase in the proportion of Gsα in lipid rafts have been observed in MDD. Antidepressants accumulate slowly in lipid rafts and evoke translocation of Gsα out of lipid rafts toward a more productive association with adenylyl cyclase, resulting in sustained cAMP elevation and sequelae such as increased brain-derived neurotrophic factor. "Rapid-acting" antidepressant compounds, such as ketamine, have the same effect, but on an accelerated timescale. Thus, we hypothesize that heightened accumulation of Gsα in lipid rafts is a biomarker for depression, and that the translocation of Gsα from those rafts is a biomarker for clinical response to antidepressants. We examined the potential of this biomarker in a small proof-of-concept study of subjects with MDD where it may be harnessed for diagnostic and treatment-prognostic purposes.

Methods: Subjects meeting DSM5 criteria for acute major depressive disorder (MDD) with a minimum HamD-17 score ≥15 and healthy controls were recruited at Emory University school of medicine and consented to collection of blood samples to measure PGE1 activation in platelets (as an indicator of Gsα-adenylyl cyclase coupling) with the AlphaScreen (Perhin Elmer) assay. Subsequently, consenting MDD subjects participated in a 6-week open label antidepressant therapy and were evaluated by HAM-D17 (primary), HAM-D6, MADRS, and subject rated IDS-SR30 at screen and 6 weeks. Blood draws were scheduled at screening for all participants and 6 weeks after antidepressants for the consenting MDD subjects. Comparison of the extent of PGE1 activation of adenylyl cyclase (over "basal") was used to indicate the extent of coupling of Gsα with adenylyl cyclase. Change in the extent of biomarker activation was compared in antidepressant responders (improvement of HAM-D17 ≥ 50% from screen) and non-responders in this small study.

Results: There were 20 subjects with MDD and 45 healthy controls completing the study. At screen, platelet samples examining PGE1 from MDD subjects showed a lower response to PGE1 activation than healthy controls. Eleven of 20 participating MDD subjects were antidepressant responders at 6 weeks. Antidepressant responders showed a marked increase in PGE1 activated adenylyl cyclase at 6 weeks compared to non-responders. Responders revealed a 62.0% improvement of PGE1 activation from the screen assessment in contrast to a -14.1% decrement in the non-responder cohort (ANOVA: F = 5.25; p = 0.03). The calculated effect size was 0.93 for the PGE/Gsα lipid-raft biomarker. Eight of the 11 responders (72.7%) on contrast to 2 of the 9 non-responders (22.2%) improved by at least 30% from the screen assessment in the PGE1 activation analysis (Fisher exact = 0.07), and the positive predictive value of PGE1 activation for response/non-response was 75.0%.

Conclusions: In this small sample, the translocation of Gsα from lipids rafts as reflected by an increase in PGE1 activated adenylyl cyclase was used as a biomarker reflecting cAMP signaling/lipid-raft status of Gsα and was associated with antidepressant response in MDD subjects. These data suggest that a simple, high-throughput capable assay for antidepressant response can be developed and used to create a platform for personalized medicine for subjects with MDD. Future studies will determine whether this biomarker can anticipate antidepressant response early in treatment and prior to the clinical metrics.

Keywords: Cyclic AMP, Lipid Rafts, GPCR, Antidepressant, Biomarker

Disclosure: Pax Neuroscience: Stock / Equity (Self)

P370. Backtranslating Sex Differences in Peripheral Immune Dysregulation From Patients With Major Depressive Disorder to Mice

Jennifer Rainville, Sadie Riskus, Xianging Xue, Alisa Huskey, James Murrough, Marianne Seney, Georgia Hodes*

Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States

Background: Women account for 2/3rds of the 300 million people world-wide who have depression and are more likely to be treatment resistant. Women may present with fundamentally different symptoms of depression supporting the possibility that men are being under diagnosed. In an age of personalized medicine, no current treatments for depression take sex into consideration. Here we examined the relationship between sex, treatment resistant status, symptomatology and circulating cytokines in patients with depression. We back translate our findings into mice and identified key cytokines linked to behavioral endophenotypes that differ within the context of sex.

Methods: We used multiplex ELISA to quantify plasma cytokine protein levels regulated by treatment resistant (n = 27) and non-treatment resistant depression (n = 23) in men and women compared to age matched (21-55 years) healthy controls (n = 28). To test the ability of mouse stress models to recapitulate the cytokine changes found in depressed individuals we examined circulating levels of cytokines for male and female mice exposed to 6 (n = 40) or 28 day (n = 40) variable stress. Cytokines from patients with depression were correlated to subtypes of behavior indicated by the QIDS index. Cytokines from mice exposed to variable stress were correlated with behavioral responses across a test battery that included novelty induced hypophagia, splash test, forced swim test and social interaction.

Results: We found a number of cytokines that were significantly altered by depression vs. healthy controls across depression subtype/ sex including IL10, MCP-1 VEGF, IL-17 and IFN-y . However, most cytokines differed by a combination of treatment resistant status and sex. Women with treatment resistant depression had the largest number of cytokine changes, followed by non-treatment resistant men. Most cytokine changes negatively correlated with concentration in women with treatment resistant depression (p values < 0.05). IL-1a positively correlated with over-eating and weight gain. MCP-1 positively correlated with oversleeping. In contrast, for women who were not treatment resistant, most cytokine changes related to oversleeping/overeating, loss of interest and restlessness (p values < 0.05). In men with treatment resistant depression most cytokine changes related to feelings of restlessness (p values <0.05) and insomnia (GSF/IL12). Many of the cytokines altered in humans were not detectable in mice. However, of those we could detect IL-12p40, GM-CSF, MCP-1 and IL10 were altered by 6-day variable stress. Whereas only IL12p40 was altered by 28 days of stress. Correlations between cytokines and behaviors in mice following stress matched more closely with relationships between cytokines and endophenotypes in humans with depression.

Conclusions: Cytokines changes in blood of patients with depression were driven by the sex and treatment resistant status of the individual. Overall, cytokine levels are predicative of different specific symptomatology of patients with depression and that relationship differed by treatment resistant status and sex. While only a few of the cytokine changes in depressed patients could be altered by stress in rodents, the relationship between cytokines and behavioral endophenotypes could be recapitulated. These data suggest examining cytokine levels within the context of symptomatology and individual differences when identifying accurate biomarkers and treatment targets.

Keywords: Depression Inflammation Cytokine, Stress, Sex Differences

Disclosure: Nothing to disclose.

P371. A Combinatorial Pharmacogenomic Algorithm is Predictive of Sertraline Metabolism in Patients With Major Depressive Disorder

Sagar Parikh, Rebecca Law, Daniel Hain, Anthony Rothschild*, Michael Thase, Boadie Dunlop, Charles DeBattista, Brent Forester, Richard Shelton, Matthew Macaluso, Elizabeth Cogan, Krystal Brown, David Lewis, Michael Jablonski, John Greden

University of Massachusetts Medical School, Worcester, Massachusetts, United States

Background: Pharmacogenomic testing can aid in treatment selection for patients with Major Depressive Disorder (MDD) by identifying gene-drug interactions that may impact medication metabolism. Although there have been rapid advancements in this field, there is not a consensus about the approach to pharmacogenomic testing or even what genes are relevant for many antidepressants. Here we assessed the ability of a combinatorial pharmacogenomic test (weighted assessment of multiple genes) to predict meaningful variations in sertraline blood levels relative to the Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines for CYP2C19.

Methods: All patients were enrolled in the Genomics Used to Improve DEpression Decisions (GUIDED) trial – a large, patient- and rater-blinded, randomized, controlled trial that included patients diagnosed with MDD who had an inadequate response to ≥1 psychotropic medication (N = 1,167). A subset of 124 patients reported taking sertraline within 2 weeks of the screening blood draw and had sertraline blood concentrations quantified using LC-MS/MS. The combinatorial pharmacogenomic test reported a weighted assessment of individual phenotypes based on multiple pharmacokinetic genes relevant for medications included on the test. For sertraline, this included CYP2C19, CYP2B6, and CYP3A4. Medications were categorized according to the predicted level of gene-drug interactions (GDI) and change in metabolism (increase, decrease). Sertraline log-transformed concentration/dose ratios were compared between combinatorial pharmacogenomic test categories and CPIC CYP2C19 phenotypes. Tests were linear trend tests.

Results: Sertraline concentration/dose ratios were significantly different between CY2C19 phenotypes (p = 0.0003) and gene-drug interaction categories from the combinatorial pharmacogenomic test (p = 5.8e-06). Sertraline blood levels were 71% lower when the combinatorial pharmacogenomic test predicted significant GDI with increased metabolism compared to no GDI (p = 0.001). Similarly, sertraline blood levels were 134% higher when the combinatorial pharmacogenomic test predicted significant GDI with decreased metabolism compared to no GDI (p = 2.7x10-5). In a multivariate analysis that included CYP2C19 and the combinatorial pharmacogenomic algorithm, only the combinatorial pharmacogenomic algorithm remained significant (p = 3.8x10-5).

Conclusions: Combinatorial pharmacogenomic testing was a significant predictor of sertraline blood levels for patients within the GUIDED trial, accounting for all variance predicted by CYP2C19 alone and adding significant, independent information. This suggests that the combinatorial pharmacogenomic test may provide more clinically relevant information to inform medication decisions regarding sertraline compared to phenotypes based on CYP2C19 alone.

Keywords: Pharmacogenomics, Sertraline, Major Depressive Disorder (MDD)

Disclosure: Janssen, Otsuka: Contracted Research (Self)

Sage Therapeutics: Advisory Board (Self)

Xenon Pharmaceuticals: Consultant (Self)

American Psychiatric Press, Wolters Kluwer, University of Massachusetts Medical School: Royalties (Self)

P373. Metabolic Profile of Lumateperone (ITI-007) Monotherapy in Bipolar Depression: A Post Hoc Analysis of 2 Randomized, Placebo-Controlled Trials

Robert Davis*, Suresh Durgam, Richard Chen, Susan Kozauer, Sharon Mates, Christoph Correll

Intra-Cellular Therapies, Inc., San Diego, California, United States

Background: Treatments for bipolar depression are limited and can be associated with a spectrum of undesirable side effects, including metabolic disturbances. Lumateperone (lumateperone tosylate, ITI-007), a mechanistically novel antipsychotic that simultaneously modulates serotonin, dopamine, and glutamate neurotransmission, is FDA-approved for the treatment of schizophrenia and is being investigated in bipolar depression. This novel mechanism of action could confer improved tolerability compared with available treatment options for patients with bipolar I or bipolar II disorder experiencing a major depressive episode (MDE, bipolar depression).

Lumateperone 42 mg monotherapy was evaluated in 2 Phase 3 randomized, double-blind, placebo-controlled, 6-week trials (Study 401 [NCT02600494], Study 404 [NCT03249376]) in patients with bipolar depression. A pooled safety analysis of these studies assessed the metabolic profile of lumateperone 42 mg monotherapy in the treatment of bipolar depression.

Methods: The 2 studies investigated lumateperone 42 mg treatment in patients (18–75 years) with a confirmed diagnosis of bipolar I or bipolar II disorder experiencing an MDE (Montgomery-Åsberg Depression Rating Scale [MADRS] Total score ≥ 20 and Clinical Global Impression Scale-Bipolar Version-Severity [CGI-BP-S] score ≥ 4). Lumateperone 42 mg was administered orally once-daily for 6 weeks. Safety data were pooled from studies 401 and 404 including adverse events (AEs) that were spontaneously reported or discovered during physical examination, laboratory parameters, and vital signs.

Results: The safety population comprised 746 patients (lumateperone, 372; placebo, 374). Compared with placebo, mean changes from baseline to the last on-treatment value in weight were similar for lumateperone 42 mg (+0.06 kg) and for placebo (+0.19 kg). There was no potentially clinically significant weight gain (≥7% increase) during the treatment period for lumateperone 42 mg (lumateperone, 0%; placebo, 1.4%). Mean increase from baseline in body mass index for lumateperone (+0.02 kg/m2) was similar to placebo (+0.07 kg/m2). Changes in mean waist circumference were not clinically significant between groups (lumateperone, 0.18 cm; placebo, 0.03 cm).

Mean change from baseline to the last on-treatment measure in cholesterol were similar between treatment groups for total cholesterol (lumateperone, −0.6 mg/dL; placebo, −1.1 mg/dL), LDL-cholesterol (lumateperone, −0.7 mg/dL; placebo, −0.6 mg/dL), and HDL-cholesterol (lumateperone, +0.4 mg/dL; placebo, 0.0 mg/dL). Mean changes from baseline to the last on-treatment measure were similar between groups for triglycerides (lumateperone, −1.4 mg/dL; placebo, −4.0 mg/dL) and glucose (lumateperone, +0.1 mg/dL; placebo, 0.0 mg/dL).

Conclusions: In patients with bipolar I or bipolar II disorder with an MDE, lumateperone 42 mg monotherapy was generally well-tolerated and had a metabolic profile that was similar to placebo. These results suggest indirectly that lumateperone may have a more benign metabolic profile than currently approved treatments for bipolar depression.

Keywords: Bipolar Depression, Mood Disorders, Bipolar I And II Disorder, Antipsychotic Treatment, Psychotic Disorders

Disclosure: IntraCellular Therapies, Inc.: Employee, Stock/Equity (Self)

P374. Preliminary Results for ECT Amplitude-Determined Seizure Titration to Maximize Clinical and Cognitive Outcomes

Christopher Abbott*, Zhi-De Deng, Miklos Argyelan, Sephira Ryman, Abhishek Datta, Shawn McClintock

University of New Mexico, Albuquerque, New Mexico, United States

Background: Electroconvulsive therapy (ECT) stimulation parameter selection reflects a balance between antidepressant efficacy and cognitive adverse effects. ECT stimulation parameters associated with more antidepressant efficacy (non-focal electrode placement, longer pulse width) are associated with increased risk of cognitive adverse effects. Amplitude is currently fixed at 800 or 900 milliamperes (mA) in standard clinical practice with no clinical or scientific basis. Amplitude determines the intensity of the spatial distribution of the electric field (E-field). With a fixed extracranial amplitude, the ECT “dose” as represented by the E-field is highly variable due to anatomic differences in skin, skull, fluid, and brain tissue. This anatomic variability is prominent in older (age 50+) patients with depression and can compromise both antidepressant efficacy (insufficient stimulation of mood-related circuitry) and safety (inducing cognitive impairment due to excessive stimulation of cognitive related circuitry). Amplitude titration can reduce the variability related to fixed amplitude dosing and optimize clinical and cognitive outcomes. Here, we performed amplitude-determined seizure titration during the first treatment with subsequent treatments at fixed amplitude (800 mA). We assessed the relationship between amplitude-determined seizure titration and antidepressant and cognitive outcomes with fixed amplitude ECT.

Methods: Subjects with major depressive disorder or bipolar II diagnoses and age between 50 and 80 years received antidepressant ratings (Inventory of Depressive Symptomatology – Clinician Rated (IDS-C)) and neuropsychological assessments pre-, mid-, and post-ECT. For cognitive outcomes, we focused on the Delis Kaplan Executive Function Verbal Fluency Test (Letter Fluency Scaled Score; DKVFLFSS), a frontal-temporal cognitive task sensitive to cognitive impairment with right unilateral electrode placement (RUL) and amplitude strength. The first treatment determined amplitude-determined seizure threshold with RUL. Amplitude titration requires an interface (Soterix Medical 4x1 High Definition – ECT Multi-channel Stimulation Interface, Investigational Device Exemption #G200123) to attenuate the pulse amplitude from an FDA-cleared ECT device. Subsequent treatments were completed with RUL at 800 mA amplitude. Pulse width (1.0 milliseconds), pulse train duration (8 seconds), and frequency (20 hertz) were fixed during amplitude titration and subsequent treatments. Subjects had to demonstrate antidepressant response (defined as > 25% reduction in the IDS-C) to remain in the experimental protocol. If subjects did not demonstrate sufficient antidepressant response, subjects received bitemporal electrode placement (BT) for the remainder of the ECT series. For these preliminary results, we used descriptive and non-parametric statistics (spearman rank correlation coefficient, Wilcoxon rank-sum test) to assess the relationship between amplitude determined seizure threshold and antidepressant and cognitive results with RUL.

Results: Eight subjects (64.6 years +/- 10.5, 3 females) completed the study protocol to date. Amplitude-determined seizure thresholds demonstrated a wide range (361.6 mA +/- 160.1, range: 189 – 686 mA). Sex differences were not evident with amplitude determined seizure threshold (z = 1.0, p = 0.30). The relationship between amplitude-determined seizure threshold and antidepressant response (percent change in IDS-C) showed an inverse relationship (rho = -0.71, p = 0.04). Females had improved antidepressant response relative to males (z = -2.24, p = 0.03). The relationship between amplitude-determined seizure threshold and cognitive outcome (difference in DKVFLFSS) was not significant (rho = -0.49, p = 0.21). Sex differences were not evident with cognitive outcomes (z = -1.81, p = 0.07).

Conclusions: Our data demonstrated a 3.5x range of amplitude-determined seizure thresholds providing early support for individualized and empirically determined amplitudes. The inverse relationship between amplitude-determined seizure threshold suggested that lower amplitudes for seizure titration were consistent with subsequent antidepressant response with 800 mA. While amplitude titration will standardize the ECT dose across individuals with anatomic differences, the RUL amplitude necessary for seizure initiation will be insufficient to induce hippocampal neuroplasticity and antidepressant response. Analogous to the “six-times seizure threshold” multiplier for RUL ECT, amplitude-determined seizure threshold and the individualized amplitude sufficient for antidepressant response will require a multiplier that will bridge amplitude titration to the hippocampal “neuroplasticity threshold”, which is defined as E-field sufficient for neuroplasticity. The implications of this relationship suggest that individuals with a higher amplitude-determined seizure threshold may need higher amplitudes with RUL ( > 800 mA) or BT electrode placement to achieve an adequate ECT dose. Our goal is to further delineate the relationships between amplitude titration, electric field strength, and hippocampal neuroplasticity to individualize ECT-amplitude and maximize both clinical and cognitive outcomes.

Keywords: Electroconvulsive Therapy, Major Depressive Disorder (MDD), Cognition

Disclosure: Nothing to disclose.

P375. Plasma Cell-Free DNA Methylomics of Bipolar Disorder With and Without Rapid Cycling

Marin Veldic*, Ada Man-Choi Ho, Stacey Winham, Bryan McCauley, Marija Kundakovic, Keith Robertson, Zhifu Sun, Tamas Ordog, Lauren Webb, Mark Frye

Mayo Clinic, Rochester, Minnesota, United States

Background: Rapid cycling (RC) burdens bipolar disorder (BD) patients further by causing more severe disability and increased suicidality. Because diagnosing RC can be challenging, RC patients are at risk of rapid decline due to delayed suitable treatment. Circulating cell-free DNA (cfDNA) present in plasma, urine, cerebrospinal fluid, and other bodily fluids are short DNA fragments believed to be derived from cells undergoing apoptosis and necrosis and, possibly, released by active secretion thus allowing cfDNA to become potential biomarker of various conditions and diseases. Here, we aimed to identify the differences in the circulating cfDNA methylome between BD patients with and without RC. The cfDNA methylome could potentially be developed as a diagnostic test for BD RC.

Methods: This study included 93 (46 RC and 47 non-RC) participants enrolled in the Mayo Clinic Bipolar Disorder Biobank. The biobank was approved by the Mayo Clinic Institutional Review Board. Clinical phenotypes were confirmed by the Structured Clinical Interview for DSM-IV. About 25 ng of cfDNA was used for bisulfite conversion and methylome microarray analysis performed at the University of Minnesota Genomics Center in a single batch. Genome-wide methylomic profiling was performed on the 850K Infinium MethylationEPIC BeadChip platform (Illumina Inc., San Diego, CA, USA).

Principal component analysis (PCA) on the top 2000 most variable CpG probes considering all samples was conducted to assess global differences in methylome. Levels of cfDNA methylation were compared between RC groups using a linear model adjusted for age and sex. Association between the clusters and clinical factors were tested by chi-square and Fisher’s exact tests for categorical variables and t-tests for continuous variables.

We used the cell-type methylomic deconvolution algorithm to estimate the cell types of origin in each subject’s plasma cfDNA sample. Differentially methylated positions (DMPs; methylation status at individual sites) were identified by the R Bioconductor package limma. Differentially methylated regions (DMRs; methylation status across a genomic region) were identified by the R Bioconductor package DMRcate. Gene set enrichment analysis to determine if methylation levels of any gene sets were significantly associated with rapid cycling was performed using the missMethyl Bioconductor R package.

Results: Rapid cyclers and non-rapid cyclers were not significantly different in terms of age, sex, substance abuse and dependence history, and the use of lithium, mood stabilizers, and antidepressants. A significantly higher percentage of subjects were on antipsychotics in the rapid cycling group than the non-rapid cycling group (65.2% vs 40.4%).

PCA suggested differences in methylation profiles between RC groups (p = 0.039) although no significant differentially methylated probes (DMPs; q > 0.15) were found. The top four CpG sites which differed between groups at p < 1E-05 were located in CGGPB1 which encodes for CGG triplet repeat-binding protein 1, a nuclear protein that selectively binds to unmethylated CGG trinucleotide repeats; PEX10 which encodes peroxisomal biogenesis factor 10, a ubiquitously expressed peroxisomal matrix protein; NR0B2 which encodes nuclear receptor subfamily 0 group B member 2, an orphan nuclear receptor that interacts with receptors of estrogen, retinol, bile acid, and thyroid hormone to suppress the transcriptional activity of these nuclear receptors as well as with peroxisome proliferator-activated receptor α and γ; and TP53I11 (tumor protein P53-inducible protein 11), a target of TP53 with important role in conserving stability by preventing genome mutation.

Gene set enrichment analysis on top DMPs (p < 0.05) showed significant enrichment of gene sets related to nervous system tissues, such as neurons, synapse, and glutamate neurotransmission. Other top notable gene sets were related to parathyroid regulation and calcium signaling.

Between rapid cyclers and non-rapid cyclers, no significant differences in estimated cfDNA cell/tissue types of origin were found (p > Bonferroni-adjusted α = 0.05/26 = 0.001923), hence no adjustment in tissue/cell type origin distribution on the methylome analysis was conducted.

Conclusions: In this study, we used a microarray method to detect plasma cfDNA methylation levels to examine the cfDNA methylomic differences that were associated with rapid cycling in BD. We found global differences in methylation profiles between BD rapid cyclers and non-rapid cyclers, four CpG sites with differential methylation levels between BD rapid cyclers and non-rapid cyclers at p < 1E-05 (not genome-wide significant), and significant enrichment in pathways related to neurons and synaptic functions among the top CpG sites that differed between the groups. To our knowledge, this is the first investigation of cfDNA methylomics as potential biomarkers for BD rapid cycling, thereby marking an example of cfDNA application in psychiatric diagnosis and providing insights into amelioration of rapid mood cycling in BD.

Keywords: Cell-free DNA, Epigenetics, Bipolar Disorder, Rapid Cycling, Biomarker

Disclosure: Nothing to disclose.

P376. Examining White Matter Microstructure in Suicide Attempt and Treatment-Resistant Depression Using Tract-Based Spatial Statistics and Free Water Imaging

Katie Vandeloo, Sylvain Bouix, Patricia Burhunduli, Pierre Blier, Jennifer Phillips*

University of Ottawa Institute of Mental Health Research, Ottawa, Canada

Background: Clinical prediction of suicide attempt is limited, and the neurobiological factors distinguishing suicide ideators from suicide attempters are understudied. Preliminary investigations have indicated the use of spatially and temporally specific neuroimaging modalities to illustrate circuit-level dysfunction in psychiatric disease, including depression and suicide. Diffusion Tensor Imaging (DTI) provides the opportunity to identify white matter microstructural correlates associated with suicide attempt history. The source of white matter alterations may be further elucidated using free water imaging correction to isolate signal specific to the fibre tract and quantify the fractional volume of the free water compartment.

Methods: DTI data were acquired from N = 36 male and female patients with treatment-resistant major depressive disorder (n = 20 suicide ideators, n = 16 suicide attempters, ages 18-65 years). Tract-based spatial statistics (TBSS) was performed in FMRIB Software Library (FSL) using an unpaired two-samples t-test including age and sex as covariates. Free water imaging correction was applied through estimation of a constrained bi-tensor model via an in house MatLab-based script developed at Harvard University. Between-group differences of suicide ideators versus attempters were identified at a family-wise error (FWE) corrected significance threshold of p ≤ 0.05. Subsequent exploratory analyses were performed at an uncorrected significance threshold of p ≤ 0.01.

Results: Suicide ideator and attempter groups were well matched with no significant between-group differences in age, sex, handedness, depression severity, length of current major depressive episode, number of previous depressive episodes, or age of onset of major depressive disorder (all p > 0.05). TBSS revealed significantly elevated mean and axial diffusivity in suicide attempters relative to suicide ideators, as well as elevated extracellular free water in several fronto-thalamo-limbic tracts (FWE p ≤ 0.05). Exploratory analyses revealed reduced fractional anisotropy and elevated radial diffusivity in focal white matter areas (uncorrected p ≤ 0.01). Alterations in several overlapping tracts across diffusion metrics included the inferior and superior longitudinal fasciculi, uncinate fasciculus, inferior fronto-occipital fasciculus, anterior thalamic radiation, anterior limb of the internal capsule, and cingulum bundle adjacent to the hippocampus. Free water correction appeared to increase detection of fractional anisotropy changes and suppress spurious differences in axial and radial diffusivity.

Conclusions: In this preliminary investigation, the identification of significantly altered diffusion metrics in suicide attempters compared to suicide ideators suggests white matter pathology in treatment-resistant depression and suicide attempt. The effect of free water correction on all diffusion metrics and the elevation of free water itself provide evidence toward the source of anisotropic changes. To our knowledge, these results provide the first evidence of extracellular free water alterations associated with history of suicide attempt. Future investigations are recommended to explore the combined impact of these measures in suicide and depression.

Keywords: Diffusion Tensor Imaging (DTI), Suicide Attempt, Treatment-Resistant Depression, Free Water Imaging

Disclosure: Nothing to disclose.

P377. Depression Epigenome Wide Association Study Meta-Analysis Reveals Differential Methylation Positions and Regions Annotated to TNNT3

Qingqin Li*, Randall Morrison, Gustavo Turecki, Wayne Drevets

Johnson and Johnson Pharmaceutical, Titusville, New Jersey, United States

Background: Epigenetic mechanism has been hypothesized to play a role in MDD etiology. In this study, we performed meta-analysis between two case-control MDD cohorts to identify differentially methylated positions (DMPs) and differentially methylated regions (DMRs).

Methods: Whole blood samples were collected from two cohorts and DNA methylation was measured using Illumina MethylationEPIC array at 850 000 CpG sites throughout the genome. For the first cohort, the controls were self-reported not to have MDD collected by BioIVT (N = 32) and the MDD cases (N = 191) were drawn from OBSERVEMDD0001 study (NCT02489305), where a patient must have met DSM-V criteria for nonpsychotic, recurrent MDD within the past 24 months (ie, the start of the most recent major depressive episode (MDE) must be ≤ 24 months before screening); have a Montgomery Asberg Depression Rating Scale (MADRS) total score ≤14 at screening and baseline visits; have evidence of recent response (within the past 3 months) to an oral antidepressant treatment regimen (taken at an optimal dosage and for an adequate duration); and be currently taking and responding to an oral antidepressant treatment regimen. The samples from the participants with MDD could have been obtained from either a baseline visit or a follow up visit. For the second cohort, the MDD cases (N = 359) were drawn from the Molecular Biomarkers of Antidepressant Response study, where a patient must have had a diagnosis of current MDE, as per the SCID-I and HAMD-21 ≥ 20, while the controls (N = 68) were recruited through advertisement. Two or more samples from the same patient could have been collected. EWAS association analysis was conducted using limma while correcting for age, gender, estimated cell composition, five surrogate variables aiming to capture systematic technical variations (sample relatedness were corrected for using duplicateCorrelation) for each cohort. Inflation of test statistics was also corrected using BACON. This was followed by a meta-analysis between the 2 cohorts. DMPs with association p-values less than 6x10-8 were considered as study wide significant. Methylglm based pathway enrichment analysis was performed using DMPs with association p-value less than 0.0001. Lastly, comb-p analysis was performed to identify DMRs in the genome consisting of ≥ 3 probes. For DMR analysis, a Sidak-corrected p-value less than 0.05 was considered as study wide significant.

Results: Multiple cytosine-phosphate-guanine (CpG) sites annotated to TNNT3 were associated with MDD status reaching study wide significance, including cg08337959 (p = 2.3 x 10-11). Among DMPs with association p-values less than 0.0001, pathways from Reactome such as ras activation upon Ca2+ influx through NMDA receptor (p = 0.0001, p-adjusted = 0.05) and long-term potentiation (p = 0.0002, p-adjusted = 0.05) were enriched in the depressed samples. A total of 127 DMRs with Sidak-corrected p-value < 0.05 were identified from the meta-analysis, including DMRs annotated to TNNT3 (chr11: 1,948,933 to 1,949,130 [6 probes], corrected p = 4.32 x 10-41), NRXN1 (corrected p = 1.19 x 10-11), IL17RA (corrected p = 9.31 x 10-8), and neuropeptide FF receptor 2 (NPFFR2) (corrected p = 8.19 x 10-7).

Conclusions: Using 2 cohorts of depression case control samples, we identified DMPs and DMRs associated with depression case status. Future meta-analysis with other MDD case control cohorts in the scientific community under the leadership of Psychiatric Genomic Consortium will further elucidate the epigenetic mechanisms associated with depression.

Keywords: EWAS, Depression, DNA Methylation

Disclosure: Johnson and Johnson: Employee (Self)

P379. Kappa-Opioid Receptors (KORs) on Microglia: Expression and Regulation of Pro-Inflammatory Signaling

Galen Missig*, Niyati Mehta, Emma Fritsch, Miles Damon, Erica Jarrell, Andrew Bartlett, Robert Fenster, Kenneth McCullough, William Carlezon

McLean Hospital, Harvard Medical School, Belmont, Massachusetts, United States

Background: There is growing evidence that neuropeptide receptors expressed on microglia have important roles in the regulation of microglia function. Previous studies suggest that Oprk1, the mRNA that encodes kappa-opioid receptors (KORs), is expressed in microglia, and that activation of KOR receptors on microglia in vitro suppresses pro-inflammatory signaling. Beyond this small number of studies, however, the potential roles for microglia KORs in inflammatory and stress-related conditions have not been thoroughly investigated. Here, we examined KOR expression and function within nucleus accumbens (NAc) cell subtypes under baseline conditions and in response to immune system activation.

Methods: We used single-cell RNA sequencing (scRNAseq) of NAc in male C57Bl/6J mice to quantify Oprk1 expression in neurons and microglia. To examine if KORs play a functional role in regulation of inflammatory signaling, we administered the long-acting and selective KOR antagonist JDTic (30 mg/kg, IP) 24 hours prior to lipopolysaccharide ([LPS], 0.5 mg/kg, IP), which produces robust but transient immune activation. In Experiment 1, three hours after LPS, we isolated microglia for rt-qPCR analysis using magnetic cell sorting to separate NAc homogenates into microglia/brain macrophage (CD11b+) and non-microglia (CD11b-) fractions. We then extracted RNA and performed rt-qPCR to determine changes in proinflammatory gene expression. Simultaneously, we collected plasma for systemic cytokine analysis. In Experiment 2, we implanted mice with intraperitoneal wireless telemetry devices (TA-F10, DSI) to enable continuous measurement of core body temperature and locomotor activity. After one week of recovery, we collected 3 days of baseline data before administering JDTic (30 mg/kg, IP) followed 24 hr later by LPS (0.5 mg/kg, IP). After 24 hr of data collection, we perfused the mice for immunohistochemistry analysis of microglia markers. Group differences were examined using two-way ANOVAs and Sidak’s multiple comparisons tests.

Results: In our NAc scRNAseq dataset, we found expression of Oprk1 in both neurons and microglia. These findings are consistent with previous reports, although our data suggest that the mRNA is expressed in some but not all NAc microglia. In Experiment 1, we found that LPS significantly downregulated Oprk1 expression in microglia (p < 0.05). In microglia isolation experiments, LPS substantially upregulated the proinflammatory cytokines Il-1ß, Tnf, and Il-6, in both CD11B + (p’s < 0.01) and CD11B- fractions (p’s < 0.01), although expression levels were substantially higher in the CD11B + fraction. Pretreatment with KOR antagonist JDTic significantly enhanced LPS-induced upregulation of inflammatory cytokines Il-1ß (p < 0.05), Tnf (p < 0.05), and Il-6 (p = 0.05) in the CD11B + fraction and Tnf (p < 0.05), Il-6 (p < 0.01), but not Il-1ß (p > 0.05) in the CD11B- fraction (n’s = 6 per group). JDTic also affected LPS-induced peripheral inflammatory responses, producing enhanced levels of Il-1ß and IL-6 in blood (p’s < 0.01). In Experiment 2, LPS suppressed locomotor activity (p < 0.01) and produced hyperthermia (p < 0.05) for several hours following administration (n’s = 4-5 per group). While JDTic pretreatment enhanced LPS-induced hyperthermia, it did not affect the altered levels of locomotor activity.

Conclusions: These studies suggests that KORs play an important role in the regulation of inflammatory signaling in the brain. We demonstrate that KOR mRNA is expressed in microglia and that its expression is regulated by LPS-induced immune activation. We also demonstrate that KOR signaling in microglia appears functional and regulates inflammation, as administration of a KOR antagonist amplifies LPS-induced central inflammatory processes (upregulation of proinflammatory genes in microglia), peripheral inflammatory processes (elevation of peripheral cytokines), and physiological responses (hyperthermia). Further work is needed to more thoroughly characterize the ways in which KORs expressed on microglia versus other immune cells contribute to regulation of these endpoints. Likewise, future studies are needed to determine if there are sex differences in these effects. Regardless, these studies may have important implications for the use of KOR antagonists in treatment of depressive disorders, which have been previously associated with elevated pro-inflammatory signaling.

Keywords: Kappa Opioid Receptor, Immune Responses, Depression and Anxiety, Microglia

Disclosure: Nothing to disclose.

P380. Proliferation of Putative GABA/Glutamate Co-Releasing Terminals in the Primate Habenula

Lupita Rios, Chunfeng Tan, Alaa Hajeissa, Vishal Narla, Kelly Gleason, Carol Tamminga, Steven Shabel*

University of Texas Southwestern Medical Center, Dallas, Texas, United States

Background: The lateral habenula (LHb) responds to aversive stimuli, and its hyperactivity is hypothesized to contribute to depression. Most of the central nervous system uses a balance of excitatory and inhibitory transmission from separate inputs to control neural activity. However, multiple inputs to the lateral habenula co-release GABA with glutamate in rodents; the balance of GABA and glutamate at these synapses may regulate LHb responses to aversive stimuli and mood. Here, we investigated whether the magnitude and topography of co-release of GABA and glutamate in the LHb is conserved in primates.

Methods: We performed immunohistochemistry on brain slices for GAD and Vglut2 (N = 34 slices, 6 mice; N = 23 slices, 5 monkeys; N = 11 slices, 6 humans) and VGAT and Vglut2 (N = 34 slices, 6 mice; N = 23 slices, 5 monkeys; N = 8 slices, 4 humans) at the level of the habenula and quantified the amount and topography of GAD/Vglut2 and VGAT/Vglut2 co-labeling within tiled confocal images (63X) using custom Matlab code. ANOVA and Student’s t-tests were used to determine statistical significance. Both sexes were included.

Results: We found increased GAD/Vglut2 and VGAT/Vglut2 co-labeling within the LHb compared to the adjacent thalamus in all species (all P < .0001). We also found increased GAD/Vglut2 and VGAT/Vglut2 co-labeling in the monkey and human LHb compared to the mouse LHb (P < .0001 and P < .005, respectively), and increased GAD/Vglut2 co-labeling in the human LHb compared to the monkey LHb (P < .05). The weighted center-of-mass of GAD/Vglut2 co-labeling was shifted dorsally in the LHb of monkeys and humans compared to mice (both P < .002).

Conclusions: Our data indicate substantially increased co-labeling of GAD (the synthesizing enzyme for GABA) and VGLUT2 (vesicular glutamate transporter), as well as VGAT (vesicular GABA transporter) and VGLUT2, in synaptic terminals in the monkey and human LHb, consistent with increased co-release of GABA and glutamate from individual terminals onto primate LHb neurons. We also found an expanded topography of co-release in the primate LHb, perhaps partly due to expansion of the LHb in primates. Thus, co-release of GABA with glutamate may be a mechanism for regulation of LHb activity and mood that proliferated during primate evolution.

Keywords: Neurotransmitter Co-Release, Habenula, Monkey

Disclosure: Nothing to disclose.

P381. Base Excision Repair Mechanism (BER) as a Potential Target for Treatment of Bipolar Disorder: A Case-Control Candidate Gene Study

Aysegul Ozerdem*, Marin Veldic, Balwinder Singh, Deniz Ceylan, Mark Frye, Thomas Schulze, Joanna Biernacka, Stacey Winham

Mayo Clinic, Rochester, Minnesota, United States

Background: Background:

Bipolar disorder (BD) is associated with early aging, increased mortality and morbidity due to various medical conditions which are known to be associated with oxidatively generated DNA damage. Recent evidence shows increased cancer risk in BD, particularly breast cancer in women, and lithium may have a potential protective effect on cancer. BD presents increased levels of oxidatively induced DNA damage. Base excision repair (BER) is the major repair mechanism of oxidative DNA damage. It is a stepwise process operated by multiple enzymes. We have previously shown increased protein and down regulated gene expression levels of genes encoding for BER enzymes in peripheral blood samples of BD patients compared to controls. Genes encoding BER enzymes were either hypomethylated or hyper methylated in post-mortem brain tissue samples of BD patients in comparison to controls. In this study we aimed to explore the association of 24 genes encoding for BER enzymes with BD and with lithium response. We hypothesized that genes encoding for BER enzymes were going to show significant association to BD and lithium response.

Methods: The previously published GWAS summary statistics of the Psychiatric Genomics Consortium (PGC)-Bipolar Disorder, including patients with BD (n = 20,352) and controls (n = 31,358), were used to perform gene-level analysis of candidate BER genes using the MAGMA approach implemented in the GWAS functional mapping and annotation platform FUMA. The genes APEX1, FEN1, LIG1, LIG3, MBD4, MUTYH, MPG, OGG1, NLTH1, NEIL1, NEIL2, NEIL3, PARP1, PNKP, PCNA, POLB, POLD1, POLE, POLG, SMUG1, TDG, UNG1, UNG2, and XRCC1, which encode for their corresponding BER enzymes, were included in the analysis.

Likewise, previously published GWAS summary statistics of 2500 patients with BD from the International Consortium on Lithium Genetics (ConLiGen) were used to perform gene level analysis for the association between lithium response and BER genes. Lithium response was analyzed as binary variable based on a score ≥7 on Alda scale after subtracting B subscale scores from A subscale scores.

Results: The gene encoding for the BER enzyme FEN1 met genome-wide significance criteria for association with BD (p = 4.5E-09), whereas genes encoding for MBD4 (p = 0.0063), TDG (p = 0.0073), MUTYH (p = 0.042), and PARP1 (p = 0.043) showed nominally statistically significant association to BD. PARP1 was the only gene that showed nominally statistically significant (p = 0.011) association with lithium response.

Conclusions: Our findings provide further evidence for the involvement of the BER mechanism in the pathogenesis of BD and response to lithium. The genes showing significant association to BD function at different steps of the BER pathway, suggesting a large-scale operational challenge in the DNA repair mechanism in BD. We do not yet know whether the altered DNA repair mechanism is the primary source or result of increased oxidative DNA damage in BD.

FEN1 is known to have a significant role in maintaining integrity of the mitochondrial DNA. MBD4, TDG and MUTYH are also known to be involved in mitochondrial DNA repair. Present data allows BD to be conceptualized as a mitochondrial disease. Recent research is exploring significance of FEN1 inhibitors in cancer treatment. PARP-1 is a key enzyme in regulating the balance between DNA repair and cell death in the case of severe DNA damage. Lithium was shown to reduce PARP-1 activity in response to oxidative stress in HeLa cells. As a non- competitive inhibitor of GSK-3, lithium induces apoptosis, and suppresses carcinoid cancer cell growth in vitro via increasing the PARP1 cleavage. Both PARP1 and lithium are active homeostatic regulators, meaning their effects are most pronounced in the presence of pathology. The interaction between lithium and PARP1 may be one of the mechanisms enabling lithium’s mood stabilizing effect. Taken together, the findings point at a future direction where BER mechanism can be explored for understanding the pathogenesis of BD and as a target for novel treatment options of illness. Data and experience from the cancer field can contribute significantly to our understanding of BER enzymes as novel targets for treatment of BD.

Keywords: Bipolar Disorder, Oxidative DNA Damage, Base Excision DNA Repair, Lithium, Gene Level Analysis

Disclosure: Nothing to disclose.

P382. Psychedelics for the Treatment of Mental Disorders: A Systematic Review and Network Meta-Analysis

Isis Lunsky, Gilmar Gutierrez, Anees Bahji, Gustavo Vazquez*

Queen’s University, Kingston, Canada

Background: Psychedelics, like MDMA, LSD, ayahuasca, and psilocybin, may have antidepressant and anxiolytic properties. Comparative performance of psychedelics for treating symptoms of mental disorders is unclear due to few head-to-head trials. We aimed to compare the efficacy and safety of psychedelics for depression, anxiety, and posttraumatic stress disorder symptoms in adults. Secondary outcome was dichotomized all-cause treatment discontinuation

Methods: Four major bibliographic databases (PubMed, MEDLINE, PsycINFO, and Embase) were searched for trials comparing psychedelic (with or without concomitant therapies) to February 2021. Randomized trials comparing psychedelics for mood, anxiety, or posttraumatic stress disorder symptoms in adults were included after blind review by three independent reviewers. We followed the PRISMA guidelines for abstracting data and applied the Cochrane risk of bias tool for evaluating the study-level risk of bias. Data abstraction was done by one reviewer and confirmed by two independent blind reviewers. Primary outcomes were scores on instruments for depression, anxiety, and posttraumatic stress disorder symptoms and treatment discontinuation due to adverse effects. Secondary outcomes were dichotomized all-cause treatment discontinuation. We pooled effect sizes using frequentist random-effects network meta-analysis models to generate summary rate ratios (RRs) and Cohen’s d standardized mean differences (SMDs). Negative Cohen’s d (SMDs) or RRs<1 indicate that the treatment reduced the parameter of interest relative to the control (e.g., signifying a beneficial effect for depression severity).

Results: The systematic search provided a total of 1368 citations, from these, we selected 67 studies for eligibility assessment (n = 562, 54% female) and chose 17 studies for full text review. None of the investigated psychedelics caused more dropouts or dropouts due to adverse events than placebo, indicating high tolerability of psychedelic-assisted therapy. Psilocybin (d = -2.71, 95% CI: -3.46, -1.96) and ayahuasca (d = -1.57; 95% CI: -2.90, -0.23) had large effect sizes for depressive symptoms, while MDMA (d = -0.95, 95% CI: -1.28, -0.62) showed efficacy for PTSD symptoms. Psilocybin also demonstrated a large anxiolytic effect (d = -1.88; 95% CI: -2.70, -1.06). In parallel, psilocybin, ayahuasca, and MDMA demonstrated large effect sizes for response and remission rates, ranging from RRs of 2.65 to 5.44. In head-to-head comparisons between psychedelics, psilocybin outperformed MDMA and LSD for depression symptoms. We downgraded the strength of evidence due to heterogeneity, publication bias, and imprecision in some outcomes.

Conclusions: While some psychedelics appear well-tolerated and demonstrate some efficacy for symptoms of depression, anxiety, and PTSD, the strength of evidence in our estimates was low to very low for most agents given the small sample sizes and few RCTs. A lack of consistent evidence precludes a definitive hierarchy of treatments and points to a need for additional, high-quality RCTs.

Keywords: Psychedelics, Depression and Anxiety, PTSD

Disclosure: Nothing to disclose.

P383. The Genetic Liability of Severe Mental Illness and Chronotype

Monica Federoff*, Michael McCarthy

UCSD School of Medicine, San Diego, California, United States

Background: Chronotype disruptions, often in the form of circadian misalignment, are known to be correlated among patients with bipolar disorder (BD), schizophrenia (SCZ) and other forms of severe mental illness. These circadian disturbances include misalignment in sleep and daily activity patterns. It remains unclear if genetic liability towards chronotype corresponds with an individual’s risk of developing a psychiatric disorder. Polygenic risk scores (PRS) are a well-established methodology to estimate the genetic liability associated with a particular disease or trait using SNP association derived from genome-wide association (GWA) data. There has been increasing evidence of shared genetic risk between forms of severe mental illness, including SCZ and BD, through the collective sum of common risk alleles, though little is known about the genetic degree of overlap with chronotype predisposition.

Methods: In this study we used genotype data derived from approximately 420,000 single nucleotide polymorphisms (SNP) of 415 subjects with BD I (with clinically defined levels of lithium responsiveness) derived from the Pharmacogenetics of Bipolar Disorder (PGBD) trial. PRS for BD and SCZ were calculated using summary statistics from the most recent PGC analyses. At the first study visit of the PGBD trial, 385 subjects completed the Basic Language Morningness scale (BALM), a validated, 13-item self-reported measure of chronotype (36, 37). Higher BALM score corresponds to a greater level of morningness. Chronotype and morningness were calculated from summary statistics of the UK Biobank. Data were examined at five thresholds for statistical significance (α < 0.01, 0.05, 0.1, 0.2 and 1.0). Fibroblast cell lines derived from skin biopsies of 59 PGBD study participants with informative clinical outcomes (N = 44 Li-R/15Li-NR) were transduced with the Per2-luc lentiviral reporter gene to assess circadian rhythms. BD patient fibroblast rhythms were recorded using ~1.2 x 106 cells in 35 mm plates over 5 days with a luminometer.

Results: The PRS using p < 0.01 showed significant overlap in PRS for BD and SCZ, significant overlap in PRS for chronotype and morningness, and trend level overlap between chronotype and BD at p = 0.06. At a PRS p < 0.05, there was a very strong correlation with morningness and chronotype, BD and SCZ, and no correlation between BD and chronotype or morningness. There was a significant negative correlation between SCHZ, chronotype and morningness. Unadjusted BALM scores demonstrated a modest but significant correlation with morningness, but no correlation with chronotype. By adjusting for age, morningness PRS explains slightly more variance for BALM than age alone (R2 = 0.12 AGE ONLY, 0.14 PRS P < 0.05, 0.15 PRS < 0.01). In cellular rhythm assays, PRS for morningness was nominally correlated with period (PRS p < 0.01 = 0.13 and PRS p < 0.05 = 0.16) but these were not statistically significant. Correlations were nominally higher than those for BD and SCZ but the difference was not significant. Similar results for phase r = 0.07, 0.13, 0.15, 0.16, 0.16 for each p-value respectively. In cells with BALM scores the absolute r values had insufficient power due to limited sample size.

Conclusions: Collectively, these data suggest there is some evidence of shared genetic liability towards the development of severe mental illness, specifically SCZ, with chronotype (dimensional) and morningness (categorical) at the most stringent p value <0.01). While not meeting threshold for statistical significance, cellular rhythms assays of BD I subjects demonstrated some evidence of correlation between PRS for morningness and different parameters of circadian rhythm (period, phase), demonstrating the translational utility of cellular models to provide informative data of chronotype and morningness in corresponding clinical subjects.

Keywords: Circadian Rhythm, Severe Mental Illness, Polygenetic Risk Score

Disclosure: Nothing to disclose.

P384. EEG Power Spectral Analysis: A Potential Mechanistic Strategy to Assess rTMS Neurophysiological Effects?

Camila Cosmo*, Amin Zandvakili, José Garcia Vivas Miranda, Noah Philip

Alpert Medical School, Brown University; Center for Neurorestoration and Neurotechnology, Providence VA Medical Center, Providence, Rhode Island, United States

Background: Treatment Resistant Depression (TRD) is associated with humanistic and economic burden, with an enormous impact on health, productivity, and social dynamics. For over a decade, repetitive Transcranial Magnetic Stimulation (rTMS) has demonstrated effectiveness in TRD. This technique has been widely studied, and different neurophysiological approaches have been used to investigate its effects on neural circuitry modulation. Nevertheless, the mechanism of action of rTMS and its effects over time still are not fully understood. Quantitative Electroencephalography (qEEG) power spectral analysis might function as a mechanistic strategy to clarify the neurophysiological effects of rTMS and to optimize future treatment protocols.

Methods: In this longitudinal pilot study, resting-EEG activity was measured in six subjects with TRD who received up to 30 sessions of rTMS (5Hz, 120%MT, 3,000 pulses/session, over the left dorsolateral prefrontal cortex). The EEG was recorded through 64 channels, during 10 minutes, with eyes closed, at baseline (T0), after 10 rTMS sessions (T1), after 20 sessions (T2), and immediately after the last stimulation treatment (T3). The main outcomes were differences in the FFT-based power spectral analysis over time as measured by qEEG using the EEGLAB/MATLAB software system (The Mathworks, Inc.).

Results: One-way repeated measures ANOVA showed a significant decrease in the absolute power in the beta band over the left dorsolateral prefrontal cortex (F (3, 15) = 3.58, p = 0.039), with effects observed at T1 and progressing over time. No other significant changes were observed in delta, theta, or alpha power following the stimulation sessions (p ≥ .05).

Conclusions: Our findings suggest that qEGG might be a feasible strategy to monitor rTMS-induced changes in cortical networks. Prior studies have shown an association between depressive symptoms and increased beta power in frontal regions. Our results demonstrated that rTMS elicited a reduction in beta power over time, starting as early as after the first ten sessions. Future studies might consider EEG acquisition during rTMS, a larger sample, and the correlation of qEEG findings with clinical outcomes to assess whether qEEG power spectral analysis might function as a rTMS biomarker for TRD.

Keywords: Quantitative Electroencephalography (qEEG), Repetitive Transcranial Magnetic Stimulation (rTMS), Major Depression Disorder, Neurophysiology, Non-Invasive Neuromodulation

Disclosure: Nothing to disclose.

P385. Exploring Relationships of GABA and Glutamate With Negative Valence Systems

Jessica Busler*, Katherine Coleman, Sarah Rose Slate, Eduardo Coello, Monica Foneska, Vicky Liao, Alexander Lin, Pamela Mahon

Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, United States

Background: Negative valence systems are defined by the NIMH Research Domain Criteria (RDoC) framework as systems responsible for responses to aversive situations or context, and includes constructs such as fear, anxiety and loss. Dysregulation of negative valence systems is a characteristic of mood disorders and is observed in other mental disorders, as evidenced by difficulties in affective processing and emotion regulation, with corresponding alterations in emotion regulation neurocircuitry. Dysregulation in GABAergic (primary inhibitory) and glutamatergic (primary excitatory) systems within this neurocircuitry has been implicated in mood and other disorders. However, the relationship of neurometabolic dysregulation to negative valence systems more generally is not well understood. We aimed to examine brain markers of GABAergic and glutamatergic function in a brain region involved in emotion regulation (dorsolateral prefrontal cortex (DLPFC)) and their relationship to function in negative valence systems, measured at the self-report and behavioral levels.

Methods: Twenty participants (14 women and 6 men) were recruited at Brigham and Women’s Hospital, including both healthy participants and participants with a mood disorder in order to enrich the sample for a range of function within negative valence systems. Participants were ages 35-61 (M = 46.50, SD = 8.50). Self-report negative affect summary score from NIH Toolbox was assessed, along with a behavioral measure using an affective go/no-go task with positive, neutral, and negative valenced stimuli. Attentional bias toward negative stimuli was measured by comparing number of commission and omission errors and reaction time to negative stimuli against responses to positive and neutral stimuli. MR spectroscopy, using STEAM at 7 Tesla (TE = 20ms, TM = 10ms, TR = 3000ms), was used to measure markers for GABA and glutamate in the DLPFC and LCModel was used for neurometabolite quantification. Spectroscopy results were filtered to exclude results with a CRLB > 20. We conducted separate correlation analyses of each neurometabolic marker with negative affect scores from NIH Toolbox and with measures of attentional bias from the affective go/no-go task.

Results: We observed a significant inverse correlation between DLPFC GABA and the negative affect summary score (r = -0.670, p = 0.009). For analyses involving negative attentional bias we observed that for the contrast comparing response time to negative and positive stimuli, DLPFC GABA was significantly inversely correlated with response time consistent with bias towards negative stimuli (r = -0.632, p = .027). Further, results showed that DLPFC GABA was significantly inversely correlated with omission errors for negative versus neutral stimuli, consistent with bias towards negative stimuli (r = -0.634, p = .027). We did not observe a significant association between DLPFC GABA and commission errors. No other significant results were observed in testing relationships of glutamate in the DLPFC with either negative affect scores or measures of negative affective bias.

Conclusions: These results suggest that GABAergic function, measured in the DLPFC, is inversely correlated with negative affect and negative attentional bias. Specifically, lower levels of GABA in the DLPFC were associated with higher negative affect scores and increased attentional bias toward negative stimuli. This finding is in line with studies implicating lower GABA in individuals with mood disorders. Accordingly, our findings suggest a role for DLPFC GABA in negative valence systems functioning more generally. Despite the promising nature of these findings, they are preliminary in nature and should be interpreted with caution given the small sample size. If confirmed, these findings have the potential to inform clinical care regarding the use of GABAergic medications to improve outcomes in disorders involving negative valence systems.

Keywords: Negative Valence System, MR Spectroscopy, Mood Disorder

Disclosure: Nothing to disclose.

P386. Baseline Intrinsic Functional Brain Connectomes Predict Treatment Outcome for Depression Comorbid With Obesity: A Report From the Engage Randomized Controlled Trial

Xue Zhang*, Patrick Stetz, Andrea N. Goldstein-Piekarski, Lan Xiao, Nan Lv, Lisa G. Rosas, Mark B. Snowden, Joshua M. Smyth, Trisha Suppes, Olusola Ajilore, Leanne M. Williams

Stanford University School of Medicine, Palo Alto, California, United States

Background: Typically, only 30-50% of patients with depression respond to antidepressant treatment, and lack of response is exacerbated with co-occurring obesity; only 17% of patients with depression and obesity respond to antidepressant treatment (1). Identifying predictors of treatment response can inform a precision medicine approach for treatment. Both depression and obesity have been characterized by altered intrinsic functional connectivity (FC) within and between large-scale neural networks (2, 3); however, it is still unclear whether those connectome signatures could be utilized to predict treatment response for depression comorbid with obesity.

Methods: We analyzed baseline functional MRI data of adult participants with depression and obesity who were randomized to receive an integrative collaborative care intervention (I-CARE, n = 59) that included problem-solving therapy with as-needed antidepressant medication for depression and a video-based behavioral weight loss treatment or usual care (n = 49) (4, 5). Participants in both treatment arms with ≥ 50% reduction of depression severity scores (20-item depression severity scale) at 6 months relative to baseline were defined as responders. Detailed steps for preprocessing and FC calculation could be found in previous publications (6, 7). In brief, concatenated residual time courses of three task fMRI data after removing the task-related activity were used to estimate baseline intrinsic functional connectome, using the Brainnetome atlas consisting of 246 cortical and subcortical regions of interest (ROI) labeled with Yeo’s 7 networks parcellation (8). ROI-to-ROI pairwise FCs (246 x 246) were evaluated and transformed into z-scores using Fisher’s z transformation for each participant. To identify predictive markers of treatment response at 6 months, we used a linear regression model with each pair of the baseline FC as the dependent variable and the response group (responder or non-responder) as the independent variable, with age, gender, and baseline depression severity as covariates. To evaluate the predictive power of the identified baseline FC markers from the linear regression model, we used logistic regression models with the response group as the dependent variable, and the identified baseline FC markers combined with the baseline covariates as independent variables and compared it with only including the baseline covariates as dependent variables. A 5-fold nested cross-validation was conducted to test the generalizability of each model. The confusion matrix was generated for the calculation of accuracy, sensitivity, and specificity. To further investigate whether the baseline FC markers were differentially associated with treatment response depending on treatment arm, we conducted a response (responder or non-responder) by treatment arm (I-CARE or usual care) two-way analysis of variance (ANOVA) model on the identified FC markers and focused on the interaction effect of response by treatment. To help understand the findings, exploratory analyses included comparing two sub-items of baseline depression symptoms (item 4: feeling tired or having little energy and item 5: poor appetite or overeating from the patient health questionnaire-9), which might be key factors of response for patients with depression and obesity, between the responder and non-responder groups using a two-sample t-test and examining their associations with identified baseline FC markers using Spearman’s rank correlation within each treatment arm.

All pairwise ROI-to-ROI analyses were corrected for multiple comparisons via the network-based statistic (NBS) at an edge level p < 0.001 and a component level p < 0.05 using 1000 permutations (9). Exploratory analyses were not corrected for multiple comparisons.

Results: I-CARE was more effective in improving mood and reducing weight (10), and the overall response rate of depression at 6 months was 32%. Responders were characterized by a unique functional connectome profile compared to non-responders: a significantly lower baseline FC within the somatomotor network (SMN), between the SMN and the default mode network (DMN), visual network, dorsal and ventral attention network, limbic network, and subcortical regions, and a significantly higher baseline FC between the SMN and frontal-parietal network. A combination of baseline FC markers and covariates predicted treatment response with high accuracy, sensitivity, and specificity (cross-validated 88%, 89%, and 86% respectively), baseline covariates alone did not accurately predict treatment outcome (cross-validated 50%, 53%, and 43% respectively), indicating the utility of FC markers. We did not observe differences between I-CARE and usual care groups on the FC predictors of response. Responders had a tendency toward a higher baseline energy level (p = 0.065); however, it was not correlated with identified baseline FC makers within each treatment arm, indicating that higher baseline energy and the unique functional connectome might be trait-like characteristics of responders.

Conclusions: Using data from a precision medicine biomarker trial, we found that baseline functional connectomes, especially the within and between SMN FCs, were predictive biomarkers of treatment response for depression comorbid with obesity, irrespective of treatment type. Our findings highlight the promise of baseline functional connectome for tailoring treatment choices for depression comorbid with obesity.

Keywords: Depression and Obesity, Neuroimaging Biomarkers, Clinical Trial

Disclosure: Nothing to disclose.

P387. Aberrant Functional Maturation of a Novel Cell-Type-Specific Brain Pathway Impacts Reward-Seeking Behaviors After Early-Life Stress

Matthew Birnie*, Annabel K. Short, Aidan L. Pham, Ashima Kundu, Christy A. Itoga, Xiangmin Xu, Stephen V. Mahler, Yuncai Chen, Tallie Z. Baram

University of California-Irvine, Irvine, California, United States

Background: The seeking of pleasure is a fundamental human behavior, executed by coordinated activity of the brain’s reward circuitry. Disrupted operation of this circuit is thought to underlie major emotional disorders including depression and drug-abuse, disorders commonly arising after early-life stresses. Yet, how early-life adversities (ELA) impact the functional maturation of reward circuitries to promote disease remains unclear. The nucleus accumbens (NAc) is a major component of the reward circuit and key structure mediating pleasure, motivation, and emotional processes. Multiple inputs converge onto the NAc to modulate reward-seeking behaviors, including the basolateral amygdala (BLA). The BLA mediates associate learning for both aversive and appetitive stimuli, and stimulation of glutamatergic projections from the BLA to NAc promotes appetitive behaviors. In this study, we employ viral-genetic technologies to identify a novel GABAergic projection that co-expresses the stress-related neuropeptide corticotropin-releasing hormone (CRH) and connects the basolateral amygdala (BLA) and nucleus accumbens (NAc). In the NAc, CRH + axon terminals modulate reward and motivational behaviors. Here, we identify the role of this CRH + BLA-NAc projection during reward in naïve and stress-experiencing mice.

Methods: To identify CRH + projections to the NAc, we utilized viral-genetic approaches to map these pathways using Cre-dependent viruses injected into CRH-IRES-Cre mice. To determine the function of the novel CRH + BLA-NAc projection we employ chemogenetic and optogenetic strategies in both control and early-life adversity experiencing mice. In these mice, we injected excitatory or inhibitory Cre-dependent DREADD (hM3Dq and hM4Di) and optogenetic (ChR2) carrying viruses into BLA, followed by medial NAc shell targeted microinjections of CNO or light activation. We tested the function of this pathway using three reward (sucrose preference, sex-cue approach, and palatable food tasks), and non-reward tasks (object location memory and open field).

Results: Viral genetic tracing paired with fluorescence in situ hybridization and immunostaining identified a novel GABAergic projection that co-expresses the stress-reactive neuropeptide CRH + projection from the BLA to the medial NAc shell. Excitation of this projection using chemo- and optogenetic tools reduced preference for sucrose, palatable food consumption, and sex-cue approach, but did not alter non-reward specific tasks (object location memory and open field). Compared with control mice, male mice that experienced ELA had reduced preference for sucrose, palatable food consumption and sex-cue approach. In adult ELA mice, chemogenetic inhibition of the CRH + BLA-NAc projection rescued all three reward behaviors.

Conclusions: We identify a novel GABAergic CRH + BLA-NAc projection and establish its role in mediating the effects of ELA on reward behaviors. These discoveries provide potential selective targets for prevention and intervention in the disruption of such behavior that accompanies several psychopathologies.

Funding: This work was supported by National Institutes of Health Grant Nos. MH73136 and MH096889 (to TZB) and the George E. Hewitt Foundation for Medical Research Postdoctoral Fellowship (to MTB).

Keywords: CRH, Reward, Adversity, Nucleus Accumbens, Amygdala

Disclosure: Nothing to disclose.

P388. Reduced Striatal Dopamine Binding to Rewards is Associated With Anhedonia Severity and Recent Stress

Rachel Phillips*, Erin C. Walsh, David Lalush, Jessica L. Kinard, Paul M. Cernasov, Lisalynn Kelley, David B. Campbell, Daniel G. Dillon, Diego A. Pizzagalli, David Izquierdo-Garcia, Nicole R. Zurcher, Chieh-En J. Tsen, Jacob M. Hooker, Moria Smoski, Gabriel S. Dichter

University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, United States

Background: Stress reduces goal-directed behavior and reward responsiveness and has been implicated as a significant contributor to the pathophysiology and manifestation of anhedonia. Anhedonia – deficits in motivation, effort, or pleasure – is a core feature of stress-related psychopathologies including major depression and posttraumatic stress disorder. A putative mechanism for the association between chronic stress and anhedonia is the downregulation of mesolimbic dopamine (DA) reward signaling. The purpose of this study was to use simultaneous PET-MR imaging to evaluate striatal dopaminergic functioning during reward processing in a transdiagnostic anhedonia sample, using the D2/D3 dopamine receptor antagonist [11C]raclopride. We hypothesized that, compared to a healthy control (HC) group, the anhedonic (ANH) group would demonstrate decreased striatal phasic DA release to rewards, indexed by the non-displaceable binding potential (BPND) of [11C]raclopride. Furthermore, we hypothesized that, within the ANH group, reduced phasic DA release in striatal regions would be associated with (a) greater anhedonia severity, and (b) elevated stress.

Methods: Adult participants (HC: n = 12, ANH: n = 24) underwent a simultaneous PET-MR scan session on a Siemens Biograph mMR scanner at the UNC Biomedical Research Imaging Center. Dynamic PET data were acquired for 70 minutes post-injection and reconstructed into 70 1-minute time frames. A bolus+infusion [11C]raclopride administration protocol was used to measure background dopaminergic tone and phasic dopaminergic release, via displacement of the tracer, in response to incentives. Participants completed a monetary incentive delay (MID) task, modified for use in PET-MR studies. The incentive task included a neutral run followed by two reward runs. During the two reward runs, concatenated into one reward block for PET analyses, money could be won; during the neutral run, money could not be won. Binding potential, the ratio of selectively bound ligand to nondisplaceable ligand in the tissue at equilibrium (BPND), was estimated from dynamic PET images for the neutral and reward states using the Simplified Reference Tissue Model (SRTM). BPND is negatively correlated with endogenous dopamine. In order to identify between-group differences in striatal BPND, a Z-score statistical map representing the difference between groups (ANH – CON) was created by comparing group-level voxel-wise BPND (reward – neutral) maps, thresholded at Z > 2.58. For clusters that showed group differences in striatal BPND in the reward relative to the neutral run, we examined associations between BPND values and anhedonia and stress measures within the ANH group. Anhedonia and stress measures were only collected in the ANH group (15 Females, 9 Males; aligned with 2:1 prevalence rates of major depression for females-to-males).

Results: A striatal cluster located in the left putamen demonstrated ANH > Control group differences for the contrast of (reward > neutral) BPND values, interpreted to mean decreased phasic DA release (increased BPND) in the reward relative to the neutral condition in the ANH group relative to the HC group. Within the ANH group, reduced phasic DA release to rewards in the left putamen was significantly correlated with recent stress, (R = .45, p = .027), assessed using the PTSD Symptom Checklist for DSM-5 (PCL-5). Recent stress was also assessed using the Perceived Stress Scale (PSS). Reduced phasic DA release to rewards in the left putamen was marginally associated with increased stress on the PSS, in the ANH group, demonstrating the same pattern as with stress measured by the PCL-5 (R = .40, p = .054). Moreover, there was a significant effect of recent stress (b = .002) on phasic DA release to rewards in the left putamen (F(1,22) = 5.92, p = .024, adjR2 = .17). Furthermore, within the ANH group, reduced phasic DA release to rewards in the left putamen was significantly correlated with anhedonia severity, (R = .44, p = .032), assessed using the anhedonia subscale of the Beck Depression Inventory (BDI-II) which comprised four items (loss of interest, loss of pleasure, loss of interest in sex and loss of energy). Finally, there was a significant effect of anhedonia severity (b = .013), assessed using the BDI-II, on phasic DA release to rewards in the left putamen (F(1,22) = 5.20, p = .033, adjR2 = .15). Anhedonia severity was also assessed using the Snaith-Hamilton Pleasure Scale (SHAPS); however, SHAPS scores were not significantly associated with reduced phasic DA release in the left putamen (p > .05).

Conclusions: In a transdiagnostic anhedonia sample, we found that recent stress and anhedonia severity are associated with reduced DA reward signaling in the left putamen. Relations between striatal DA release to reward and stress were evident across two stress measures (the PCL-5 and the PSS), but relations between striatal DA release to reward and anhedonia were evident only using the anhedonia subscale of the BDI-II and not the SHAPS. The anhedonia subscale of the BDI-II assesses motivation toward rewards or anticipatory reward processing, whereas the SHAPS assesses aspects of consummatory reward, or pleasure, which may account for these contrasting results. Collectively, these findings highlight a molecular mechanism that may address, in part, the pathogenesis of impaired DA functioning in anhedonia and stress-related psychopathologies and provides support for the role of stress in the emergence of anhedonia.

Keywords: Simultaneous PET-MR, Anhedonia, Stress, Dopamine

Disclosure: Nothing to disclose.

P389. Resting Brain Dynamics in Childhood Sexual Abuse and Major Depressive Disorder: A Coactivation Pattern Analysis

Emily Belleau*, Thomas Bolton, Roselinde Kaiser, Rachel Clegg, Emilia Cardenas, Franziska Goer, Pia Pechtel, Miranda Beltzer, Gordana Vitaliano, David Olson, Martin Teicher, Diego Pizzagalli

McLean Hospital - Harvard Medical School, Belmont, Massachusetts, United States

Background: Childhood maltreatment is a prominent risk factor for Major Depressive Disorder (MDD). Both childhood maltreatment and MDD putatively impact overlapping large-scale brain networks, including the default mode network (DMN), the frontoparietal network (FPN), and the salience network (SN). In addition to within-network functional abnormalities, childhood maltreatment and MDD have been separately linked to between-network dysfunction, including synchrony between the FPN and DMN. However, how child maltreatment and MDD may jointly or differentially influence these neural networks is unclear. Additionally, most the prior work has focused on examining static network properties, e.g., average network functional connectivity across the entire scan, a key gap given recent evidence that resting-state networks show dynamic changes in functioning over time. Distinct or overlapping dynamic network abnormalities related to MDD and childhood maltreatment remain unexplored.

Methods: Adult females, with and without a childhood sexual abuse (CSA) history, both healthy controls (HC; n = 22 without CSA, n = 14 with CSA) and MDD (n = 18 without CSA, n = 17 with CSA) participated in the study. Participants with CSA endorsed at least one incident of contact CSA between the ages of 5 to 14. All participants completed a resting state scan and filled out the Beck Depression Inventory II and the Response Styles Questionnaire (RSQ), a measure of rumination. Most participants (n = 62) also completed a third session, involving a psychosocial stressor. Cortisol samples and self-reported negative affect (NA) were collected at 5 times points, before, during, and after the stressor. For cortisol, area under the curve with respect to increase, a measure of stress-induced changes in cortisol levels, as well as the maximum level of NA reported during the stressor were calculated.

Neuroimaging data were subjected to whole-brain, voxel-wise coactivation pattern (CAP) analysis, which involves clustering the data to reveal transient network states of coordinated brain activity. The optimal number of CAPs was empirically determined using consensus clustering, which involves running k means clustering over several iterations, each time involving a randomly selected subsample of the data set and providing an index of clustering quality. Consensus clustering results indicated an optimal k of 8 and the 8 CAPs included an: 1) anterior DMN CAP, 2) SN CAP, 3) posterior DMN-FPN CAP, 4) visual system CAP, 5) prototypical DMN CAP, 6) dorsal attention network CAP, 7) somatosensory network CAP, and a 8) CAP involving prefrontal and posterior cingulate cortex regions. The following metrics were computed for each CAP: 1) time in CAP – the total number of volumes the participant spent in a CAP during the scan and 2) CAP transition frequencies – the number of times a specific CAP transitioned to another specific CAP divided by the total number of transitions.

A CSA (present/absent) x MDD (present/absent) MANCOVA was conducted on “time in CAP” across the 8 CAPs, controlling for fMRI motion metrics. Given that interactions between the DMN and FPN are implicated in MDD and CSA, CSA x MDD MANCOVAs were conducted on transitions involving DMN and FPN CAPs. Significant main effects and interactions were followed up with univariate ANCOVAs. CAPs showing group differences in “time in CAP” or “CAP transition frequencies” were correlated with depression and stress-related measures. Follow-up tests and correlations were corrected for multiple comparisons using FDR < 0.05.

Results: The MDD x CSA MANCOVA on “time in CAP” showed a significant main effect of MDD, Wilks Lambda =0.63, F (8, 58) = 4.22, p < 0.001. There was no significant main effect of CSA or MDD x CSA interaction, all ps > 0.20. Follow-up ANCOVAs indicated that, relative to HCs, individuals with MDD spent more time in a posterior DMN-FPN CAP, F (1,65) = 11.27, uncorrected p = 0.001, FDR-corrected p = 0.008. With respect to transition frequencies, two MDD x CSA MANCOVA’s were run, examining transitions between posterior DMN-FPN and anterior DMN CAPs as well as transitions between posterior DMN-FPN and prototypical DMN CAPs. Results from these analyses revealed a main effect of MDD, Wilk’s Lambda = 0.70, F (2,64) = 13.70, p < 0.001, but no main effect of CSA or MDD x CSA interaction all ps > .0.30, on posterior DMN-FPN -prototypical DMN transition frequencies. Specifically, individuals with MDD transitioned more frequently between posterior DMN-FPN and prototypical DMN CAPs than HCs. More time spent in a posterior DMN-FPN CAP and transitioning more frequently between posterior DMN-FPN and prototypical DMN CAPS was associated with higher RSQ rumination scores, partial rs .26-.33, FDR-corrected ps < 0.05. There were no significant associations between CAP metrics and BDI-II scores or stress reactivity measures, all ps > 0.05.

Conclusions: These findings are consistent with prior work establishing MDD as a disorder characterized by DMN-FPN imbalances, and linking DMN-FPN functional abnormalities to MDD-related cognitive dysfunction, including rumination. The lack of CSA findings is consistent with a prior study that failed to find child maltreatment-related abnormalities in time spent in distinct network states or transitioning between different states. However, these findings need to be replicated in larger sample sizes incorporating longitudinal designs.

Keywords: Major Depression Disorder, Childhood Maltreatment, Resting State Brain Dynamics, Coactivation Pattern Analysis, Rumination

Disclosure: Nothing to disclose.

P390. Prescription of Unfavorable Combinations of Drugs for Mood Disorders and Physical Conditions: A Cross-Sectional National Database Survey

Taisuke Yatomi*, Kuramochi Shin, Takahito Uchida, Hiroyoshi Takeuchi, Masaru Mimura, Hiroyuki Uchida

Keio University School of Medicine, Tokyo, Japan

Background: The aim of this cross-sectional study was to investigate prescriptions of unfavorable combinations of drugs for mood disorders and physical conditions.

Methods: We used the claims sampling data of 581,990 outpatients during January 2015 from the National Database of Health Insurance Claims and Specific Health Checkups of Japan provided by the Ministry of Health, Labor, and Welfare in Japan. Fisher’s exact test was performed to compare the prescription rates of (1) non-steroidal anti-inflammatory drugs (NSAIDs), loop/thiazide diuretics, angiotensin-converting enzyme (ACE) inhibitors, and/or angiotensin II receptor blockers (ARBs) between lithium users and age- and sex-matched non-lithium users; (2) NSAIDs, antiplatelet drugs, and/or anticoagulants between selective serotonin reuptake inhibitor (SSRI)/serotonin-noradrenaline reuptake inhibitor (SNRI) users and age- and sex- matched non-users; and (3) warfarin between mirtazapine users and age- and sex-matched non-users. A Bonferroni corrected p-value of <0.05/3 was considered statistically significant.

Results: Prescriptions of NSAIDs, loop/thiazide diuretics, ACE inhibitors, and/or ARBs were less frequently administered to lithium users (18.3%, n = 235/1,284) than to non-users (31.9%, n = 409/1,284) (p = 7.6×10-10). The prescription rates of NSAIDs, antiplatelet drugs, and/or anticoagulants were comparable between SSRI/SNRI users (23.1%, n = 3,078/13,330) and non-users (24.1%, n = 3,219/13,330) (p = 0.044). Warfarin was less frequently prescribed to mirtazapine users (0.78%, n = 18/2,300) than to non-users (1.65%, n = 38/2,300) (p = 0.01). Limitations: Actual treatment outcomes were not evaluated due to the cross-sectional study design.

Conclusions: A considerable proportion of patients receiving lithium, SSRIs/SNRIs or mirtazapine are treated with unfavorable polypharmacy. Further investigations are warranted to design interventions to reduce such pharmacotherapy for patients with mood disorders when necessary.

Keywords: Antidepressant, Bipolar Disorder, Depression, Lithium, Polypharmacy

Disclosure: Nothing to disclose.

P391. Nucleus Accumbens Mu Opioid Receptor Activation is Associated With Increase in Self-Esteem and Positive Mood After Experiencing Social Acceptance

Kathryn Hill*, David Hsu, Stephan Taylor, Ramin Parsey, Christine DeLorenzo

Stony Brook University, Stony Brook, New York, United States

Background: Rejection Sensitivity is the heightened expectation or perception of social rejection and is a feature of many psychiatric disorders including major depressive disorder, bipolar disorder, and borderline personality disorder. Endogenous opioid pathways have been shown to play a role in the neurological response to social rejection and reward. Our group has previously demonstrated that both social rejection and acceptance induced mu opioid receptor (MOR) activation and this activation was related to mood alterations. However, the MOR related biological underpinnings of Rejection Sensitivity and how MOR activation relates to mood changes over time have not yet been examined. In the present investigation, we examine the relationship between Rejection Sensitivity, MOR activation and change in mood over time following social rejection and acceptance. We hypothesize that those with higher trait Rejection Sensitivity will have lower MOR activation in both rejection and acceptance stimuli and that MOR activation will be related to changes in mood and self-esteem over time.

Methods: A total of 75 healthy participants (39 female, mean age = 21.1 +/- 2.2 years) completed socially relevant rejection and acceptance tasks during two back-to-back positron emission tomography (PET) scans using the MOR radioligand [11C]carfentanil. During and after each block, self-reported levels of self-esteem, desire for social interaction, and mood (“happy and accepted” or “sad and rejected”) were obtained. Trait Rejection Sensitivity was determined with the Adult Rejection Sensitivity Questionnaire at study initiation. Nondisplaceable binding potential (BPND) was calculated from bolus plus infusion delivery of tracer with occipital lobe reference-region based Logan graphical analysis. Task based MOR activation was determined by subtracting MOR BPND during acceptance or rejection from MOR BPND in the time-matched neutral block. MOR activation in the amygdala, midline thalamus, anterior insula, and nucleus accumbens were evaluated. Bonferroni correction for multiple comparisons was applied.

Results: MOR activation in the nucleus accumbens was positively associated with increase in ratings of self-esteem (p-value < 0.02 corrected, R = 0.35, 95% CI [0.10, 0.56]) and of feeling “happy and accepted” (p-value <0.03 corrected, R = 0.31, 95% CI [0.08, 0.51]) during the period between acceptance task administration and 5 minutes after the end of the acceptance task. MOR activation was not associated with change in desire for social interaction in relation to the acceptance task. Ratings of self-esteem or negative mood (“sad and rejected”) taken during and after the rejection task had no association with MOR activation. Trait Rejection Sensitivity scores were not related to MOR activation in the amygdala, midline thalamus, anterior insula, or nucleus accumbens during either acceptance or rejection tasks.

Conclusions: The present investigation demonstrated that MOR activation in the nucleus accumbens was associated with increased self-esteem and positive mood after experiencing social acceptance. Contrary to our hypothesis, Trait Rejection Sensitivity was not related to MOR activation in the amygdala, midline thalamus, anterior insula, and nucleus accumbens as shown through region-based analysis. This suggests that in healthy individuals, the regional endogenous opioid response to social acceptance is independent of this trait.

Keywords: Mu-Opioid Receptor Binding Potential, Social Rejection, Self-Esteem, Mood, PET Imaging

Disclosure: Nothing to disclose.

P392. Intensive TMS in Treatment Refractory Patients with Major Depressive Disorder: A Pilot Replication

Yvette Sheline*, Nicholas Balderston, Desmond Oathes, Walid Makhoul, Romain Duprat, Joanne Beer, Tommaso Girelli, Zafiris Daskalakis

Center for Neuromodulation in Depression and Stress, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States

Background: Approximately 30% - 40% of patients with major depressive disorder (MDD) have treatment resistant depression (TRD), defined as a failure to respond to two adequate medication trials or relapse during treatment. Patients with TRD experience severe depressive symptoms, including suicidal ideation. Transcranial magnetic stimulation (TMS) has proven efficacy for the treatment of TRD but is still relatively under-utilized, and, like most depression treatments, there is a delay in the onset of beneficial effects of TMS, generally administered as a 4 week course. Few evidence-based interventions exist for depression treatment with rapid onset. Thus, testing the efficacy of rapid-acting treatments could potentially help short-circuit the descent into suicidal states and could accelerate recovery. In this study we sought to replicate a recently developed protocol (Williams, Sudheimer et al. 2018) for concentrating the usual 4 weeks of TMS into 5 days of intensive treatment using the same treatment parameters in a treatment refractory cohort.

Methods: Participants (n = 7) were recruited from the outpatient clinics at the University of Pennsylvania. Participants (age 21-67; mean = 41.4; 4 males, 3 females) were required to meet criteria for unipolar TRD. They were excluded for symptoms of psychosis, other comorbid psychiatric illness including PTSD, OCD and substance abuse disorder, neurological syndromes including Parkinson’s disease, seizure disorder, history of significant brain trauma, space occupying lesion, dementia, any serious medical illness (e.g. end stage renal disease), use of medications that could produce depression (e.g. beta-blockers) or MRI contraindications. All were assessed by SCID, Montgomery Asberg Depression Rating Scale (MADRS) and Scale for Suicidal Ideation (SSI) to determine if patients met inclusion and exclusion criteria. All underwent MRI scanning (Siemens 3T scanner) to obtain coordinates for neuronavigation guided TMS. Individualized targeting was conducted by selecting the dorsal lateral PFC coordinates corresponding to the gyral crest at the center of a meta-analytically derived DLPFC mask from Neurosynth (i.e. largest left hemisphere cluster using association test search term = dlPFC; z = 5.93 peak = -46, 38, 30) superimposed on each individual brain. The study was approved by the University of Pennsylvania Institutional Review Board. Participants were treated with open-label iTBS with 1800 pulses per session at 90% resting motor threshold and depth adjustment to the personalized anatomical target. Each session lasted 10min followed by a 50-min intersession interval. Our iTBS pulse parameters were identical to those used by Li et al. (Li, Chen et al. 2014) (3-pulse 50-Hz bursts at 5-Hz for 2-s trains, with trains every 10s). Ten sessions were applied per day (18000 pulses/day) for five consecutive days (90000 total pulses) using a Magventure Magpro X100 system. Depression severity was measured at baseline, immediately after the final session and at 2 weeks follow-up. To assess intensive TMS-induced changes in symptom severity from baseline, linear mixed effects regression models fit by restricted maximum likelihood (REML) were used with subject-level random intercepts. P-values for fixed-effects parameter estimates were estimated using Kenward-Roger’s approximation and assessed individually at a 0.05 significance level.

Results: Participants had a history of a mean of 6.6 failed treatment trials with antidepressant monotherapy and mean of 2.4 augmentation trials. All participants were significantly impaired by illness resulting in either unemployment or disability. MADRS scores significantly decreased following treatment (β = -12.7, se = 2.8, p < 0.001) and remained significant 2-weeks post-treatment (β = -12.4, se = 3.0, p = 0.002). SSI scores significantly decreased following treatment (β = -2.7, se = 0.9, p = 0.015) and remained low but not statistically different from baseline at 2-weeks post-treatment (β = -2.1, se = 1.0, p = 0.06). All participants tolerated the therapy without adverse events.

Conclusions: This work confirms previously reported evidence for treatment of highly refractory depression with high-dose spaced iTBS. An important difference between this study and the Williams et al study (Stanford SAINT protocol) is the use of anatomical targeting rather than connectivity based targeting, which may have resulted in a less robust treatment response in the current study (37% vs 76% decrease). Nonetheless, we note that the patients who were treated in this study achieved an equivalent or better response in 5 days compared with traditional TMS lasting 4-6 weeks. We are planning a follow-up study with connectivity guided TMS to confirm the added benefit. A sham controlled study will be necessary to assess the treatment outcome in a larger sample of TRD patients.

Keywords: TMS, Major Depressive Disorder (MDD), MRI, Treatment Resistant Depression

Disclosure: Nothing to disclose.

P393. Thalamic Structure and Function in Youth With and At Familial Risk for Bipolar Disorder

Manpreet Singh*, Aaron Gorelik, Kayla Carta, Mark Gorelik, Kiki Chang, Jennifer Bruno, Akua Nimarko

Stanford University School of Medicine, Stanford, California, United States

Background: Youth with and at familial risk for bipolar disorder have aberrant reward function in key prefrontal-striatal networks. However, thalamic structure, function, and connectivity associated with trait and state features of bipolar disorder before and around emergent mania is poorly understood.

Methods: Youth with (n = 22) versus without (n = 23) BD underwent structural neuroimaging during reward processing using the monetary incentive delay (MID) task at baseline and 12 months. Healthy Youth at high and low risk for mood disorders [BD-risk (n = 40), MDD-risk (n = 41), and HC (n = 45) [mean age 13.09 +/- 2.58, 56.3% female] also completed the MID task at baseline and were followed for behavioral and clinical outcomes over 4.37 +/- 2.29 years. Region of interest (ROI) analyses were conducted using an anatomically defined thalamus seed during reward anticipation and feedback. Psychophysiological interaction and whole-brain voxel-wise group differences were also conducted (Z > 3.1; FWE-cluster corrected p < .05). We also used machine learning (ML) techniques to evaluate whether neural correlates during reward processing with additional features could predict risk group membership. Based on previous studies that have shown success with classifying fMRI-based data with limited sample datasets, two machine learning techniques were evaluated: Support Vector Machine (SVM) and Random Forest.

Results: Relative to healthy controls, adolescents with BD showed greater reductions in thalamic volume from baseline to 12-month follow up (Treatment x time interaction, Left thalamus: F(45) = 8.38, p = 0.006; Right thalamus: F(45) = 3.96, p = .05). Among BD youth, reductions in both hemispheres were negatively associated with mania symptom improvement/maintenance (p < 0.05). Relative to MDD-risk and HC, BD-risk had decreased activation of the thalamus during anticipation of monetary gain F(2,118) = 4.64; p = .01 (FDR-corrected p = .04). BD-risk had less connectivity between the thalamus and left middle frontal gyrus (Z > 3.1; p < .001) and left superior temporal gyrus (Z > 3.1; p < .05) compared to MDD-risk. Voxel-wise, BD-risk had decreased activation in the cerebellum during anticipation and outcome of monetary gain relative to MDD-risk and HC (Z > 3.1; p < .001; Z > 3.1; p < .01, respectively). Decreased thalamic connectivity was associated with increased impulsivity at baseline and reduced prosocial behavior at follow-up. The best performing ML technique was a random forest with an average accuracy of 63.7% (SD 8%).

Conclusions: Compared to typically developing youth, BD youth showed statistically significant volumetric reductions in both the left and right thalamus over the course of 12 months, such that those with worsening scores had greater reductions in volume even after accounting for treatment, suggesting a possible disorder related phenomenon. Reduced thalamic activation and connectivity during reward processing may distinguish familial risk for BD from familial risk for MDD and represent early markers of vulnerability that precede symptom onset and may herald social dysfunction later in development. SVM and Random Forest ML models were able to accurately predict risk group membership based on thalamus activation and connectivity, impulsivity, and approach-withdrawal beyond chance. These findings suggest that BD-risk and MDD-risk youth may present with a combination of specific neural signatures and behaviors related to reward processing that are common and distinct. Differential activation and connectivity of the thalamus could be specific to BD, which has been suggested in previous studies of youth with and at-risk for BD. While preliminary, our findings highlight potential targets and risk factors that could be used to distinguish youth at risk for BD from youth at risk for MDD, and also possibly improve approaches to prevention and treatment selection for youth at familial risk for mood disorders.

Keywords: Pediatric Bipolar Disorder, Thalamus, Reward Processing

Disclosure: National Institutes of Health, Brain and Behavior Research Foundation, Johnson and Johnson, Stanford University Maternal Child Health Research Institute, Stanford University Department of Psychiatry: Grant (Self)

Sunovion, Skyland Trail: Advisory Board (Self)

X, moonshot factory, Alphabet, Inc., Limbix: Consultant (Self)

American Psychiatric Association, Thrive Global: Royalties (Self)

P394. Structural MRI-Based Brain Age as a Reliable Biomarker of Response to Antidepressant Treatment: Findings From the EMBARC Study

Cherise Chin Fatt, Manish Jha, Abu Minhajuddin, Taryn Mayes, Madhukar Trivedi*

The University of Texas Southwestern Medical Center, Dallas, Texas, United States

Background: Recent reports suggest that adults with major depressive disorder (MDD) have higher neuroimaging-predicted brain age as compared to their chronological age, i.e., have accelerated brain aging. Furthermore, accelerated brain aging in adults with MDD has been linked to greater impulsivity and increased depression severity. While promising, it remains unclear whether neuroimaging-predicted brain age can be a useful biomarker in prognosticating clinical outcomes. Therefore, to establish brain age as a clinically useful biomarker we first checked its reliability using structural brain scans that were acquired approximately one week apart, and then evaluated changes in depression severity based on pre-treatment brain age using data from the Establishing Moderators and Biosignatures of Antidepressant Response in Clinical Care (EMBARC) study.

Methods: Brain age was estimated using T1-weighted structural MRI scans and a previously-published Gaussian Processes Regression model (https://doi.org/10.5281/zenodo.3476365) at baseline (n = 290) and week-1 (n = 260) of EMBARC study. Participation in the EMBARC study was restricted to adults with MDD who were (1) in a currently depressive episode of at least moderate severity, (2) unmedicated and (3) willing to be randomized to either sertraline or placebo. Overall depression severity was measured with the 17-item Hamilton Depression Rating Scale (HAMD-17) at baseline, weeks 1, 2, 3, 4, 6, and 8. Δ brain age was computed as follows: (neuroimaging-predicted brain age) minus (chronological age). Comparison of brain age values at baseline and week-1 of EMBARC were conducted by using correlation analyses, Bland Altman analyses, and paired t-tests. Separate repeated measures mixed model analyses for sertraline and placebo were used to evaluate with changes in depression severity (dependent variable) differed on the basis of pre-treatment Δ brain age after controlling for age, race, ethnicity, sex and site.

Results: Mean [standard deviation (SD)] chronological age of EMBARC study participants at baseline was 37.1 (13.3) years. Mean (SD) neuroimaging-predicted brain ages at baseline (n = 290) and week-1 (n = 260) of EMBARC were 40.6 (13.1) and 41.0 (13.2) years, respectively. Brain age values at baseline and week-1 were highly correlated (Pearson’s r = 0.98, n = 260, p < 0.0001). Furthermore, there was no significant difference in brain age at baseline and week-1 (mean difference = 0.23 years, 95% Confidence Interval: -0.09 years, 0.55 years).

On average, individuals with MDD had higher neuroimaging-predicted brain age than chronological age at the baseline visit of EMBARC [mean (SD) Δ brain age = 3.1 (6.1) years]. Δ brain age and overall depression severity were not associated at baseline (Pearson’s r = -0.06, p = 0.29). However, Δ brain age at baseline significantly predicted changes in depression severity with sertraline (Δ brain age-by-week interaction: F = 2.54, df = 6. 695, p = 0.019) but not with placebo (p = 0.64) after controlling for age, gender, race, ethnicity, and site. Among EMBARC participants treated with sertraline, higher Δ brain age was associated with smaller reductions in depression severity from baseline-to-week-8.

Conclusions: In this large sample of adults with MDD, we found that brain age values based on structural MRI scans 1-week apart were highly correlated and reliable. Additionally, accelerated brain aging (i.e., higher Δ brain age) was associated with poorer outcomes with sertraline. No such association between accelerated brain aging and treatment response was seen among participants who were treated with placebo.

Keywords: Biomarker, Brain age, Antidepressant Treatment

Disclosure: Alto Neuroscience, Axsome, Sage, GH Research Limited, GreenLight VitalSign6 Inc.: Advisory Board (Self)

Janssen, Otsuka, Acadia Pharmaceuticals, Inc., Alkermes Inc., Merck Sharp and Dohme Corp., Mind Medicine (MindMed) Inc., Neurocrine Biosciences Inc., Orexo US Inc., Signant Health, Titan Pharmaceuticals, Inc.: Consultant (Self)

Oxford University Press: Royalties (Self)

P395. The Role of Mitochondrial DNA in Mediating Chronic Stress-Induced Inflammation and Behavior

Ashutosh Tripathi, Carl Whitehead, Anilkumar Pillai*

University of Texas Health Science Center at Houston, Texas, Houston, Texas, United States

Background: A better understanding of how stressful experiences accelerate behavioral abnormalities can help to improve the treatment options. Chronic stress can also provoke elevated inflammation and exaggerated inflammatory responses in both humans and animal models. Although much of the prior studies have focused on the innate immune system, the mechanisms that link adaptive immunity to chronic stress-induced behavioral abnormalities are not well understood. Mitochondria, the powerhouse of cell, become damaged and dysfunctional following chronic stress conditions, raising the question of whether inflammation associated with chronic stress-related neuropsychiatric conditions is due to mitochondria-induced inflammation. In the present study, we investigated the role of mitochondrial DNA (mtDNA) from CD4 + T cells in mediating chronic stress-induced behavioral changes.

Methods: Adult male ICR, mitochondrial antiviral signaling protein (MAVS) knock out (KO), and Toll-like receptor 9 (TLR9) KO mice were used. The chronic restraint stress (RS) model was used to examine the effects of chronic stress on neurobehavior. Social behavior was tested in a three-chamber test. mRNA levels were measured by quantitative RT-PCR. Neutrophil Extracellular Traps (NETs) formation was measured by ELISA. The data were analyzed by two-way ANOVA.

Results: Antibody-mediated depletion of CD4 + T cells (but not CD8 + T cells), as well as treatment with Rapamycin (a known stimulator of mitophagy), significantly attenuated (p < 0.05) RS-induced increases in cell-free (cf)-mtDNA, NETs formation, and social behavior deficits in mice. RS induced a decrease in the expression of NOD-like receptor X1 (NLRX1, a mitochondrial protein known to promotes autophagy, but attenuates IFN-I production via promoting the degradation of MAVS) in CD4 + T cells. Further, activation of NLRX1 signaling using MAVS KO mice attenuated RS-induced increases in serum cf-mtDNA, NETs, and behavior deficits. In addition, Inhibition of TLR9 attenuated mtDNA-induced increases in NETs and behavior deficits.

Conclusions: Our findings show an important role of mtDNA in mediating chronic stress-induced inflammation and behavior in mice.

Keywords: mtDNA, Chronic Stress, Inflammation, Social Behavior, Mitophagy

Disclosure: Nothing to disclose.

P396. Alternative Splicing Mechanisms and Chronic Stress

Ma-Li Wong, Eunice Chin, Hongyu Ruan, Jianhua Chen, Qi Ma, Julio Licinio*

SUNY Upstate Medical Center, Syracuse, New York, United States

Background: Chronic stress is a significant risk factor for several psychiatric and neuropsychiatric disorders, including major depressive disorder, schizophrenia, and post-stress traumatic disorder. Preclinical and clinical studies substantiate the effect of stress on neurotransmission and synaptic plasticity in brain regions related with behavioral responses, leading to long-term neuronal dysregulation, and changed emotional and cognitive behaviors. More than 70% of human genes undergo alternative splicing, and about a third of diseases are the result of errors in pre-mRNA splicing. Splicing mechanisms are especially vital in the central nervous system (CNS), as vast numbers of genes that are critical for neuronal differentiation, function, and survival are known to undergo alternative splicing. This study will investigate the novel functional role of an essential splicing factor, CWC22 (spliceosome-associated protein CWC22), in alternative splicing of genesthat may contribute to neuronal dysfunction in chronic stress. CWC22 was initially shown to be a marker of antidepressant treatment response in Mexican-Americans (Wong ML et al. J Affect Disord. 2021;279:491-500), and it was subsequently identified as a male-associated suicidality risk locus in a multivariate gene-by-environment genome-wide interaction study (GEWIS) of suicidality in 123,633 individuals (Wendt FR et al. Neurobiol Stress. 2021 Feb 18;14:100309).

Methods: Male C57BL/6 mice were submitted to chronic restraint stress (CRS); control mice were non-stressed. Behavior despair and anxiety were assessed using behavioral tests. Plasma was collected to measure corticosterone levels. CWC22 levels in brain tissues were determined by Western blots, immunohistochemistry, and RT-PCR. CWC22 knockdown in primary hippocampal neurons were generated using shRNA and control lentiviruses. Day-in-vitro 14 neurons were recorded using Whole-cell patch clamp. All behavioral scoring and data analyses was conducted with the experimenter blinded to the group. Experiments involving cells were repeated at least 3 times with independent batches of cells. Viral vectors were generated by us and sequence-verified. Student’s t-test was used to compare 2 groups and Mann Whitney test was used for non-normal data. α was set at 0.05; a p value of < 0.05 was considered significant as mean differences have a 95% probability of not being due to chance. Viral vector efficiency and sequence was verified before use.

Results: CRS animals displayed decreased time spent in the center of the open field (P < 0.001),

decreased sucrose preference (P < 0.001), increased immobility time in the forced swim test (P < 0.001) and corticosterone levels (P < 0.05) in comparison to non-stressed mice (n = 12-14). CWC22 is highly expressed in CNS tissues. Hippocampal CWC22 protein levels were reduced in CRS animals in comparison to non-stressed controls (P < 0.05; n = 8). CWC22 knockdown neurons had significantly reduced mean mEPSC (miniature excitatory postsynaptic current) frequency and amplitude (P < 0.01, n = 20). Both SYN1 (synapsin 1)-positive puncta and PDS95 (postsynaptic density protein 95)-positive puncta were increased in CWC22 knockdown neurons; P < 0.001 (n = 4-15 neurites/condition). The number of dendritic spines labeled with GFP was increased by CWC22 knockdown (P < 0.01), and further analysis of spine morphology revealed that mushroom spines’ (considered to be ‘memory’ spines), and thin spines (called ‘learning’ spines) density, were increased (both at P < 0.001; n = 4-15 neurites/condition). Gria1 Pre-mRNA splicing was reduced in CWC22 depleted hippocampal neurons (P < 0.001). New and unpublished data include: 1) CWC22 expression in CNS tissues; 2) change in hippocampal CWC22 protein levels in CRS animals; 3) All molecular biology and in vitro data; 4) Viral vector constructs.

Conclusions: Splicing events have been reported for many genes in the central nervous system (CNS), and pre-mRNA splicing is a major neuronal mechanism for adaptation to stress. Elucidating the specific roles of spliceosomal components in the CNS may clarify how dysfunction of pre-mRNA splicing affects its functional integrity and provide novel insights into the etiology of stress-related neuropsychiatric disorders. Our studies indicate that CWC22 dysregulation in chronic stress can lead to hippocampal neuronal dysfunction and in vitro results also support the role of CWC22 in synapse formation and dendritic spine morphology. Taken together, our data suggest that CWC22 is a negative regulator of synaptic plasticity.

Keywords: Splice Variants, Stress, Synspsis, Hippocampus, Major Depression

Disclosure: National Institutes of Health, CART Foundation: Grant (Self & Spouse)

Springer Nature: Honoraria (Self)

eLife Sciences Publications: Honoraria (Spouse)

P397. Functional Network Connectome Abnormalities Associated With Familial Risk for Developing Bipolar I Disorder in Youth With Attention-Deficit/Hyperactivity Disorder

Kun Qin, Du Lei, Ziyu Zhu, Maxwell Tallman, L. Rodrigo Patino, David Fleck, Veronica Aghera, Robert McNamara*, Melissa DelBello

University of Cincinnati College of Medicine, Cincinnati, Ohio, United States

Background: Comorbid attention-deficit/hyperactivity disorder (ADHD) is highly prevalent in youth with bipolar I disorder (BD-I), and ADHD symptoms commonly precede the initial onset of mania and reduce the age at onset of mood symptoms. Having a first-degree relative with BD-I substantially increases the risk of developing BD-I, and there is a high prevalence of ADHD in youth with a first-degree relative with BD-I. Although youth with a first-degree relative with BD-I and ADHD symptoms are at elevated risk for developing BD-I, associated central pathophysiological mechanisms are poorly understood. The initial onset of BD-I frequently occurs during adolescence, a developmental period associated with robust maturational changes in prefrontal cortex structural and functional connectivity. Graph theory analysis is increasingly being used to characterize topological properties of brain network organization and connectivity. In this cross-sectional resting-state MRI study, we characterized the topology of the functional connectome in ADHD youth with (high-risk) and without (mid-risk) a first-degree relative with BD-I and a healthy comparison group (low-risk). Exploratory analyses evaluated associations between functional topological metrics and clinical measures of ADHD and mood symptom severity.

Methods: Resting-state MRI scans were acquired from n = 37 adolescents with ADHD and at least one biological parent or sibling with BD-I (high-risk), n = 45 ADHD adolescents with no first- or second-degree relative with a mood or psychotic disorder (mid-risk), and n = 32 healthy adolescents with no personal or family history of a DSM-5 Axis I psychiatric disorder (HC, low-risk). All ADHD patients met DSM-5 criteria for ADHD (all types), had no exposure to psychostimulants for at least 3 months prior to scanning, and had no comorbid mood, anxiety, conduct, eating or psychotic disorders. Whole-brain functional connectivity network was constructed for each participant. Global- and nodal-level network topological properties were calculated based on individual functional networks using graph theoretical analysis. Global topological metrics included global efficiency (Eglob), local efficiency (Eloc), clustering coefficient (Cp), characteristic path length (Lp), normalized clustering coefficient (γ), normalized characteristic path length (λ) and small-worldness scalar (σ). The nodal topological metrics reflecting centrality included degree, betweenness, and efficiency. The comparison of network topological metrics across groups and post-hoc analyses were conducted using the non-parametric permutation analysis (10000 permutations) with a one-way ANOVA model. Bonferroni correction was applied for subsequent post-hoc pairwise comparisons. Correlation analyses evaluated associations between significantly different functional topological metrics and clinical measures of mood and ADHD symptom severity, and FDR correction was applied to control for false positives.

Results: A total of n = 114 psychostimulant-free adolescents were included in the functional connectome analysis, and there were no group differences in age, sex, or BMI. Significant group differences were observed for the global topological metrics Eglob (p = 0.026) and Lp (p = 0.028). Eglob was significantly decreased (p = 0.005) and Lp (p = 0.003) increased in mid-risk ADHD adolescents compared to low-risk HC subjects. Brain regions with significant group differences in at least two of three nodal topological metrics included the left dorsolateral superior frontal gyrus (SFG), right middle orbitofrontal cortex (OFC), right hippocampus, left amygdala, left inferior parietal lobule (IPL) and right middle temporal pole (MTG). Compared with low-risk HC subjects, high-risk ADHD adolescents exhibited abnormal nodal topological centralities in the left dorsolateral SFG, right hippocampus and right MTG, whereas mid-risk ADHD adolescents exhibited abnormalities in the right middle OFC, right hippocampus, and left amygdala. Significant differences between high-risk and mid-risk ADHD groups were found in the left IPL. Among all ADHD subjects, the degree (r = -0.28, p = 0.002) and efficiency (r = -0.27, p = 0.003) of the right hippocampus, and the degree (r = -0.27, p = 0.003) and efficiency (r = -0.27, p = 0.003) of the right middle OFC, were inversely correlated with ADHD-RS total score. Hyperactive/impulsive scores were inversely correlated with global efficiency (r = -0.25, p = 0.007) and right hippocampus degree (r = -0.29, p = 0.002), and positively correlated with characteristic path length (r = 0.26, p = 0.005) and betweenness (r = 0.29, p = 0.001) of left dorsolateral SFG. The degree (r = 0.27, p = 0.004) and betweenness (r = 0.25, p = 0.007) of the left dorsolateral SFG was positively correlated with YMRS total scores.

Conclusions: This cross-sectional analysis found that youth at mid- and high-risk for developing BD-I exhibit patterns of functional network abnormalities compared with low-risk youth. Common abnormal regional centralities were observed in the right hippocampus for all ADHD adolescents regardless of risk for developing BD-I, whereas high-risk subjects exhibited unique abnormalities in topological metrics in the inferior parietal gyrus. These findings suggest that familial risk for BD-I in conjunction with ADHD is associated with a pattern of regional functional network topological abnormalities that may represent a unique prodromal phenotype.

Keywords: Bipolar Disorder, Familial Risk, ADHD

Disclosure: Nothing to disclose.

P398. Brain Network Structural Connectome Abnormalities in Adolescents at Varying Risk for Bipolar I Disorder: A Cross-Sectional MRI Study

Ziyu Zhu, Du Lei, Kun Qin, Maxwell Tallman, L. Rodrigo Patino, David Fleck, Veronica Aghera, Robert McNamara*, Melissa DelBello

University of Cincinnati College of Medicine, Cincinnati, Ohio, United States

Background: Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that significantly increases risk for developing other psychiatric disorders including bipolar I disorder (BD-I). Comorbid ADHD is highly prevalent in youth with BD-I, and ADHD symptoms commonly precede the initial onset of mania and reduce the age at onset of mood symptoms. Having a first-degree relative with BD-I also significantly increases the risk for developing BD-I, and there is high prevalence of ADHD in youth with a first-degree relative with BD-I. Furthermore, the initial onset of mania, and by definition BD-I, frequently occurs during adolescence, a developmental period associated with robust maturational changes in prefrontal cortex structural and functional connectivity. Previous structural MRI studies have found that youth with BD-I or ADHD exhibit morphological abnormalities in prefrontal brain regions compared with healthy typically developing youth. However, the majority of prior studies did not control for familial risk of BD-I, ADHD comorbidity, and/or psychostimulant exposure, and there have been no studies that have directly compared psychostimulant-free ADHD youth with and without a first-degree relative with BD-I. In this cross-sectional study, we used graph-based network analysis based on structural MRI data to interrogate topological properties of brain networks in ADHD adolescents with and without a first-degree relative with BD-I and a healthy control group. We additionally evaluated relationships between topological metrics and mood and ADHD symptom ratings.

Methods: Three groups of psychostimulant-free adolescents (10-18 years) were recruited: adolescents with ADHD and at least one biological parent or sibling with BD-I (high-risk), adolescents with ADHD and no first- or second-degree relative with a mood or psychotic disorder (mid-risk), and healthy adolescents with no personal or family history of psychiatric illness (HC, low-risk). High-resolution 3D T1-weighted images were collected using a Philips 3.0 T MR scanner. Brain networks were constructed based on the similarity of morphological features across regions and analyzed using a graph theory approach. Network metrics, which include seven global-level graph metrics (characteristic path length, clustering coefficient, normalized clustering coefficient, normalized characteristic path length, small-worldness, global efficiency, and local efficiency) and three nodal-level properties (degree, efficiency and betweenness) were calculated. We used ANOVA models to compare the structural connectome characteristics across groups, and post hoc pairwise permutation tests were conducted for measures that differed between groups. Significant topological metrics with p < 0.05 were reported. Partial correlation analysis was used to assess the relationships between each topological metric and clinical measures of mood and ADHD symptom severity variables. The potential confounding effects of age and sex were controlled for in the models, and the threshold for results were set to an expected FDR of 5% to correct for multiple comparisons.

Results: A total of n = 149 adolescents (mean age: 14.1 ± 2.5 years, 36% female) were included in the analysis (low-risk, n = 49; mid-risk, n = 50; high-risk, n = 50). No significant group differences were observed for age, sex, or BMI. The mid-risk and high-risk ADHD groups exhibited similar differences when compared with low-risk HC subjects, mainly in the default-mode network (DMN) and central executive network (CEN), including bilateral gyrus rectus, right superior parietal gyrus, and right triangular inferior frontal gyrus. Topological alterations in the salience network (SN), including right opercular inferior frontal gyrus and right pallidum, were found between the high-risk group and both mid- and low-risk groups. Significant abnormalities in global network properties were found only in the high-risk group when compared with low-risk HC group, which included reduced characteristic path length (p = 0.008), increased global efficiency (p = 0.008), and increased local efficiency (p = 0.041). ADHD-RS hyperactivity/impulsivity subscale scores were positively correlated with the degree (r = 0.34, p = 0.001) and nodal efficiency (r = 0.27, p = 0.008) of right triangular inferior frontal gyrus. There were no significant correlations between topological metrics and mood symptom ratings after correcting for multiple comparisons.

Conclusions: Both high- and mid-risk ADHD adolescents exhibit topological alterations in three major intrinsic connectivity networks (i.e., CEN, DMN and SN) compared to low-risk HC subjects. However, topological alterations in the SN were only observed in the high-risk group. These findings suggest that familial risk for BD-I in conjunction with ADHD is associated with different regional structural network abnormalities compared with ADHD alone and may represent a unique prodromal phenotype relevant to the risk for developing BD-I.

Keywords: Bipolar Disorder, Familial Risk, ADHD

Disclosure: Nothing to disclose.

P399. Cross-Sectional Evaluation of Prefrontal Neurochemistry and Prodromal Mood Symptoms in Youth at Varying Risk for Bipolar I Disorder

Constance Chen, Maxwell Tallman, Kim Cecil, Du Lei, L. Rodrigo Patino, Veronica Aghera, Melissa DelBello*, Robert McNamara

University of Cincinnati, Cincinnati, Ohio, United States

Background: The initial onset of bipolar I disorder (BD-I) frequently occurs during adolescence, and having a first-degree relative with BD-I substantially increases the risk of developing BD-I. Additionally, attention deficit/hyperactivity disorder (ADHD) is a risk factor for psychopathology including BD-I, and there is a high prevalence of ADHD in youth with BD-I or a first-degree relative with BD-I. Furthermore, ADHD symptoms commonly precede the initial onset of BD-I and are associated with an earlier onset of mood symptoms. Although adolescents with ADHD and a first-degree relative with BD-I are at elevated risk for developing mood disorders, associated prodromal clinical and neurophysiological features remain poorly understood. Proton magnetic resonance spectroscopy (1H MRS) studies have previously found that youth with BD-I or ADHD exhibit abnormalities in prefrontal neurochemistry compared with healthy typically developing youth. However, the majority of prior studies did not control for familial risk of BD-I, ADHD comorbidity, and/or psychostimulant exposure, and there have been no studies that have directly compared psychostimulant-free ADHD youth with and without a first-degree relative with BD-I. In this cross-sectional study, we characterized mood and cognitive symptoms and used 1H MRS to investigate bilateral ventrolateral prefrontal cortex (VLPFC) neurochemistry in ADHD youth with (high-risk) and without (mid-risk) a first-degree relative with BD-I and a healthy comparison group (low-risk). Exploratory analyses evaluated associations between VLPFC neurochemistry and mood and ADHD symptom severity.

Methods: A total of n = 150 male and female (65% male) psychostimulant-free adolescents (mean age: 14.1 ± 2.5 years) were enrolled into three groups: adolescents with ADHD and at least one biological parent or sibling with BD-I (high-risk, n = 50), adolescents with ADHD and no first- or second-degree relative with a mood or psychotic disorder (mid-risk, n = 51), and healthy adolescents with no personal or family history of a DSM-5 Axis I psychiatric disorder (low-risk, n = 49). All ADHD patients met DSM-5 criteria for ADHD (all types), had no exposure to psychostimulants for at least 3 months prior to scanning, and had no comorbid mood, anxiety, conduct, eating or psychotic disorders. ADHD (ADHD-RS), mania (YMRS), depression (CDRS-R), and global functioning (CGAS) ratings were determined, and 1H MRS scans performed using a Philips 3.0 T MR scanner. MRS voxels (20 × 20 × 20 mm) were positioned in the right and left VLPFC, and glutamate (Glu), glutamate+glutamine (Glx), myo-inositol (mI), choline (Cho), N-acetyl aspartate (NAA), and phosphocreatine plus creatine (PCr + Cr) concentrations determined.

Results: There were no significant group differences in age (p = 0.25), sex (p = 0.83), race (p = 0.28), or BMI (p = 0.40). Significant group differences were observed for ADHD-RS total score (p < 0.0001), as well as inattentive (p < 0.0001) and hyperactivity/impulsivity (p < 0.0001) subscores, YMRS total score (p < 0.0001), CDRS-R total score (p < 0.0001), and CGAS total score (p < 0.0001). Pairwise comparisons found that both high-risk and mid-risk groups differed significantly from low-risk on all rating measures, and high-risk subjects had significantly higher hyperactivity/impulsivity subscores (p = 0.004), YMRS total scores (p = 0.0006), and CDRS-R total scores (p = 0.006) compared with low-risk subjects. For the 1H MRS analysis, a total of n = 143 subjects were included: high-risk, n = 47; mid-risk, n = 48; low-risk, n = 48. For the right VLPFC, no significant group differences were observed for Glu (p = 0.27), Glx (p = 0.24), mI (p = 0.19), Cho (p = 0.84), NAA (p = 0.63), or PCr + Cr (p = 0.55). For the left VLPFC, no significant group differences were observed for Glu (p = 0.84), Glx (p = 0.82), mI (p = 0.15), Cho (p = 0.53), NAA (p = 0.53), and PCr + Cr (p = 0.69). Among all subjects (n = 143), CDRS-R (r = 0.18, p = 0.03) and YMRS (r = 0.19, p = 0.03) total scores were positively correlated with right VLPFC NAA. CDRS-R scores were inversely correlated with left VLPFC Cho (r = -0.18, p = 0.03) and Glx (r = -0.18, p = 0.03), and YMRS scores were inversely correlated with left VLPFC Glx (r = -0.21, p = 0.04).

Conclusions: This cross-sectional analysis found that youth at high-risk for developing BD-I exhibit greater depression and manic symptom severity, as well as greater hyperactivity/impulsivity symptoms, compared with mid- and low-risk youth. These prodromal symptoms may represent early indices of progressive mood symptom dysregulation that could facilitate risk assessment and management. Although neither high-risk nor mid-risk youth exhibited significant abnormalities in prefrontal neurochemistry, associations between mood symptoms and prefrontal NAA, Cho, and Glx warrant additional investigation.

Keywords: Bipolar Disorder, Familial Risk, ADHD

Disclosure: Alkermes, Allergan, Sunovion: Consultant (Self)

Janssen, Johnson and Johnson, Lundbeck, Sage, Myriad: Advisory Board (Self)

Sunovion: Honoraria (Self),

P400. Ketamine Decreases Neuronally Released Glutamate via Retrograde Stimulation of Presynaptic Adenosine A1 Receptors

Vesna Lazarevic, Yunting Yang, Ivana Flais, Per Svenningson*

Karolinska Institutet, Stockholm, Sweden

Background: Ketamine produces a rapid antidepressant response in patients with major depressive disorder (MDD), but the underlying mechanisms appear multifaceted. One hypothesis, proposes that by antagonizing NMDA receptors on GABAergic interneurons, ketamine disinhibits afferens to glutamatergic principal neurons and increases extracellular glutamate levels. However, ketamine seems also to reduce rapid glutamate release at some synapses. Therefore, clinical studies in MDD patients have stressed the need to identify mechanisms whereby ketamine decreases presynaptic activity and glutamate release.

Methods: The effect of ketamine and its antidepressant metabolite, (2R,6R)-HNK, on neuronally derived glutamate release was examined in rodents. We used FAST methodology to measure depolarization-evoked extracellular glutamate levels in vivo in freely moving or anesthetized animals, synaptosomes to detect synaptic recycling ex vivo and primary cortical neurons to perform functional imaging and to examine intracellular signaling in vitro.

Results: In all used approaches, ketamine and (2R,6R)-HNK reduced glutamate release in a manner which could be blocked by AMPA receptor antagonism. Antagonism of adenosine A1 receptors, which are almost exclusively expressed at nerve terminals, also counteracted ketamine’s effect on glutamate release and presynaptic activity. Signal transduction studies in primary neuronal cultures demonstrated that ketamine reduced P-T286-CamKII and P-S9-Synapsin, which correlated with decreased synaptic vesicle recycling. Moreover, systemic administration of A1R antagonist counteracted the antidepressant-like actions of ketamine and (2R,6R)- HNK in the forced swim test.

Conclusions: By studying neuronally released glutamate, we identified a novel retrograde adenosinergic feedback mechanism that mediate inhibitory actions of ketamine on glutamate release that may contribute to its rapid antidepressant action.

Keywords: Ketamine, Glutamate, A1 adenosine Receptor, Antidepressant

Disclosure: Nothing to disclose.

P401. Neuronal Models of Circadian Rhythms in Major Depressive Disorder

Himanshu Mishra, Anusuya Arjavalingam, Krishna Vadodaria, Richard Weinshilboum, Fred Gage, David Welsh, Michael McCarthy*

University of California, San Diego, San Diego, California, United States

Background: Major depressive disorder (MDD) is a common and debilitating mental health condition that responds inconsistently to pharmacotherapy. Circadian rhythm abnormalities have been observed in patients with MDD including sleep and appetite disturbances and diurnal variation in mood. However, until recently, methods to study rhythms in live neurons from human subjects were not available and the mechanism underlying circadian rhythm disruption remains unknown.

Methods: We derived stem-cell lines from controls (N = 3) or MDD patients (N = 6) previously characterized for clinical response to escitalopram in a prospective clinical trial, choosing the best/worst responders to treatment out of a large cohort. Controls and patients were matched for demographic features. Using the embryoid body method, we derived TUJ1 + glutamatergic neurons from each donor. Circadian rhythms were examined in triplicate live cell cultures using a luminometer to measure rhythms over 7 days using the Per2-luc bioluminescent reporter. Rhythm parameters were calculated for each cell line (period, amplitude, phase). Analyses of variance (one-way ANOVA for case-control analyses or two-way ANOVA with repeated measures for time course studies) were used to determine statistical significance with p < 0.05.

Results: Compared to control neurons, Per2-luc rhythms in MDD neurons had a significantly shorter period under entrained conditions. Anti-depressant response correlated with lower amplitude rhythm in neurons from MDD patients whose symptoms did not remit on escitalopram. Compared to controls, MDD neurons had lower overall gene expression levels of CRY1 and PER2. Immunostaining revealed increased levels of BMAL1 in MDD neurons.

Conclusions: We conclude that neurons from MDD patients display abnormal period and dysregulated elements of the molecular clock. Overexpression of BMAL1 protein may lead to excess negative feedback of the molecular clock. Some of these differences may underlie differential outcomes in antidepressant treatment.

Keywords: Major Depression Disorder, Circadian Rhythm, Induced Pluripotent Stem Cells (iPSCs), Neuronal Stem Cells (NSCs)

Disclosure: Nothing to disclose.

P402. Sleep, Ketamine and Hyperarousal: Potential Influences on Suicidal Thoughts

Elizabeth Ballard*, Dede Greenstein, Nadia Hejazi, Wallace Duncan, Carlos Zarate

National Institute of Mental Health, Bethesda, Maryland, United States

Background: Ketamine, a glutamatergic modulator, is associated with rapid-reductions in both depressive symptoms and suicidal thoughts. A growing research literature has suggested that sleep difficulties represent a critical suicide risk factor. Previous work by our group has demonstrated that nocturnal wakefulness is associated with next-day suicidal thoughts and this relationship is normalized by ketamine administration; such that suicide ideation (SI) responders to ketamine demonstrate decreased nocturnal wakefulness the night after ketamine administration. More recently, our group demonstrated that oscillations in overnight beta power, as evaluated using a functional data analytic approach, are associated with next-day SI. This relationship between oscillations in beta power and SI may be indicative of a sleep-related hyperarousal process associated with suicide risk. However, the influence of ketamine on sleep-related hyperarousal more generally, and beta fluctuations more specifically, is undefined. The aim of this analysis was to evaluate the relationship of ketamine on sleep hyperarousal in a sample of unmedicated patients with treatment resistant depression (TRD). We then evaluated whether changes in these arousal-related processes mediate the SI response to ketamine.

Methods: 35 medication-free participants with TRD who participated in a double-blind placebo-controlled crossover trial of ketamine and completed overnight polysomnography (PSG) the nights before and after ketamine and placebo infusions were included in this analysis. For each participant, we calculated traditional PSG macroarchitecture metrics, including wake after sleep onset (WASO), total sleep time (TST), sleep efficiency (SE) and REM latency. Additionally, we estimated power spectral density (PSD) and averaged beta frequencies (18- 25 hz) in each 30-second epoch over 5 hours from sleep onset. We then used a functional data analytic approach to identify the three eigenfunctions or principal components (PCs) that represent the three primary orthogonal axes or latent patterns of variation evident in oscillatory patterns in beta power over time. To test the effect of drug (ketamine v placebo) on arousal measures, we used the macroarchitecture and PC scores as outcome measures in separate mixed effect models. To test our mediation hypothesis, we regressed SI on each drug*arousal measure interaction effect in separate models. All models controlled for period-specific baseline, age, infusion, and sex.

Results: In preliminary analyses, ketamine was associated with greater reductions in WASO relative to placebo (beta = -0.35, p = 0.03), but no drug effects were detected for TST, SE or REM latency. When PSG macroarchitecture metrics were limited to the 5 hours after sleep onset, the effect became a trend (p = .08) in the expected direction. None of the macroarchitecture arousal measures mediated ketamine’s effect on SI. After the removal of an outlier, ketamine was associated with lower scores on the second PC score, associated with oscillations of beta (beta = -0.37, p = 0.03). This sleep after ketamine administration was characterized by lower arousal shortly after sleep onset. Ketamine did not appear to be related to the first and third PCs which respectively reflected overall average levels of beta and declining beta over the course of the night. We did not find evidence to support temporal patterns of beta oscillations as mediators of ketamine’s therapeutic effect on SI.

Conclusions: Preliminary results indicate that ketamine may reduce arousal during sleep as measured by both WASO and temporal patterns of beta oscillations. Contrary to expectations, ketamine’s effect on SI was not mediated by arousal-related sleep metrics. We are pursing ongoing analysis of other frequency bands, including alpha and delta, to obtain a fuller picture of ketamine’s effects on sleep-related arousal.

Keywords: Suicide, Ketamine, Sleep, Polysomnography

Disclosure: Nothing to disclose.

P403. Reinforcement Learning and Prediction Error in Pediatric Irritability

Katharina Kircanski*, Diana Burk, Ellie Xu, Jennifer Meigs, Daniel Pine, Melissa Brotman, Bruno Averbeck, Ellen Leibenluft

National Institute of Mental Health, Bethesda, Maryland, United States

Background: Irritability is a common, chronic, and impairing clinical phenotype in youth (Leibenluft, 2011; Stringaris et al., 2018). Alterations in reward processing, including frustrative nonreward (i.e., omission of expected reward), are a proposed mechanism of pediatric irritability (Brotman et al., 2017; Leibenluft, 2017). While a handful of studies have examined reward processing in irritability (e.g., Adleman et al., 2011; Deveney, 2019; Dougherty et al., 2018), no studies have focused on reward prediction error (RPE) during reinforcement learning. RPE operationalizes the difference between an expected outcome and a received outcome; negative RPE (i.e., an outcome that is worse than expected) is posited to have particular relevance to frustrative nonreward and irritability (Kircanski et al., 2019). In the current study, we used a novel, child-friendly fMRI paradigm to assess reinforcement learning before and after a frustration induction in the scanner. We used computational methods to derive estimates of RPE during reinforcement learning and map them onto brain activation on a trial-by-trial basis, testing preliminary associations with irritability.

Methods: Data collection is ongoing; to date, the transdiagnostic sample includes 34 children and adolescents varying in level of irritability (M age = 13.9 years, SD = 2.4; 29% female; 14 with symptoms of disruptive mood dysregulation disorder [DMDD], 13 with attention deficit hyperactivity disorder [ADHD], 7 with no psychiatric disorder). The “Carnival” fMRI paradigm simulates games at a virtual carnival and comprises a series of probabilistic reinforcement learning tasks administered before and after a frustration block with rigged feedback. In each task block, participants learn to select between pairs of stimuli (2-armed bandit tasks; 80:20 reward ratio) to maximize monetary winnings, delivered via trial-by-trial feedback. Subjects use hand-held dynamometers to make selections, measuring motor force and arousal as clinically relevant to irritability. Halfway through the paradigm, unbeknownst to participants, a separate, rigged game occurs to induce frustration. Participants are debriefed after the task. Irritability is assessed using the parent-reported Affective Reactivity Index (ARI; Stringaris et al., 2012). For data analysis, a Rescorla-Wagner reinforcement learning model with two parameters (learning rate and inverse temperature) was fit to participants’ choice data. Subject-specific, trial-by-trial RPE estimates were extracted and used in whole-brain and ROI-based amplitude modulation analyses (AFNI) to examine modulation of brain activity by RPE and associations of this modulation with irritability (voxel-wise threshold p < .005, clusters>27 voxels [422 mm3]).

Results: The in-scanner frustration induction was successful; frustration ratings were higher during the rigged game than during both the pre- and post-frustration games (Fquadratic[1,33]=14.77, p = .001), with a large effect size (partial η2 = .31). With respect to task effects, as expected, a general linear test indicated significant modulation of regional activity by RPE, including large clusters of positive RPE encoding in the striatum and OFC, and of negative RPE encoding in the bilateral insula and dorsal anterior cingulate cortex (all ps < .005, whole-brain corrected). In the whole-brain analysis, there were no significant associations between RPE modulation and irritability. However, for a priori anatomical ROIs in the bilateral insula and striatum, activity as modulated by RPE was correlated with irritability. Consistent small-to-medium effect sizes were shown for correlations between parent-reported ARI and activity in the insula and striatum post-frustration (r range = -.25 to -.17). The insula associations were in the hypothesized direction, in which higher irritability was associated with enhanced negative RPE encoding. There were no directional predictions for the striatum, but preliminary associations suggested that higher irritability is associated with diminished positive RPE encoding.

Conclusions: These preliminary findings support the feasibility and utility of computational methods for examining RPE during reinforcement learning as a function of irritability and frustration, bridging the reward processing and FNR literatures (Yu et al., 2014). Whole-brain analyses supported robust task effects for RPE modulation in neural circuitry known to be engaged in reinforcement learning. Further, ROI analyses suggested small-to-medium effect sizes for hypothesized associations between irritability and enhanced negative RPE encoding in the insula. Data collection is ongoing; subsequent analyses will use the established pipeline in a sample optimized for statistical power (projected N = 120).

Keywords: Functional MRI (fMRI), Pediatric Irritability, Frustrative Non-Reward, Reinforcement Learning, Reward Prediction Error

Disclosure: Nothing to disclose.

P404. Lack of Association Between Pretreatment Glutamate/GABA and Major Depressive Disorder Treatment Response

Feiyang Dai, Kenneth Wengler, Xiang He, Junying Wang, Jie Yang, Ramin Parsey, Christine DeLorenzo*

Stony Brook University, Stony Brook, New York, United States

Background: Studies have shown gamma-amino-butyric acid (GABA) and Glx (a combination of glutamate and glutamine) to be altered in major depressive disorder (MDD). Using proton Magnetic Resonance Spectroscopy (1H-MRS), this study aimed to determine whether lower pretreatment GABA and Glx levels in the anterior cingulate cortex (ACC), a region implicated in MDD pathophysiology, are associated with better antidepressant treatment response.

Methods: Participants with MDD (N = 73) were antidepressant naïve or medication-free for at least three weeks before imaging. Two MEGA-PRESS 1H-MRS acquisitions were collected in the ACC, interleaved with a water unsuppressed reference scan. GABA and Glx concentrations were quantified from an average difference spectrum. Following imaging, participants were randomized to escitalopram or placebo for 8 weeks in a double-blind design. Multivariable logistic regression models were applied with treatment type and age as covariates. Bayes Factor hypothesis testing was used to interpret the strength of the finding.

Results: There was no significant association between pretreatment Glx, GABA, or Glx/GABA and remitter status or the continuous outcome, percent change in depression severity. In an exploratory analysis, no significant correlation was found between pretreatment Glx, GABA or Glx/GABA and days to response. Bayes factor analysis showed strong evidence towards the null hypotheses in all cases.

Conclusions: To date, there are no replicated biomarkers in psychiatry. To address this, well-powered, placebo-controlled trials need to be undertaken and reported. The present analysis

suggests GABA, Glx, or their ratio cannot predict antidepressant treatment response.

Keywords: Glutamate GABA, Depression, Magnetic Resonance Spectroscopy

Disclosure: Nothing to disclose.

P405. Prophylactic Effects of (R)-Ketamine on Schizophrenia-Relevant Phenotypes in Adult Offspring After Maternal Immune Activation: A Role of TRKB Signaling

Yunfei Tan, Yuko Fujita, Yaoyu Pu, Lijia Chang, Youge Qu, Xingming Wang, Kenji Hashimoto*

Chiba University Center for Forensic Mental Health, Chiba, Japan

Background: A number of studies demonstrated that maternal immune activation (MIA) might play a role in the development of neuropsychiatric disorders such as schizophrenia and autism spectrum disorder in offspring. It is demonstrated that pregnant mice exposed to polyinosinic:polycytidylic acid [poly(I:C)] resulted in schizophrenia-like behavioral and neurochemical abnormalities in their offspring.

We demonstrated that (R)-ketamine, (R)-enantiomer of the N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine, would be a novel rapid-acting and sustained antidepressant without side effects of ketamine (reviews by Hashimoto K. Biochem. Pharmacol. 2020; Wei Y, et al. Mol. Psychiatry 2021). Recently, we reported that phencyclidine (PCP)-induced cognitive deficits in mice could be ameliorated after subsequent repeated intermittent administration of (R)-ketamine, but not (S)-ketamine, and that brain-derived neurotrophic factor (BDNF)-TrkB signaling plays a role in the beneficial effects of (R)-ketamine in PCP model of schizophrenia (Tan Y, et al. Pharmacol. Biochem. Behav. 2020). Clinical study of (R)-ketamine in depressed patients is underway.

In this study, we examined whether repeated intermittent administration of (R)-ketamine during juvenile and adolescent stage ameliorates abnormal behavior, parvalbumin (PV)-immunoreactivity and dendritic spine density in the adult offspring after MIA.

Methods: Pregnant female mice ddY (5 days) were purchased from SLC Company Japan (Hamamatsu, Shizuoka Prefecture, Japan). From E12 to E17, every 6 consecutive days, the pregnant mice were intraperitoneally injected with Poly(I:C) (5.0 mg/kg/day), dissolved in 0.2 ml physiological saline, per 20 g body weight or an equivalent volume of physiological saline (Han M, et al. Sci. Rep. 2016; Fujita Y, et al. Sci. Rep. 2016; Matsuura A, et al, Sci. Rep. 2018). After 3 weeks, the offspring were separated from their mother mice, and male mice were kept in cages in groups of three to five. Saline (10 ml/kg/d, twice a week, for 4 weeks) or (R)-ketamine (10 mg/kg as hydrochloride salt, twice a week, for 4 weeks) was intermittent intraperitoneal injection (i.p.) into the mice from 4-weeks old to 8-weeks old. In the experiment using TrkB inhibitor, the vehicle or ANA-12 (0.5 mg/kg; TrkB inhibitor) was injected 30 minutes before saline (10 ml/kg) or (R)-ketamine (10 mg/kg). Novel object recognition test (NORT), PV-immunohistochemistry, and Golgi staining were performed as previously reported (Han M, et al. Sci. Rep. 2016; Matsuura A, et al, Sci. Rep. 2017; Zhang J, et al. Int. J. Neuropsychopharmacol. 2019). The data shown are the mean ± standard error of the mean (S.E.M.). Data were analyzed using one-way analysis of variance (ANOVA), followed post-hoc Tukey test.

Results: In the NORT, administration of poly(I:C) caused cognitive deficits in adult offspring. In the training session, there was no difference among the three groups. In the retention test, the repeated intermittent administration of (R)-ketamine significantly ameliorated the decreased exploratory preference in adult offspring after MIA. PV-immunohistochemistry showed that PV-immunoreactivity in the PrL of medial prefrontal cortex (mPFC) of poly(I:C) + vehicle group was significantly lower than that of vehicle + vehicle group or poly(I:C) + (R)-ketamine group. Furthermore, Golgi staining showed that dendritic spine density in the PrL of mPFC from poly(I:C) + vehicle group was significantly lower than that of vehicle + vehicle group or poly(I:C) + (R)-ketamine group.

Pretreatment with ANA-12 significantly antagonized the prophylactic effects of (R)-ketamine in the adult offspring of prenatal mice exposed to poly(I:C). In contrast, ANA-12 alone did not improve MIA-induced cognitive deficits.

Conclusions: The current data suggest that repeated intermittent administration of (R)-ketamine during juvenile and adolescent stages could prevent the onset of behavioral abnormalities, the reduction of PV-immunoreactivity and dendritic spine density in the mPFC of adult offspring after MIA. Therefore, treatment with (R)-ketamine in young subjects at high risk for psychosis may prevent conversion to psychosis.

Keywords: R-(-)-Ketamine, Ketamine, Maternal Immune Activation, Child Offspring, Schizophrenia-Like Behavior

Disclosure: Taisho, Dainippon Sumitomo, Otsuka,: Contracted Research (Self)

Perception Neuroscience: Grant (Self)

Patents: Patent (Self)

P406. Baseline Memory Function Affects Memory Outcome in Older Adults With Major Depressive Disorder Treated With Acute Course Electroconvulsive Therapy and Venlafaxine

Shawn McClintock*, Allison Gregg, Charles Kellner, C. Munro Cullum, Jayme Palka, Rebecca Knapp, Mary Dooley, Martina Mueller, Abeba Teklehaimanot, Richard Weiner, Elisabeth Bernhardt, Georgios Petrides, Mustafa Husain, W. Vaughn McCall, Robert Young, Joan Prudic, Peter Rosenquist, Sarah Lisanby

University of Texas Southwestern Medical Center, Dallas, Texas, United States

Background: Major depressive disorder (MDD) is a significant public health challenge worldwide. Major depression in the older adult populations worsens overall health, results in functional impairment, and leads to increased morbidity, and mortality. Moreover, depression in older adults tends to be treatment-resistant. For such treatment-resistant depression, and in acute crises cases such as the presence of suicidality and psychotic features, electroconvulsive therapy (ECT) is often prescribed. While ECT is highly beneficial in older adults with depression, it can also produce adverse cognitive effects. We previously assessed broad neurocognitive and specific verbal learning and memory component effects of a combined regimen of ECT and venlafaxine in older adults with depression during Phase 1 of the Prolonging Remission in Depressed Elderly (PRIDE) study. Prior research and our findings demonstrated that ECT adversely impacts multiple neurocognitive functions including verbal learning and memory. However, there is limited information regarding how baseline memory function relates to memory outcomes following treatment with ECT. The purpose of this analysis was to examine how baseline cognitive function, specifically verbal memory, affected ECT-associated memory outcome. We explored whether, following acute treatment with a regimen of ECT and venlafaxine, older adults with relatively intact baseline memory function would retain stable memory performance better than those with impaired baseline memory.

Methods: The PRIDE study was a NIMH funded, multicenter, randomized study of an individualized continuation ECT schedule combined with pharmacotherapy to enhance long-term outcomes in older adults with MDD. In Phase 1 of the study, patients received acute ECT thrice weekly combined with venlafaxine. ECT parameters were standardized as: right unilateral (RUL) electrode placement using a Somatics Thymatron System IV with an ultrabrief pulse width of 0.25ms and current of 0.9Amps or a MECTA SPECTRUM device with an ultrabrief pulse width of 0.3ms and current of 0.8Amps. Older adults (age > 60) with MDD were included. All participants provided written informed consent for this IRB approved investigation before completing study procedures. For the purposes of this analysis, the neurocognitive outcome data were collected with the 2nd edition of the California Verbal Learning Test (CVLT-II). The CVLT-II is a psychometrically sound measure of verbal learning and memory. The CVLT-II Standard and Alternate forms were used in order to minimize practice effects, with form order counterbalanced across study sites, subjects, and the two study time points (baseline, end) by a computerized algorithm. The CVLT-II was administered at Phase 1 baseline and within 72 hours following the last ECT session. CVLT-II raw scores were converted into demographic-adjusted scores. Based on baseline performance using the demographic-adjusted scores, the study cohort was characterized as having strong (z-score > 0.5), average (z-score > -0.5 and < 0.5), or impaired (z-score < -1) memory performance. Descriptive statistics were used to characterize the demographic, memory function, and clinical features of the sample, as well as the impact on memory performance following treatment. Percentages may not add up to 100% due to missing data.

Results: The study sample (n = 203) had a mean age of 69.9 (SD = 7.6), 14.5 (SD = 3.3) years of education, 57.5% were female and 95% were Caucasian. Verbal memory scores at baseline revealed that 32.1% showed strong performance, 35.4% showed average performance, and 32.5% showed impaired performance. Following acute treatment with RUL ultrabrief pulse ECT and venlafaxine, the three memory function groups showed differential outcomes. For those with strong baseline verbal memory function, 56.9% remained strong, 23.1% had average performance, and 9.2% displayed impaired performance. For those with average baseline verbal memory function, 31.9% remained average, 36.1% showed strong performance, and 15.3% had impaired performance. For those with impaired baseline verbal memory function, 36.4% remained impaired, 43.9% showed intact performance, and 6.1% had strong performance.

Conclusions: To our knowledge, this is one of the first studies to examine how baseline verbal memory function relates to performance following treatment with ECT and venlafaxine in older adults with MDD. Those with average and strong baseline performance showed relative stability and limited impairment after treatment. While some older adults with impaired baseline performance showed intact or strong performance after treatment, approximately 33% remained impaired. As such, average and strong baseline memory function may be a protective factor and impaired baseline memory function may be a risk factor for ECT-associated effects on memory performance. These findings are consistent with other treatments with known adverse cognitive effects where baseline cognitive function has been found to moderate treatment-associated cognitive outcomes. These findings highlight the importance of collecting neurocognitive information in older adults with depression who receive ECT. As this study only focused on verbal memory function, future research is warranted to examine other aspects of cognitive function such as attention, executive function, and working memory to examine how such baseline function may impact outcomes after treatment.

Keywords: Electroconvulsive Therapy, Depression, Memory, Cognition, Older Adults

Disclosure: Pearson Assessment: Consultant (Self)

P407. Orally Administered Choline Analog 2-(4-((1-phenyl-1H-pyrazol-4-yl)methyl)piperazin-1-yl)ethan-1-ol Attenuates Pentylenetetrazol-Induced Seizure-Like Effect in Mice

Iara Barbosa Cabral, Ricardo Menegatti, Gustavo Rodrigues Pedrino, Carlos Henrique Xavier Custódio, Elson Alves Costa, James Fajemiroye*

Universidade Federal de Goias, Goiania, Brazil

Background: A transient and recurrent seizure often leads to a long-lasting behavioral change and low quality of life in epileptic patients. The roles of cholinergic and GABAergic neuronal projections in epileptic seizures inspire the synthesis of choline analog 2-(4-((1-phenyl-1H-pyrazol-4-yl)methyl)piperazin-1-yl)ethan-1-ol (LQFM032) through molecular hybridization of 4-(1-Phenyl-1h-pyrazol-4-ylmethyl)-piperazine-1-carboxylic acid ethyl ester. With the cholinergic and significant cytoprotective effects of LQFM032 in the previous studies, we hereby conduct a preliminary evaluation of its anti-seizure-like effect.

Methods: Acute oral administration of LQFM032 (5, 15 or 45 mg/kg), diazepam (DZP 5 mg/kg) or vehicle 10 ml/kg was carried out before the exposure of 4-week-old male and female Swiss mice [Weight = 28 ± 3 g; n = 6 (3 mice per sex) randomly distributed into five groups] to the sodium pentobarbital (50 mg/kg i.p)-induced barbiturate sleep, open field and pentylenetetrazol (PTZ 60 mg/kg i.p.) - induced convulsion. In a separate experimental session, mice were pretreated intraperitoneally with flumazenil 2 mg/kg (FLU; competitive antagonist of benzodiazepine site of the GABA-A receptor), atropine 10 mg/kg (ATR; nonselective muscarinic receptor antagonist), or vehicle before the oral administration of LQFM032, DZP or vehicle. The NIH Guidelines for the Care and Use of Laboratory Animals as approved by the Ethics Committee of the Federal University of Goiás (protocol number 104/08) were adhered to in all experimental procedures. Data were subjected to ANOVA followed by Dunnett’s s or Bonferroni’s post hoc tests and expressed as mean ± SEM (p < 0.05 was considered statistically significant).

Results: The oral administration of LQFM032 (15 and 45 mg/kg) and DZP 5 mg/kg potentiated barbiturate sleep [Sleep latency with F (4, 25) = 21.4, and sleep duration with F (4, 25) = 19.8, p < 0.05], thereby showing CNS depressant property without alterations in locomotor activities in the open field arena [Total crossing with F (4, 25) = = 5.9, and freezing time with F (4, 25) = 12.1, p > 0.05]. Like DZP 5 mg/kg, an increase in the time to the first PTZ-induced myoclonic jerk [Latency with F (4, 25) = 17.7, p < 0.05] and a reduction in the duration of seizure [F (4, 25) = 10.5, p < 0.05] suggest the attenuation of seizure-like behavior by LQFM032. The involvement of the benzodiazepine site and muscarinic receptor in the activities of LQFM032 was shown by the blockade of its antiseizure-like property following FLU and ATR pretreatments.

Conclusions: Together, LQFM032 reduced seizure-like behavioral manifestations that involve cholinergic and GABAergic systems. Further evaluation of the specific modulator, receptor, or circuit underlying this anti-seizure-like mechanism remains pertinent. Keywords

Keywords: Choline Analog, Convulsion-Like Model, Cholinergic System, Gabaergic System, LQFM032

Disclosure: Nothing to disclose.

P408. Opposing Roles of Mu Opioid Receptors in Dopamine D1 and D2 Expressing Neurons in Opioid Mediated Analgesia

Catherine Cahill*

UCLA, Los Angeles, California, United States

Background: There is extensive interaction between systems involved in pain processing and motivation systems, where the aberrant functioning of salience circuits likely contributes to chronic pain as well as increased susceptibility for opioid misuse and opioid use disorder. The mesolimbic circuitry also contributes to opioid analgesia where an injection of intra-striatal morphine alleviated nociceptive behaviors associated with the chemical irritant formalin. In this study we asked to what extent mu opioid receptors (MOR) in dopamine D1 and D2 receptor expressing neurons contribute to opioid analgesia and negative reinforcement.

Methods: We ablated MOR in dopamine receptor expressing neurons by breeding D1-cre, D2-cre and A2A-cre with MORloxP mice. Mice were subjected to chronic pain followed by conditioned place preference to oxycodone or were tested in an inflammatory pain model induced by formalin.

Results: Ablating MORs from D1 receptor expressing neurons significantly reduced oxycodone (3 mg/kg, i.p.) mediated analgesia in the formalin test, whereas deleting MOR from D2 or A2A receptor expressing neurons enhanced oxycodone mediated analgesia in this test. In contrast, ablation of MOR from any of these neurons had no effect on formalin-induced pain, but only modified the opioid-mediated analgesia. Separate cohorts of mice underwent conditioned place preference to oxycodone following either sham or induction of neuropathic pain via sciatic nerve constriction. Conditioning was conducted over 6 days counterbalancing for day and chamber. Oxycodone produced a greater preference score in pain animals than sham control groups. Deleting MORs from D1 receptor expressing neurons prevented place preference in both sham and neuropathic pain groups. Whereas deleting MOR from D2 and A2A receptor expressing neurons enhanced oxycodone induced place preference in pain animals.

Conclusions: These data demonstrate that MORs have opposing roles in dopamine receptor expressing neurons (likely striatal) on opioid mediated analgesia and negative reinforcement.

Keywords: Pain, Ventral Striatum, Prescription Opioids, Negative Reinforcement, Analgesia

Disclosure: Nothing to disclose.

P409. Association Between Lower Body Temperature and Increased Tau Pathology in Cognitively Normal Older Adults

Esther Blessing*, Ankit Parekh, Natalie Saba, Betensky Rebecca, Ludovic Debure, Tracy Butler, Andrew Varga, Indu Ayappa, David Rapoport, Mony de Leon, Thomas Wisniewski, Brian Lopresti, Ricardo Osorio

New York University School of Medicine, New York city, New York, United States

Background: Rodent model and in vitro studies suggest brain temperature has the potential to bidirectionally interact with tau pathology in Alzheimer’s Disease (AD): tau phosphorylation is robustly increased by small (<1°C) reductions in temperature within the human physiological range, and lower brain thermoregulatory areas may be among those first affected by AD pathology. Here, we evaluated the cross-sectional association between body temperature (Tb), as a proxy for brain temperature, and clinically accessible markers of tau pathology in cognitively normal older adults.

Methods: Tb was measured continuously over 48 hours with ingestible telemetry combined with a novel pre-processing algorithm. This period included 2 nights of nocturnal polysomnography to facilitate delineation of Tb–tau pathology relationships according to waking vs sleeping time intervals. Tau pathology was assessed with both soluble markers including plasma P-tau (P-tau 181) and cerebrospinal fluid (CSF) P-tau, both sampled the following day, and aggregated tau, namely neurofibrillary tangle (NFT) burden in early (I-III) Braak stage areas imaged with MR-PET using the [18F]MK-6240 radio tracer on average ~ one month later

Results: Plasma and CSF P-tau levels were highly correlated with one another and with tau tangle radio tracer uptake (NFT burden), p < 0.05 for all comparisons. Lower Tb (quantified by lower mean Tb and a greater proportion of time Tb was under 37.0°C) was associated with increased NFT burden and increased plasma and CSF P-tau levels, p < 0.05 all comparisons. For aggregated tau, lower Tb – tau pathology associations were seen during for Tb recorded during waking, but not during sleeping intervals.

Conclusions: Preliminary results suggest that lower body temperature in older adults may be associated with increased aggregated and soluble tau pathology.

Keywords: Temperature, Tau, Alzheimer’s, Circadian, Sleep

Disclosure: Nothing to disclose.

P410. Effects of Reproductive Experience on Cost-Benefit Decision Making in Females

Mojdeh Faraji*, Jennifer Bizon, Barry Setlow

University of Florida, Gainesville, Florida, United States

Background: After decades of neglect, a growing body of preclinical behavioral neuroscience research is including female subjects, with significant findings that underscore the importance of this inclusion. These efforts have largely neglected the variable of reproductive experience, however, in that almost all studies employ reproductively naïve animals. Notably, the majority of women undergo reproductive/maternal experience at some point in their lives, and pregnancy and childbirth are associated with alterations in risks of several psychiatric disorders. Research in rodents shows that maternal experience affects spatial learning and other aspects of hippocampal function. In contrast, there has been little investigation of how reproductive experience affects cost-benefit decision making, despite the relevance of this aspect of cognition for psychiatric disorders.

Methods: To begin to address the aforementioned issues, female Long-Evans rats (nulliparous, n = 8; parous, n = 8) were evaluated in tests of impulsive and risky decision making in standard operant chambers. Rats in the parous group were mated, gave birth, and nursed for 21 days until pup weaning, whereas rats in the nulliparous group were unmated. One week after pups were weaned (or at the equivalent time point in nulliparous rats), rats began behavioral testing. Rats were initially tested in a delay discounting (impulsive choice) task, in which they made discrete trial choices between a small immediate food reward and a large food reward delivered after a variable delay period ranging from 0 to 60 s. Next, in a risky decision-making task, rats made discrete trial choices between a small, “safe” food reward and a large food reward accompanied by variable probabilities of mild footshock punishment. To investigate effects of reproductive experience on food motivation, rats were tested on a progressive ratio schedule of reinforcement. Data from the decision-making tasks were analyzed via two-factor, repeated measures ANOVA (group x delay or probability of shock), whereas data from the progressive ratio task were analyzed via Welch’s t-test.

Results: On the delay discounting task, there was an interaction between group and delay duration (F(4,56) = 3.57, p < .05). Specifically, parous rats chose the large reward less frequently than nulliparous in the first block of trials when delays were absent, suggestive of a deficit in discrimination between the large and small rewards. On the risky decision-making task, there was an interaction between group and shock probability (F(4,56) = 2.73, p < .05); on this task, however, parous rats chose the large reward more frequently than nulliparous, suggestive of greater risk taking in this group. Data from the progressive ratio task revealed no differences between groups (p = 0.51), indicating that nulliparous and parous rats were comparably motivated to obtain the food reward.

Conclusions: Together, these results show distinct effects of reproductive experience on different forms of cost-benefit decision making in females and highlight reproductive status as a variable that may influence aspects of cognition relevant for psychiatric disorders. Future work will determine the contributions of different components of reproductive experience to these effects, and whether reproductive experience influences cost-benefit decision making in males as well.

Keywords: Reproduction, Decision Making, Rodent Models

Disclosure: Nothing to disclose.

P411. Intrathecal Inflammatory Responses in the Absence of SARS-CoV-2 Nucleic Acid in the CSF of COVID-19 Hospitalized Patients

Shibani Mukerji*, Erica Normadin, Kathryn Holroyd, Sarah I. Collens, Bennett M. Shaw, Katherine Siddle, Gordon Adams, Melissa Rudy, Issac H. Solomon, Melis N. Anahtar, Jacob E. Lemieux, Bianca A. Trombetta, Pia Kivisakk, Steven E. Arnold, Otto Rapalino, Anne L. Piantadosi, Pritha Sen, Eric S. Rosenberg, John Branda, Pardis C. Sabeti

Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts, United States

Background: Little is known about cerebrospinal fluid (CSF) profiles in patients with acute COVID-19 infection and neurological symptoms. Here, CSF was tested for SARS-CoV-2 RNA and inflammatory cytokines and chemokines and compared to controls and patients with known neurotropic pathogens.

Methods: CSF from twenty-seven consecutive patients with COVID-19 and neurological symptoms was assayed for SARS-CoV-2 RNA using quantitative reverse transcription PCR (RT-qPCR) and unbiased metagenomic sequencing. Assays for blood-brain barrier (BBB) breakdown (CSF: serum albumin ratio (Q-Alb)), and proinflammatory cytokines and chemokines (IL-6, IL-8, IL-15, IL-16, monocyte chemoattractant protein -1 (MCP-1) and monocyte inhibitory protein – 1β (MIP-1β)) were performed in 23 patients and compared to CSF from patients with HIV-1 (16 virally suppressed, 5 unsuppressed), West Nile virus (WNV) (n = 4) and 16 healthy controls (HC).

Results: The median CSF cell count for COVID-19 patients was 1 white blood cell/μL (range 0-7250); two patients were infected with a second pathogen (Neisseria, Cryptococcus neoformans). No CSF samples had detectable SARS-CoV-2 RNA by either detection method. In patients with COVID-19 only, CSF IL-6, IL-8, IL-15, and MIP-1β levels were higher than HC and suppressed HIV (corrected-p < 0.05). MCP-1 and MIP-1β levels were higher, while IL-6, IL-8, IL-15 were similar in COVID-19 compared to WNV patients. Q-Alb correlated with all proinflammatory markers, with IL-6, IL-8, and MIP-1β (r ≥ 0.6, p < 0.01) demonstrating the strongest associations.

Conclusions: The lack of SARS-CoV-2 RNA in CSF despite neurological symptoms is consistent with current literature on hospitalized COVID-19. Intrathecal proinflammatory cytokines and chemokines correlate with markers of BBB breakdown in a subset of patients despite minimal CSF pleocytosis and may explain some of the neurological sequelae in COVID-19.

Keywords: Neuroinfection, Pro-Inflammatory Cytokines, Novel Coronavirus (SARS-CoV-2), CSF Biomarkers, Next Generation Sequencing

Disclosure: Nothing to disclose.

P412. Identification of Plasma Biomarkers Involved in Regulation of Inflammatory Pain

Irma Cisneros*, Christina Merritt, Sonja Stutz, Obdulia Covarrubias, Konrad Pazdrak, Stefan Bossman, Massoud Motamedi, Kathryn Cunningham

University of Texas Medical Branch of Galveston, Galveston, Texas, United States

Background: Physicians are challenged in treating pain patients due to the lack of quantifiable, objective methods of measuring pain in the clinic; pain sensation is multifaceted and subjective to each individual. There is a critical need for point-of-care quantification of accessible biomarkers to provide objective analyses beyond the subjective pain scales currently employed in clinical care settings. In the present experiment, we employed an animal model to test the hypothesis that blood-born regulators of the inflammatory response directly associate with an objective behavioral response to inflammatory pain. Upon induction of localized paw inflammation, we measured various cytokines and matrix metalloproteinases (MMPs) that are known to participate in the inflammatory response and investigated their relationship to the behavioral response across a 24-hour period.

Methods: Male Sprague-Dawley rats (n = 6/group) outfitted with indwelling jugular catheters were injected with 0.1 ml of saline or 0.1 ml of the pro-inflammatory compound λ-carrageenan (1%) into the left hindpaw. Quantification of carrageenan-evoked paw inflammation (paw thickness) and locomotor activity, as well as collection of blood (500 µl) for later biochemical analyses occurred 24 hrs prior to intraplantar injection (baseline) and at four timepoints post-injection (1-24 hrs). Plasma was aliquoted from each sample for detection of cytokines (BioPlex Rat Cytokine Panel) and MMPs.

Results: Intraplantar injection with 1% λ-carrageenan induced a significant increase in paw thickness across 24 hrs, with peak inflammation observed at 8 hrs (p < 0.05 vs saline). Pearson’s correlation analyses revealed that locomotor activity counts negatively correlated with paw inflammation at 8 hrs (r2 = 0.5645, p < 0.05), demonstrating impaired locomotion at the peak of paw inflammation. Expression of the chemokines C-X-C motif chemokine ligand 1 (Gro KC) (r2 = 0.7061, p < 0.05) and monocyte chemoattractant protein-1 (MCP-1) (r2 = 0.5050, p < 0.05) positively correlated with paw inflammation and negatively correlated with locomotor activity at 8 hrs (Gro KC, r2 = 0.6386, p < 0.05; MCP-1, r2 = 0.4150, p < 0.05). The ratio of MMP9 to MMP2 activity negatively correlated with paw inflammation (r2 = 0.4759, p < 0.05) at 8 hrs. No relationship between MMP9/MMP2 activity and locomotor activity was observed this timepoint. Interestingly, a mixed model ANOVA of the time course of MMP9/MMP2 activity revealed a significant increase at 1 hr (p < 0.05 vs saline).

Conclusions: We postulate that the chemokines Gro KC and MCP-1 as well as the ratio of MMP9 to MMP2 activity may serve as predictive biomarkers for the timecourse of inflammation-associated behavioral deficits. These data define opportunities for the future development of a point-of-care device to objectively quantify biomarkers for inflammatory pain states.

Keywords: Inflammation, Pain Sensitivity, Immune Biomarkers

Disclosure: Nothing to disclose.

P413. Deep Brain Optical Imaging of Subcellular cAMP Signaling Dynamics During Striatum-Dependent Learned Behaviors

Shana Augustin*, Yolanda Mateo, Alexa Gracias, Rishitha Anumola, Jeong Lee, David Lovinger

NIH/NIAAA/Laboratory for Integrative Neuroscience, Rockville, Maryland, United States

Background: Striatal neuromodulators have critical roles in motor control, decision-making, and substance use disorders. These neuromodulators exert their functions through G-protein-coupled receptors (GPCRs) on striatal neurons that activate second messenger intracellular cascades to affect neuronal signaling. Understanding how neuromodulation involving intracellular signaling molecules can shape synaptic efficacy and circuit functions involved in decision making and behavior is critical to advancing our knowledge of basal ganglia function. The interaction of dopamine and the cAMP-PKA signaling pathway is important in the modulation of synaptic plasticity. The spatial and temporal changes of these striatal intracellular molecules during the induction of synaptic plasticity and behavior are unclear.

Methods: To study the subcellular cAMP dynamics in rodent brain slices and in vivo during behavior, we expressed adeno-associated virus expressing a genetically encoded fluorescent cAMP biosensor, cAMP Difference Detector in situ (cADDis) in a Cre recombinase dependent manner in male and female mice expressing Cre in D1 dopamine receptor-expressing (D1rda) and D2 receptor expressing (A2a) medium spiny neurons (MSNs). Fast-scan cyclic voltammetry and cADDis were used to simultaneously measure dopamine release and subsequent downstream GPCR-mediated cAMP-PKA signaling in striatal brain slices. To examine the relationship between postsynaptic cAMP-PKA activity and motor actions, we measured cAMP-PKA dynamics using fiber photometry during skill and procedural learning.

Results: MSN-cAMP transients can be altered by changes in stimulation duration and are blocked by tetrodotoxin, indicating that they are driven by neuronal activation. During afferent stimulation, MSN-cAMP signaling is primarily influenced by dopamine transmission and seems to be directly modulated by dopamine receptor activation measured with simultaneous recordings of dopamine and cAMP-PKA signaling. Specifically, single pulse electrical stimulation generates increased cAMP in D1 MSNs and decreased cAMP in D2 MSNs. Using fiber photometry and cADDis, we observed real-time movement- and trial-related changes in MSN-subcellular cAMP signaling during motor-skill learning on the accelerating rotarod. Similar changes in cAMP-PKA dynamics have been implicated in complex procedural learning, thus we are beginning to examine subcellular changes during goal-directed behaviors.

Conclusions: Our findings indicate the feasibility of using cADDis combined with traditional methods to investigate the precise temporal changes in striatal dopamine-cAMP signaling in real-time. My work aims to link changes in subcellular GPCR function to events relevant for behavior in vivo; thus, providing a causal link between neuronal signaling and behavior.

Keywords: Basal Ganglia, cAMP Signaling, Dopamine

Disclosure: Nothing to disclose.

P415. LYT-300: An Orally Bioavailable Prodrug of Allopregnanolone With Anticonvulsant Activity

Daniel Bonner*, Jamie Simpson, Rishab Shyam, Elvana Veizaj, Garry Qirici, Ingrid Rankin, Annie Guo, Raz Banosian, Sifei Han, Dan Zheng, Luojuan Hu, Natalie Trevaskis, Christopher J.H. Porter, Eric Elenko, Joe Bolen

PureTech Health, Boston, Massachusetts, United States

Background: Neuroactive steroids, which function as allosteric modulators of GABAA receptors, are in clinical development for post-partum depression, intractable epilepsy, tremor, status epilepticus, and some genetic epilepsy disorders. (3α,5α)-3-Hydroxy-pregnan-20-one (allopregnanolone or ALLO) is an endogenous neuroactive steroid which is a positive allosteric modulator of GABAA receptors. An intravenous formulation of allopregnanolone (brexanolone) was recently approved for treatment of severe postpartum depression (marketed as Zulresso®) where it is given in a hospital setting over a 60-hr infusion period. The duration of antidepressant effect has been reported out to 30 days.

The low oral bioavailability of allopregnanolone was the rationale underlying the development of an intravenous dosing formulation. The ability to provide ALLO at therapeutic drug levels by the oral route could have significant advantages and expand its applicability beyond postpartum depression (PPD).

Methods: A novel prodrug strategy was used to facilitate sufficient exposure of ALLO by leveraging lymphatic absorption of dietary lipids. PureTech Health’s Glyph technology reversibly connects an active drug to a dietary fat molecule, which shifts the route of intestinal absorption from the liver to the gut-draining lymphatics. Typically, molecules are absorbed into intestinal epithelial cells, passed to the liver and then into the systemic blood circulation. However, lipids and other highly lipid-soluble molecules are transported via the lymphatic route via a specific set of fat-processing pathways, bypassing the liver. The prodrug technology mimics this system by the reversible attachment of the drug to a triglyceride. This system uses proprietary chemistry to form the reversible attachment to the parent compound (ALLO). A self-immolative portion controls systemic release of the parent compound once absorbed, a linker tunes recognition for triglyceride resynthesis to maximize lymphatic transport levels, and a terminal glyceride integrates prodrug into chylomicrons for lymphatic transport. Using this approach, a series of prodrugs were synthesized and characterized in pharmacokinetic studies by oral dosing in various species. Male cynomolgus monkeys (n = 6) or beagle dogs (n = 4) were fed a standardized diet prior to drug administration. Compounds were formulated in gelatin capsules using a long-chain lipid-based self-emulsifying drug delivery system. Levels of free ALLO in plasma were determined by LC-MS/MS.

Behavioral observations (by blinded observers) of anticonvulsant activity were assessed to determine if LYT-300 could recapitulate the effects of ALLO. Experimental work using animals was under the approval and oversight of an institutional committee and veterinary staff. Male, albino CF-1 mice were used to study of the effects of orally-administered LYT-300 on anticonvulsant activity at multiple time points after LYT-300 dosing (n = 4 for each time point). The 6 Hz seizure model was used to detect compounds with novel mechanisms of action and potential activity against pharmacoresistant seizures and detects effects of ALLO.

Results: A series of lipid prodrugs of ALLO were synthesized and evaluated for their ability to provide systemic exposure in several species after oral administration. Plasma exposure of free allopregnanolone was observed after oral administration of lymphatic targeting prodrugs in both dogs and non-human primates. Apparent bioavailability of free allopregnanolone in the plasma from oral administration of prodrug versus IV administration of free ALLO was calculated to be over 30 percent in both species. Further studies in anesthetized rats supported the lymphatic mechanism of uptake. In these studies (n = 3), ALLO prodrug was found to be present in the mesenteric lymph following intraduodenal infusion of prodrug.

In the 6Hz seizure test, orally dosed LYT-300 was confirmed to have anti-convulsant activity. Pharmacokinetic analysis of ALLO levels in the mice in the 6Hz assay showed significant, dose-dependent exposure.

Conclusions: LYT-300, when given orally to a range of species, provides significant release of parent compound, allopregnanolone (ALLO). In mice, oral administration of LYT-300 produced dose-dependent increases in plasma exposure of ALLO and evidence of anticonvulsant efficacy. These data provide proof of concept that LYT-300 (p.o.) can deliver the pharmacologically active compound ALLO at levels that produce ALLO-related pharmacological effects. An orally-bioavailable ALLO is likely to be a major advance in therapeutics for wide-ranging neuropsychiatric disorders. A Phase 1 clinical trial in healthy volunteers is expected to begin in 2021 to characterize the safety, tolerability, and pharmacokinetics of orally administered LYT-300. This study may include exploratory endpoints such as beta wave power electroencephalography, a marker of GABAA receptor target engagement.

Keywords: GABA-A, Positive Allosteric Modulator, MDD, GABA-A, Positive Allosteric Modulators, GABAA Receptor Positive Allosteric Modulator, Epilepsy, Mood

Disclosure: PureTech Health: Employee (Self)

P416. The Role of Male-Specific Perinatal Sex Hormones in the Development of Sex-Biased Social Behavioral Dysregulation

Evan Bordt*, Haley Norris, Christopher McDougle, Staci Bilbo

Massachusetts General Hospital, Charlestown, Massachusetts, United States

Background: Immune alterations such as aberrant activation of microglia, the innate immune cells of the brain, are described in patients with neurodevelopmental disorders (NDDs). Our lab has demonstrated that microglia from male rodents play a critical role in the development of neural circuits underlying social behavior through selective phagocytosis of synapses in male but not female rodents. Microglial homeostatic and inflammatory processes are intimately linked to mitochondrial function, and mitochondrial abnormalities have also been reported in early-onset NDDs, suggesting that microglial mitochondria play a role in brain vulnerabilities underlying NDD risk. The incidence of early-onset neurodevelopmental disorders such as Autism Spectrum Disorder is strongly male biased. One well-characterized sex-specific developmental program that may underlie this male-biased incidence is a surge of gonadal hormones that occurs only in males during a perinatal critical period of brain development. This surge of gonadal hormones masculinizes the male body and brain. Importantly, we can divert the female brain towards a male-like state by injecting female mouse pups during this perinatal critical period with estradiol, the aromatized form of testosterone that has been shown to masculinize the male brain. This allows us to determine whether gonadal sex hormones impart male-typical vulnerability independent of the chromosomal milieu. Here, we hypothesized that gonadal sex hormones during a perinatal critical period of brain development induce vulnerability to immune alterations in male microglia that lead to impaired brain development and aberrant social behavior.

Methods: Perinatal immune challenge of male, female, and masculinized female mice was performed at postnatal day (PN) 9. Mice were subcutaneously injected with 10 mg/kg lipopolysaccharide (LPS) or vehicle saline. Wild type mice or mice lacking toll like receptor 4 (TLR4), a receptor recognizing LPS, specifically in microglia (Cx3cr1-CreBT:TLR4flox/flox (TLR4 cKO)) were used to study effects of perinatal immune challenge on social behavior, microglial function, and mitochondrial function. For masculinization studies, a subset of female mice were masculinized by subcutaneous injection on postnatal days (PN) 0 and PN1 with 100 ug estradiol benzoate dissolved in sterile sesame seed oil. Mice underwent 3-chambered sociability and social novelty preference testing starting at PN30. A cohort of mice were sacrificed on PN30 for molecular and immunohistochemical assays. Microglia were isolated from prefrontal cortex using positive bead selection. Mitochondrial gene expression was assessed by PCR array. Microglial cellular oxygen consumption was determined using MitoXpress Oxygen Consumption Assay. Immunostaining for mitochondria within microglia and astrocytes was performed, and cellular mitochondrial morphologies (mitochondrial length, volume, and network connectivity) were assessed using Fiji and Imaris volumetric reconstructions. N = 6-12 per group for social behavior experiments, 3-4 per group for PCR array experiments, and 3-8 per group for imaging experiments. Two-way ANOVAs (sex x treatment) followed by Bonferroni’s post-hoc analyses were performed to determine significance.

Results: PN9 LPS challenge induced male-specific deficits in sociability and social novelty preference (p < 0.0001) that were prevented by microglia-specific ablation of TLR4 signaling (TLR4 cKO mice do not show sociability deficits in response to LPS; p > 0.99). Masculinizing female pups at birth induced male-typical vulnerability to immune challenge-induced social deficits (p < 0.0001). Microglia isolated from the prefrontal cortex of PN30 male and masculinized female mice injected at PN9 with LPS demonstrated significantly downregulated expression of 54% of mitochondrial electron transport chain (mtETC) genes, whereas this same challenge did not alter female mtETC gene expression. PN9 LPS challenge also induced significant decreases in microglial mitochondrial length, volume, and network connectivity measures in male and masculinized female, but not in female, mice (p < 0.05).

Conclusions: These findings suggest that there are sex differences in social behavior and microglial mitochondria function that are dependent upon both microglial inflammatory signaling as well as the organizational perinatal sex hormone surge. We are currently exploring the mechanisms through which perinatal sex hormones induce this sex-specific vulnerability to perinatal immune challenge.

Keywords: Microglia, Mitochondria, Sex Hormones, Brain Development, Neuroimmunology

Disclosure: Nothing to disclose.

P417. A Female-Specific Role of RGS20 in Transcriptional, Epigenomic and Behavioral Responses to Chronic Pain

Anne Ruiz*, Sevasti Gaspari, Kerri Pryce, Lorna Farrelly, Dipanwita Pati, Aarthi Ramakrishnan, Claire Polizu, Natarajan Bhanu, Benjamin Garcia, Barbara Guarez, Erin Calipari, Thomas Kash, Li Shen, Ian Maze, Venetia Zachariou

Icahn School of Medicine at Mount Sinai, New York, New York, United States

Background: The signal transduction protein named Regulator of G-protein Signaling-20 (RGS20) modulates functional responses of several GPCRs in the brain, by acting as a GTPase activator or as an effector antagonist for G□ subunits. It is found highly expressed in the periaqueductal gray (PAG), a key component of the descending pain pathway. Using genetic mouse models, genomic and proteomic approaches we are studying the female-specific role of RGS20 in sensory hypersensitivity associated with chronic pain states.

Methods: Constitutive knockout of RGS20 (RGS20KO), as well as conditional knockdown of RGS20 in the mouse PAG were used along with RGS20WT animals.

Peripheral inflammation was induced by intraplantar injection of Complete Freud’s adjuvant (CFA)) and chronic pain by spared nerve ligation (SNI). Mechanical allodynia and thermal hyperalgesia were measured using Von Frey and Hargreaves respectively.

Following 3 or 10 days after CFA injection in the hind paw, PAGs were collected. RGS20 expression was verified by qPCR and western blot. To better understand the underlying sex specific mechanisms we utilized ChIP-qPCR on female PAG with the estrogen receptors alpha (Esr1) and beta (Esr2), and we measured Esr1 and Esr2 protein levels by western blot. We also performed RNA-sequencing on male and female PAG and identified candidate genes using IPA (QIAGEN) and validated them by qPCR. Fast-Scan Cyclic Voltammetry was used to measure changes of serotonin PAG projections following CFA injection and neuronal activity was monitored by whole-cell patch clamp. Finally, bottom-up mass-spectometry was used to study histone mark changes across all conditions and the mark of interest was chosen was chosen to pursue with ChIP-sequencing.

Results: Both RGS20KO and conditional knockdown of RGS20 in the PAG, exacerbate mechanical allodynia and thermal hyperalgesia in models of peripheral inflammation and nerve injury in female but not male mice. Furthermore, we show that prevention of RGS20 action delays recovery from thermal hypersensitivity in female mice after CFA treatment. In PAG tissue, biochemical studies revealed a sex-specific upregulation of RGS20 levels three days after the induction of peripheral inflammation. Chromatin Immunoprecipitation (ChIP)-qPCR at this time point reveals there is no change in ER elements binding to the RGS20 promoter. RNA Sequencing analysis of PAG samples from RGS20WT and RGS20KO mice under naïve states or 10 days after CFA, uncovered that exacerbated sensory hypersensitivity upon RGS20 knockdown is associated with changes in the expression of genes and pathways associated with central sensitization and pain maintenance, including molecules involved in serotonin synthesis and release. This was confirmed by voltammetry where stimulated release and readily releasable pool were increased in the rostral ventromedial medulla of RGS20WT following CFA injection, but this effect was significantly diminished in RGS20KO. Whole cell patch clamp recordings from rostral ventromedial medulla neurons also reveal decreased activity in CFA RGS20KO groups compared to RGS20WT mice. Proteomic analysis of epigenetic marks in the female PAG, identified that following CFA treatment, H3K14ac was increased in RGS20WT and decreased in RGS20KO animals. On the contrary, H3K9me2/H3K14ac expression decreased following CFA treatment in RGS20WT animals, and decreased in naïve RGS20KO animals vs RGS20WT. Ongoing ChIP-seq analysis of the selected histone marks is expected to provide details on key genes affected by dysregulation of RGS20.

Conclusions: Our studies highlight a novel female-specific intracellular pathway in the PAG which controls the severity of sensory hypersensitivity and recovery from chronic pain states.

Keywords: Chronic Pain, GPCR, Sex-Specific

Disclosure: Nothing to disclose.

P418. Resting-State Individual Variability in Youth and Young Adults With Autism Spectrum Disorder: Insights From a Transcranial Magnetic Stimulation Trial

Iska Moxon-Emre*, Zafiris J. Daskalakis, Daniel M. Blumberger, Paul E. Croarkin, Vinh Tan, Colin Hawco, Erin W. Dickie, Lindsay D. Oliver, Rachael E. Lyon, Meng-Chuan Lai, Pushpal Desarkar, Peter Szatmari, Stephanie H. Ameis

The Centre for Addiction and Mental Health, Toronto, Canada

Background: Individuals with autism spectrum disorder (ASD) exhibit greater variability of resting-state functional connectivity than typically developing controls (TDC). Recent work also suggests that fronto-parietal network engagement during a spatial working memory (SWM) task is more variable in ASD vs. TDC. Repetitive Transcranial Magnetic Stimulation (rTMS) is a neuromodulatory intervention, wherein brain variability among targeted networks may influence optimal network engagement. We used two approaches to characterize individual variability of resting-state connectivity in youth and young adults with ASD, and examined the effect of a 4-week (20-session) clinical trial of active vs. sham rTMS to the dorsolateral prefrontal cortex (DLPFC). Our primary objective was to evaluate if variability metrics change following rTMS intervention. We also explored whether change in variability from pre-to-post rTMS correlates with improved SWM task performance.

Methods: Resting state fMRI was acquired in 37 ASD participants [22.8 (4.55) years; 12-female] pre and post-rTMS, and in 20 TDC participants [23.9 (4.34) years; 6-female] at a single time-point (baseline). Mean correlational distance, a similarity/difference metric that captures the pattern of functional connectivity between the rTMS stimulation site (8mm region of interest, L/R-DLPFC) and the remainder of the brain, was calculated between each pair of participants from the active and sham groups separately (so as to assess change in variability among those exposed to the same treatment). Distance metrics derived from Personalized Intrinsic Network Topography (PINT) were used to measure variability in spatial locations of fronto-parietal resting-state network nodes. SWM was assessed with the Cambridge Neuropsychological Test Automated Battery (CANTAB). All variability metrics were compared between ASD and TDC groups at baseline using ANCOVAs. PINT-derived distances were compared from pre-to-post rTMS between the active vs. sham ASD groups, whereas mean correlational distance and SWM task performance were examined from pre-to-post rTMS in the active and sham group separately, using linear mixed models. Age and framewise displacement (for variability analyses) were included as covariates.

Results: ASD and TDC groups did not differ in either variability metric at baseline. PINT distances did not differ from pre-to-post rTMS in either treatment group, though frontal nodes were more variable than parietal or temporal network nodes, across all participants and treatment groups (all p < 0.05). Mean correlational distance of R-DLPFC functional connectivity changed from pre-to-post rTMS in both the active (F(1,15) = 5.04, p = 0.04), and sham (F(1,18) = 28.54, p < 0.001) ASD groups; participants in the active group became less variable, and those in the sham group became more variable (this pattern of change was consistent for L-DLPFC, despite no significant change from pre-to-post rTMS in either group). Although improved SWM performance from pre-to-post rTMS did not reach statistical significance in the active group (F(1.16) = 3.6, p = 0.07), change in mean correlational distance (L-DLPFC) from pre-to-post rTMS was positively correlated with change in SWM performance (r = 0.53, p = 0.03); participants in the active group who became less variable post-rTMS exhibited the greatest improvements in SWM performance.

Conclusions: Our results suggest that active rTMS may reduce/limit variability of functional connectivity, with the DLPFC, in ASD. Moreover, it is promising that we found a relationship between variability of L-DLPFC functional connectivity and SWM performance in participants treated with active rTMS. Given that rTMS was delivered to the DLPFC, and that we found frontal network ROIs to be most variable, it may be critical to account for variability, whether pre-emptively prior to rTMS delivery, or when relating measures of brain activation to behavioral and clinical outcomes following rTMS.

Keywords: Autism Spectrum Disorder, Repetitive Transcranial Magnetic Stimulation (rTMS), Clinical Trial, Functional MRI (fMRI), Individual Variability

Disclosure: Nothing to disclose.

P419. SARS-CoV-2 Acutely Infects Sensory Nervous System Tissue and Triggers an Injury Response Underlying Hypersensitivity in a Hamster Respiratory Infection Model

Randal Serafini*, Justin Frere, Jeffrey Zimering, Kerri Pryce, Anne Ruiz, Benjamin tenOever, Venetia Zachariou

Icahn School of Medicine at Mount Sinai, New York, New York, United States

Background: COVID-19 results in variable sensory symptoms in a notable percentage of the patient population, including headache, myalgias, and nerve pain. Understanding the mechanisms underlying these symptoms in sensory structures such as dorsal root ganglia (DRGs) and spinal cord (SC) can help identify treatments for acute and prolonged somatosensory COVID-19 symptoms and potentially highlight novel pain pathways.

Methods: Male golden hamsters received 1000 plaque-forming units of intranasal SARS-CoV-2 or saline. Cervical and thoracic dorsal root ganglia (DRGs) and spinal cord (SC) were harvested at 1-, 4-, 7-, and 14-days post-infection (dpi). Real-time PCR and RNAscope were used to validate DRG and SC infection and measure SARS-CoV-2 co-receptor expression. Bulk RNA sequencing was used to identify infection-related maladaptive pathways. Existing DRG RNA sequencing data from spared nerve injury (SNI) and complete Freund’s adjuvant (CFA) models was meta-analyzed against our SARS-CoV-2 DRG sequencing data. The Von Frey assay was used to assess mechanical hypersensitivity. N = 4-8 hamsters were used per experiment in this study. T-tests, one-way and two-way ANOVAs were used for molecular and behavioral analyses. DESeq2 was used for differential gene expression list generation for bulk RNA sequencing experiments.

Results: SARS-CoV-2 spike and nucleocapsid RNA was detected in cervical and thoracic DRGs and SC at 1dpi, but subsided in almost all samples by 4dpi except for thoracic SC (RM two-way ANOVA, p < 0.05). Interestingly, Tmprss2 co-receptor expression was upregulated in mock thoracic versus cervical SC (t-test, p = 0.017), suggesting vulnerability to prolonged infection at this SC level. 894 upregulated and 136 downregulated genes were identified in 3dpi combined cervical/thoracic SARS-CoV-2 DRGs compared to saline (log2(FC) > | 0.5 | , p-adj<0.05). Top canonical pathways associated with these changes included: Opioid Signaling Pathway (-log(p) = 6.362), Synaptogenesis Signaling Pathway (-log(p) = 5.259), Axonal Guidance Signaling (-log(p) = 5.053), and GABA Receptor Signaling (-log(p) = 4.863) (Qiagen IPA). Meta-analysis between SARS-CoV-2 and CFA revealed 68 commonly upregulated genes associated with interferon response and extracellular matrix reorganization. Similar pathways were commonly upregulated between SARS-CoV-2 and SNI (79 genes), although 161 genes were contra-regulated. The opposing gene set suggests upregulated sodium channel activity and synaptic plasticity pathways in DRGs from SARS-CoV-2-infected hamsters that are downregulated in SNI. Von Frey revealed mechanical hypersensitivity in SARS-CoV-2 hamsters at 4dpi (one-way ANOVA, p = 0.013; Tukey’s m.c., p = 0.012).

Conclusions: SARS-CoV-2 actively infects DRGs and the SC in the golden hamster model of COVID-19. Infection-related transcriptomic maladaptations reflect molecular signatures seen in peripheral neuropathy models, which is demonstrated by mechanical hypersensitivity in hamsters. However, unique transcriptional changes induced by SARS-CoV-2 infection of the DRG could point to novel pain pathways. Future work will focus on SARS-CoV-2-induced, sustained peripheral neuropathy signatures and the contribution of prolonged sensory perturbations to long-term affective components of COVID-19, a phenomenon commonly experienced by chronic pain patients.

Keywords: Novel Coronavirus (SARS-CoV-2), Sensory Processing, Dorsal Root Ganglia, Spinal Cord, Tissue Transcriptomics

Disclosure: Nothing to disclose.

P420. Efforts to Accelerate Development of Non-Opioid, Non-Addictive Pain Therapeutics Within the NIH Heal Initiative Preclinical Screening Platform for Pain: Validating Two Models of Chemotherapy-Induced Painful Neuropathy in the Rat

Mark Varney*, Smriti Iyengar, Sarah Woller, Elizabeth Dugan, Katelyn Buban, Jennifer Hagedorn, Philip Wig, Emer Leahy, Mark Urban

PsychoGenics, Inc., Paramus, New Jersey, United States

Background: With the goal of accelerating the discovery and development of new non-opioid, non-addictive pain therapeutics, the National Institutes of Health Helping to End Addiction Long-term Initiative, or NIH HEAL Initiative, Preclinical Screening Platform for Pain (PSPP) program PSPP is collaborating with PsychoGenics, Inc. to validate preclinical models and endpoints to enable screening and profiling of assets. Here, we describe the validation and optimization of the paclitaxel and oxaliplatin models of chemotherapy-induced peripheral neuropathy in the rat. Repeated dosing of the chemotherapeutic agents paclitaxel or oxaliplatin in rats has been shown to produce hind paw hypersensitivity to tactile and cold stimuli, and these effects are believed to resemble sensory neuropathy observed in the clinic.

Methods: Adult male and female Sprague Dawley rats (N = 10, each sex) were used in these studies. For the paclitaxel model studies, paclitaxel was injected at several doses (2 mg/kg, i.p.; 4 mg/kg, i.p.; 2 mg/kg, i.v.) on alternate days (Day 0, 2, 4, 6) to determine the optimal dose and route of administration. For the oxaliplatin model studies, oxaliplatin (3 mg/kg, i.v.) was injected 2 days per week for a period of 4 weeks. Hind paw tactile sensitivity was determined with von Frey filaments using the up-down testing method as described by Chaplan et al., 1994, and hind paw cold sensitivity was determined using the acetone test. Effects of chemotherapeutic agents on hind paw sensitivity were evaluated for a maximum period of 8 weeks, and effects of mechanical and cold priming of the hind paws on the development of hypersensitivity were also examined.

Statistical analysis, effect size, and power analysis: Data were analyzed using two-way repeated measures ANOVA with Bonferroni’s or Dunnett’s post hoc test when appropriate. Effects of p < 0.05 were considered to be statistically significant. Power analysis and effect size were determined using SAS/STAT, and appropriate sample size was based on a power value of 0.8 to ensure adequate power for F-tests for two-way interactions.

Results: In the paclitaxel model studies, 4 injections of paclitaxel on alternate days (Day 0, 2, 4, 6) produced bilateral hind paw tactile and cold hypersensitivity which was maximal by Week 5 and persisted through Week 6. The paclitaxel dose of 4 mg/kg, i.p. was found to be optimal for this model, and results from rat pharmacokinetic studies demonstrated that Cmax and AUC values associated with this dose were similar to the values associated with efficacy in the clinic. Interestingly, hind paw priming with acetone during Week 2 enhanced acetone cold hypersensitivity in this model during Weeks 3-6, while mechanical priming with von Frey filament stimulation did not affect the development of tactile hypersensitivity. In the oxaliplatin model studies, oxaliplatin injection (3 mg/kg, i.v.) 2 days per week for a period of 4 weeks produced bilateral hind paw tactile and cold hypersensitivity which was maximal by Week 6 and persisted through Week 8. The magnitude of tactile and cold hypersensitivity was similar in the paclitaxel and oxaliplatin models.

Initial pharmacological characterization was performed in these models by examining the effects of morphine sulfate (0.3-3 mg/kg, s.c.) on bilateral hind paw hypersensitivity. Morphine sulfate (3 mg/kg, s.c.) was found to significantly inhibit bilateral tactile or cold hypersensitivity in the paclitaxel and oxaliplatin models at Week 6 and Week 7, respectively. Thus, these studies demonstrate that optimizing the dose of paclitaxel (4 mg/kg, i.p.) to be consistent with plasma exposure at clinically effective doses, enabled optimization of parameters in the model.

Importantly, both the paclitaxel and the oxaliplatin models showed (1) reproducible bilateral hind paw tactile and cold hypersensitivity in male and female rats in the paclitaxel and oxaliplatin models of chemotherapy-induced peripheral neuropathy, (2) bilateral hind paw hypersensitivity was enhanced through the use of hind paw priming procedures, and (3) hypersensitivity to both cold and tactile stimuli was significantly inhibited by morphine sulfate, demonstrating the effectiveness of an opioid in these models.

Conclusions: The validation of the paclitaxel and oxaliplatin models of chemotherapy-induced peripheral neuropathy further highlights efforts within the NIH HEAL Initiative’s PSPP program to validate endpoints and models to be incorporated into evaluating novel assets towards accelerating the development of novel non-opioid, non-addictive therapeutics.

Keywords: Pain Therapeutics, Preclinical Screening Platform for Pain, Chemotherapy-Induced Peripheral Neuropathy, Neuropathic Pain

Disclosure: PsychoGenics, Inc.: Employee, (Self)

P421. Automated Detection of Eye Tics Using a Computer Vision Approach

Christine Conelea*, Petros Apostolou, Megan DuBois, Mia Kellman, Brittany Raab, Alison Pryor, Suma Jacob, Nikos Papanikolopoulos, Kelvin Lim

University of Minnesota, Minneapolis, Minnesota, United States

Background: Tourette Syndrome (TS) a chronic, childhood-onset neurodevelopmental disorder that affects 1-3% of people. TS is characterized by tics: involuntary, repetitive movements and vocalizations. The most common and bothersome motor tics in treatment-seeking adults and children are visible movements of the face and upper body. Effective diagnosis and treatment depends upon accurate detection of tic presence and severity, yet there is a lack of objective, quantitative tools to measure tics. Video-based observational methods of measuring tics in research contexts have yielded critical insights into the symptomatology of TS. These methods produce accurate quantification of tics but are not readily scalable to the clinic due to reliance on trained human raters. Advances in computer vision and machine learning have enabled researchers to develop fully automated algorithms to detect clinically relevant abnormal movement in disorders such as autism and Parkinson’s disease. The aim of the current study was to develop and preliminarily test a computer vision approach to automate detection of eye tics.

Methods: A dataset of N = 39 videos of individuals with eye tics (eye blinking, eye darting/rolling, and/or eyebrow movements) was acquired from public YouTube postings using search terms of “Tourette” and “tic.” Videos were screened for relevance and quality during consensus team meetings and coded by human raters who met a training target of >80% reliability. A fine-grained tic coding scheme captured distinct aspects of observable tics (e.g., tic complexity, anatomical location). Codes were captured using DataVyu, a computer-assisted behavioral coding software program. A supervised machine learning approach was used to train a binary classifier to detect eye tics. Classifier development included four phases: data preprocessing, preparation of a convolutional neural network (CNN) based on DenseNet architecture, training the CNN to detect eye tics on a “training" set of coded videos, and applying the classifier to a “test” dataset (i.e., videos never before seen by the computer).

Results: The coded dataset included 198 images extracted from the N = 39 videos. The classifier demonstrated accuracy (agreement with human coder) of 84% with a Sensitivity of 75% and Specificity of 88%.

Conclusions: The binary classifier showed accuracy well within the accepted threshold of 80% for a human rater to be considered reliable. This preliminary study suggests that computer vision methods hold promise for automating detection of motor tics, an approach that could eventually improve screening, diagnosis, and treatment monitoring. Limitations are the focus only on eye tics and absence of clinical information for individuals in the videos. Use of single images as input data instead of multiple images from the video stream limited our ability to capture temporal information of the motor event. Future research using larger datasets that include videos of tic expression alongside clinical phenotyping and novel computer vision analytic techniques will further our ability to create scalable, quantitative clinical tools.

Keywords: Tourette Syndrome, Tic Disorders, Machine Learning Classification, Computer Vision

Disclosure: Posit Science: Grant (Self)

P422. Neuroimaging Probe Development for Receptor-Interacting Serine/Threonine-Protein Kinase 1

Changning Wang*

Harvard Medical School, Massachusetts General Hospital, Charlestown, Massachusetts, United States

Background: Necroptosis is a complex and regulated caspase-independent cell death mechanism mediated by various protein members, e.g. Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) involving inflammation. Notably, RIPK1 is dysregulated by microglial cells in human brains and mediates a disease-associated microglial response (DAM), which is related to an inflammatory response. Interestingly, down-regulation of RIPK1, by both pharmacological and genetic means, reduced disease pathology, corrected altered inflammatory changes in transgenic mouse models and in cell models. Thus, RIPK1 is an important therapeutic target for both understanding and treatment of human diseases. Here, our overarching goal is to develop the first positron emission tomography (PET) radiotracer of RIPK1/necroptosis. PET has provided a useful and indispensable way to both assist the patient selection for trials in medicine and improve pharmacological performance in drug development. However, there are no PET tracers that can image RIPK1 and necroptosis in the human brain and the mechanisms for in vivo selectivity, distribution and involvement of necroptosis in the neuro-pathophysiology remain elusive.

Despite the preclinical success and early clinical trial of RIPK1 inhibitors, a large knowledge gap exists between animal models and human diseases. In our opinion, this knowledge gap can in large part be filled by translational neuroimaging with the availability of a RIPK1 imaging biomarker. In order to fully support the therapeutic development for neurological disease, characterization of RIPK1 density and its dysregulation in the living human brain is required. In addition, understanding the relationship between RIP1 drug engagement in the brain and inhibitor dosing is essential to advancing the RIPK1 therapeutic discovery and dose selection process.

Methods: For PET imaging study, mice (both male/female) are utilized, anesthetized with inhalational isoflurane (Forane) at 3% in a carrier of 1.5-2 L/min medical oxygen and maintained with isoflurane for the duration of the scan. The mice are arranged in a Triumph Trimodality PET/CT/SPECT scanner and injected with radiolabeled compounds with/without pre-treatment of unlabeled RIPK1 inhibitors via a lateral tail vein catheterization at the start of PET acquisition. Dynamic PET acquisition is last for 60 min and followed by CT for anatomic co-registration. PET data are reconstructed using a 3D-MLEM method. Reconstructed images are exported from the scanner in DICOM format along with an anatomic CT for rodent studies. These files are imported to PMOD 4.01 (PMOD Technologies, Ltd.) and manually co-registered using six degrees of freedom. Volumes of interest (VOIs) are drawn manually as spheres in brain regions guided by high resolution CT structural images and summed PET data, with a radius no less than 1mm to minimize partial volume effects. Time-activity curves (TACs) are exported in terms of decay corrected activity per unit volume at specified time points with gradually increasing intervals.

Results: In past years, we have designed, radiosynthesized and evaluated several RIPK1 inhibitors as potential PET imaging probes, and some candidates displayed good brain uptake (%ID/cc > 1 for mice brain imaging), strong RIPK1 binding affinity (KD < 10 nM), good specificity and selectivity (no significant binding towards over 400 kinases), and appropriate kinetics and distribution profiles, strongly supporting the application as PET tracers in humans. We also further characterized the age and gender effects of RIPK1/ necroptosis in mice to support potential human imaging.

Conclusions: In summary, we fully expect that our RIPK1 probes will be useful for human neuroimaging study and are also able to serve as a putative biomarker that can significantly improve understanding of the pathogenesis of human diseases and rapidly enhance the drug development. The further characterization of these probes is undergoing and the best candidate will be moved forward for human imaging study.

Keywords: In Vivo Imaging, PET Probe, Neuroinflammation

Disclosure: Nothing to disclose.

P423. Characterizing Disease-Associated Missense Mutations in the GABA Transporter, GAT1

Benjamin Throesch*, Michelle Wennerholm, Pascal Bonaventure, Grace Woodruff

Janssen Research and Development, San Diego, California, United States

Background: Dysregulation of neural circuit excitatory/inhibitory balance may underlie multiple neuropsychiatric disorders. Genes involved in GABAergic neurotransmission, the main regulator of inhibition in the central nervous system, have been increasingly implicated in disease. SLC6A1 encodes the GABA transporter GAT1, one of two GABA transporters expressed in the brain. GAT1 primarily localizes to presynaptic terminals of GABAergic neurons, where it regulates GABAergic signaling through the re-uptake of GABA from the synaptic cleft. Knockout mouse studies have demonstrated impairment of GAT1 leads to abnormal GABA receptor signaling, alterations to hippocampal oscillations, abnormal social behavior, impairments in learning and memory, as well as deficits in prepulse inhibition. To date, over 85 unique mutations in the coding sequence of GAT1 have been identified in patients and associated with a wide variety of disorders including epilepsy, neurodevelopmental delay (NDD), autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), schizophrenia (SCZ), and Tourette Syndrome (TS). Previous studies have investigated a select cohort of variants primarily associated with epilepsy, ASD, and/or NDD and found them to all be loss-of-functions mutations. Here, we set out to characterize an extensive list of missense mutations across the complete spectrum of disorders associated with GAT1.

Methods: We introduced 42 missense mutations associated with a variety of disorders into the wild-type human GAT1 coding sequence and transiently overexpressed these variants in HEK293T cells. After 48 hours, cells were fixed, stained, and imaged on an Opera Phenix High-Content Screening System to quantify total GAT1 intensity and transfection efficiency. In parallel, transfected HEK293T cells were exposed to radiolabeled 3H-GABA to functionally measure GABA uptake. Radiouptake measurements were then normalized by transfection efficiency for each variant (n = 9, 3 independent transfections, 3 replicates per transfection). Data were analyzed using a one-way ANOVA with a Dunnett correction for multiple comparisons and graphed as the mean +/- SEM. The significance level was set at p < 0.05.

Results: Mean GAT1 intensity was decreased from wild-type only for the single mutation associated with TS, T46M (69.3 +/- 3.9%). No other variants showed a significant difference in GAT1 intensity. Radiouptake analysis demonstrated that 41/42 (97.6%) mutations significantly impacted GABA uptake. Most variants (39/42, 92.9%) were characterized as loss-of-function, with radiouptake scores ranging from 65.9% to 2.2% of wild-type. In addition, two mutations (4.8%) were gain-of-function with scores of 125.8% and 293.7% of wild-type.

To gain insight on how GAT1 function correlates with clinical phenotypes, we compared the level of GABA uptake for all mutations associated with a variety of disorders. Mutations associated with epilepsy, NDD, ASD, and ADHD showed on average severe loss-of-function (13.1%, 14.8%, 21.7%, and 15.1% respectively), whereas those associated with SCZ were only mildly impacted (71.5%). The unique mutation associated with TS showed a robust increase in function (293.7%).

Conclusions: Using a radiouptake assay, we functionally assessed 42 missense mutations in the GABA transporter, GAT1. Consistent with previous studies, most of the mutations were loss-of-function, yet two variants demonstrated enhanced GABA uptake. To our knowledge, this is the first observation of GAT1 gain-of-function mutations indicating bi-directional modulation of GABA uptake is relevant for neuropsychiatric disease. Furthermore, by correlating the uptake scores with clinical phenotypes, we were able to stratify disorders based on functional severity. Future experiments will investigate mechanisms underlying the changes to GAT1 function, including membrane localization and endoplasmic reticulum retention, and assess these mutants in GABAergic neurons derived from human induced pluripotent stem cells.

Keywords: GABA, SLC6A1/GAT1, Epilepsy, Schizophrenia (SCZ), Tourette Syndrome

Disclosure: Janssen Research and Development LLC. Employee (Self)

P424. Neuroprotective Effects of Cannabidiol in Human Neural Cell Lines Infected With SARS-CoV-2

Rafael Rinaldi Ferreira, Karla C.M. Costa, Isabela Pires-dos-Santos, Davi S. Scomparin, Franciele F. Scarante, Ronaldo Martins-Junior, Sabrina Batah, Alexandre T. Fabro, Isabella Guedes, Laurent Dardenne, Francisco S. Guimaraes, Jaime E.C. Hallak, Antonio W. Zuardi, Jose A. Crippa, Eurico Arruda-Neto, Alline Campos*

Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil

Background: COVID-19 has shown to be more than respiratory disease. Several good studies have demonstrated that the SARS-CoV-2 can cause long-term neurological symptoms such as headache, dizziness, stroke, cognitive and neuropsychiatric symptoms. Cannabidiol is the main non-psychotomimetic compound of Cannabis sp., with putative neuroprotective properties in different contexts of neurological disorders associated with infectious diseases (severe malaria, encephalomyelitis, meningitis). In rodent models, CBD prevented the long-term neurological and psychiatric effects of severe cerebral malaria. In the present study, we evaluate if Cannabidiol can prevent the deleterious effects of SARS-CoV-2 neuroinfection in an in vitro model.

Methods: In a first experiment, we evaluated in postmortem brain samples of COVID-19 patients (obtained by a minimally invasive technique) the presence and pattern of neuroinfection produced by SARS-CoV-2 (neurons and glial cells) and the presence of inflammatory markers (cytokines and chemokines). In a second experiment, the human glioblastoma cell line SH-SY5Y was incubated for 2h with SARS-CoV-2. After this period, cells were incubated with different concentrations of Cannabidiol, at concentrations of 100, 300, 1000, 3000, and 10000 nM at different time points (0h, 2h, or 4h). After the end of the experiments, we performed: a) MTT viability assay, b) BrdU proliferation assay, and qPCR for the detection/determination of SARS-CoV2 replication and cytokine production (cells and supernatant). In a final experiment, we conducted an in silico molecular docking to test the putative interaction of CBD with proteins and the primary cells targets of SARS-CoV-2.

Results:. The analysis of brain samples demonstrated that SARS-CoV-2 infects neurons and astrocytes, increasing the production of cytokines and chemokines in the tissue. In the in vitro experiments, CBD (at the doses of 1000nM and 3000nM) increased the viability and proliferation rate of SH-SY5Y infected with SARS-CoV-2. CBD (at the concentration of 1000 and 3000nM) increased the neuronal-like dendritic morphology of SH-SY5Y. In the qPCR assay, CBD increased the production of IL-10 mRNA. CBD did not decrease SARS-CoV-2 infection at any tested concentration. This latter effect was confirmed by the molecular docking results showing that CBD does not interact with the Spike and the N proteins of the virus or with the type 2 angiotensin-converting enzyme and the serine protease TMPRSS2.

Conclusions: Our results suggest a possible neuroprotective effect of Cannabidiol in the context of the neurological disorder burn associated with COVID-19. Our results are still preliminary, and more experiments are needed to confirm and better elucidate the mechanism behind CBD’s neuroprotective effects in models of SARS-CoV-2 neuroinfection.

Keywords: Cannabidiol, Novel Coronavirus (SARS-CoV-2), Neuroprotection

Disclosure: Nothing to disclose.

P425. Greater Monoamine Oxidase B Distribution Volume in the Cortex in Traumatic Brain Injury With Persistent Symptoms: An [11C]SL25.1188 Positron Emission Tomography Study

Jeffrey Meyer*, Yuko Koshimori, Michael Cusimano, Neil Vasdev, Ishrat Husain, Sho Moriguchi, Cynthia Xu, Emma Thomson, Isabelle Boileau, Kish Stephen

Centre for Addiction and Mental Health, Toronto, Canada

Background: Traumatic brain injury (TBI) has a lifetime prevalence of more than 10%, and a third of cases have long term symptoms, making TBI the most important cause of disability from neurological disease. There are no established pharmacological treatments for long term symptoms and a key barrier is a lack of targetable processes in community-based samples of human TBI, which are of mild to moderate severity representing about 90% of TBI cases.

Gliosis (proliferation and activation of glial cells) occurs in chronic traumatic encephalopathy, but it is unknown whether gliosis occurs in the more common TBI of mild to moderate severity. Astroglial activation (activation and proliferation of astrocytes) is correlated with monoamine oxidase B (MAO-B) level in neuropsychiatric disease and may be applied as a marker of gliosis. [11C]SL25.1188 positron emission tomography (PET) may be applied to measure MAO-B total distribution volume (MAO-B VT), an index of MAO-B density.

It is hypothesized that MAO-B VT is elevated in the prefrontal cortex as well as in other cortex, regions. Cortex regions are close to the skull and receive high levels of deformation stress in TBI models of direct and contra-coup injury, and the prefrontal cortex additionally plays an important role in cognitive functions often persistently affected by TBI.

Methods: Seventeen healthy and 23 TBI cases with persistent symptoms were recruited from the community in Toronto, Canada. [11C]SL25.1188 PET was applied to measure MAO-B VT, prioritizing the prefrontal cortex then other cortical regions, although a number of cortical and subcortical grey matter regions were also assessed. TBI cases had persistent symptoms since their last injury and no history of cigarette smoking, substance abuse, or psychotic illness.

Results: Patients with TBI had significantly greater MAO-B VT in the PFC (19%, F1,38 = 10.76, P = 0.002) and throughout the cortical regions (15%, F1,38 = 9.31; P = 0.004). The effect sizes (Cohen’s d) were robust in the cortical regions, ranging from 0.97 to 1.24.

Conclusions: MAO-B VT was considerably elevated in the TBI group with an effect size of ~1.1 across cortical regions. This is strongly supportive of astrogliosis in TBI with persistent symptoms from community-based samples. The effect size is particularly notable, being the largest among brain markers comparing mild to moderate severity TBI to controls. [11C]SL25.1188 PET shows intriguing promise for stratifying TBI cases with gliosis and monitoring treatments of TBI to reduce gliosis.

Keywords: Astrogliosis, Positron Emission Tomography (PET), Traumatic Brain Injury, Monoamine Oxidase B, Gliosis

Disclosure: Exceltis: Other Financial Or Material Support (Self)

Sanofi: Grant (Self),

CAMH: Patent (Self)

P426. The Effect of 5-HT1A Agonists on Psychiatric Symptoms in a Mouse Model of Parkinson’s Disease by Suppressing Activity of the Median Raphe Nucleus

Yukiko Ochiai*, Masayo Fujita, Yoko Hagino, Kazuto Kobayashi, Ryoichi Okiyama, Kazushi Takahashi, Kazutaka Ikeda

Tokyo Metropolitan Neurological Hospital, Tokyo, Japan

Background: Parkinson’s disease (PD) is a neurodegenerative disorder in which the degeneration of dopaminergic nerves in the substantia nigra is central to the pathogenesis of the disease. Psychosis in PD (PPD) such as hallucinations and delusions occurs in the advanced stages. The psychosis is now considered to be related to internal factors such as disease progression, external factors such as medications, and facilitating factors such as environmental changes and stress. Treatment is usually started with environmental adjustments and reduction of PD medications. Some of the drugs that have been reported to be effective for PD psychosis include clozapine, quetiapine, cholinesterase inhibitors and pimavanserin.

Dopamine-deficient (DD) mice are tyrosine hydroxylase knockout and do not produce dopamine, so they are maintained on L-dopa. DD mice move well after L-dopa administration, but show bradykinesia when dopamine in the brain is decreased. Surprisingly, they become hyperactive in a novel environment when DA level in the brain is below its detection. The hyperactivity of DD mice was suppressed by clozapine and donepezil.

In general, hyperactivity in mice is said to reflect psychiatric symptoms. We hypothesized that hyperlocomotion in DD mice would be a model mouse for PPD, since abnormal behavior (psychiatric symptoms) occurs under dopamine deficiency and is ameliorated by the common drugs clozapine and donepezil.

To investigate the relationship between serotonin and psychosis with PD, which remain largely unexplored, serotonin-based drugs were administered to DD mice exhibiting abnormal hyperlocomotion. For the effective drugs, immunohistochemical staining of brain samples using c-Fos was performed to investigate the cause.

Methods: DD mice are maintained with administration of L-dopa. Seventy-two hours after interruption of L-dopa administration, when DA level in the brain was below its detection, open field test (OFT) was performed; the mice were placed in a novel environment (35 × 40 × 25 cm) and locomotor activity was counted. Saline, quetiapine (multi-acting receptor-targeted antipsychotics; 20 mg/kg), pimavanserin (5-HT2A/2C inverse agonist; 5 mg/kg), tandspirone (5-HT1A agonist; 3 mg/kg) and paroxetine (selective serotonin reuptake inhibitor; 8 mg/kg) were injected into DD mice (n = 29, 20, 11, 10, 10, respectively) and wild type mice (n = 16, 21, 11, 12, 10, respectively) three hours after exposure to the novel environment. For each mouse, locomotion was monitored for additional three hours.

The drug was administered three hours after the start of OFT, and brain samples were collected from DD and wild-type mice one hour after that. We also collected brain samples from mice not exposed to the novel environment and brain samples taken four hours after the start of OFT without drug administration. c-Fos immunohistochemistry was performed to observe neuronal activity in the raphe nuclei. In the median raphe nucleus, c-Fos positive cells were counted in an area of 400 μm long x 100 μm wide, and in the rostral linear nucleus, cFos-positive cells were counted in an area of 200 μm long x 200 μm wide.

Results: DD mice gradually showed hyperactivity that could be regarded as a psychiatric symptom. Among the drugs administered, only quetiapine suppressed hyperactivity in DD mice. Administration of WAY100635 (5-HT receptor antagonist) 30 minutes before quetiapine partially cancelled the effect, suggesting quetiapine function may be mediated by serotonin receptors. To find out which subtype of receptor is involved, 8-OH-DPAT (5-HT1A agonist) and EMD281014 (5-HT2A antagonist) were administered, and 8-OH-DPAT was more effective.

Immunohistochemical staining was performed under quetiapine or 8-OH-DPAT treatment. During hyperactivity in DD mice, there was an increase in c-Fos-positive cells in the median raphe nucleus, which was reduced by quetiapine and more reduced by 8-OH-DPAT. In contrast, few c-Fos-positive cells were found in the rostral linear nucleus.

Conclusions: These results suggest that 5-HT1A receptors may be involved in PPD, and that drugs targeting 5-HT1A receptors may be useful in treating psychiatric symptoms. It is also possible that the median raphe nucleus, but not the rostral liner nucleus, is involved in the suppression effect of the drugs on hyperactivity.

Keywords: Parkinson’s Disease, Parkinson’s Disease and Dementia Psychosis, Mouse Models, Raphe Nucleus

Disclosure: Nothing to disclose.

P427. Vesicular Glutamate Transporter 2 Expression Mediates Sex Differences in Dopamine Neuron Resilience by Modifying Mitochondrial Oxidative Stress

Silas Buck, Tenzin Kunkhyen, Sophie Rubin, Claire Cheetham, Zachary Freyberg*

University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Background: Neurodegenerative illnesses including Parkinson’s disease (PD) is characterized by dopamine (DA) neuron loss, but some DA neurons are relatively protected compared to others. Clues for better understanding mechanisms of DA neuron resilience come from a distinct subpopulation of midbrain DA neurons that co-transmit glutamate. Multiple observations have shown: 1) midbrain DA neurons in the medial VTA are spared in brains of PD patients and in both primate and rodent models of PD; and 2) these resilient DA neurons express the vesicular glutamate transporter 2 (VGLUT2). Indeed, we and colleagues discovered that VGLUT2-expressing DA neurons are more likely to survive neurotoxic insults compared to DA neurons that do not express dVGLUT2. We previously demonstrated that DA neuron VGLUT2 enables DAergic synaptic vesicles to dynamically tune their vesicle content and enhance vesicular DA loading and release (Aguilar et al., 2017). These data therefore suggest that DA neuron VGLUT2 may be employed by surviving neurons to maintain adequate synaptic DA neurotransmission to compensate for ongoing DA neurodegeneration. However, to date, the mechanisms behind this protection conferred by VGLUT2 is still unknown. Considering the important role of mitochondrial dysfunction in DA neuron loss and PD etiology, we hypothesized that VGLUT2 expression may improve mitochondrial resilience to oxidative stress observed in DA neurons in animal models of PD and human PD. To test this hypothesis, we employed the genetically tractable Drosophila melanogaster model which expresses a single ortholog of VGLUT, Drosophila VGLUT (dVGLUT).

Methods: Drosophila strains: All Drosophila strains were maintained at 24C, ~50% humidity under a 12:12 hour light/dark cycle in humidity- and temperature-controlled incubators. We used the TH-GAL4 strain (gift of Dr. S. Birman, Université Aix-Marseille II-III, Marseille, France) (Friggi-Grelin et al., 2003) to drive expression in DA neurons via the GAL4/UAS binary expression system.

Brain imaging: To measure reactive oxygen species (ROS) in DA neurons, we imaged whole intact adult central brains expressing the MitoTimer ROS biosensor (Laker et al., 2014) via multiphoton microscopy.

dVGLUT knockdown: To ascertain effects of dVGLUT RNA interference (RNAi) KD on ROS in DA neurons, we used TH-GAL4-driven UAS-VGLUT-RNAi (UAS-Vglut-RNAi) co-expressed with MitoTimer. All fly strains were outcrossed for 10 generations into the w1118 wild-type genetic background. For all experiments utilizing drug treatments, flies were randomly assigned to vehicle or drug treatment groups.

RNAscope: Conduced in adult fly central brain as described earlier (Buck et al., 2021).

Results: We first validated DA neuron-specific RNAi KD of dVGLUT which caused a 36.1%-51.4% decrease in average number of dVGLUT mRNA grains in TH + neurons compared to control genotypes. Importantly, DA neuron knockdown of dVGLUT resulted in a 44.0%-63.6% decrease in TH + /dVGLUT+ neuron density, and a 51.3%-69.0% decrease in percent of TH + neurons that are dVGLUT + , reinforcing dVGLUT’s role as a neuroprotective factor in DA neurons. To test if dVGLUT’s neuroprotective properties are linked to its ability to lower neurotoxic ROS in DA neurons, we analyzed the impact of DA neuron dVGLUT knockdown on mitochondrial oxidative stress using flies that express MitoTimer, a mitochondria-targeted ROS biosensor in DA neurons. Notably, we discovered sex differences in mitochondrial ROS levels in vivo in DA neurons, finding that males possess ~40% more mitochondrial ROS compared to females (n = 5-8/group, p < 0.05). This suggests females’ lower ROS levels may contribute to their greater DA neuron resilience. We then tested our hypothesis that DA neuron dVGLUT lowers mitochondrial ROS to potentially contribute to these sex differences by knocking down dVGLUT in DA neurons via RNAi. dVGLUT KD indeed raised mitochondrial ROS. This was significantly pronounced in females compared to males (p < 0.01). Last, we examined effects of DA neuron dVGLUT KD in response to paraquat, a neurotoxicant that raises DA neuron ROS. dVGLUT RNAi KD exacerbated mitochondrial ROS in DA neurons in a region-specific manner (p < 0.05) with the greatest increase observed in the male dVGLUT RNAi group (P < 0.05).

Conclusions: Our findings uncover a novel mechanism of dVGLUT-mediated DA neuroprotection, highlighting VGLUT’s role in mediating sex differences in mitochondrial oxidative stress in DA neurons. These data suggest that an important source of increased DA neuron resilience in females is the capacity of these cells to diminish levels of toxic mitochondrial ROS via heightened dVGLUT expression versus males. This sex difference is relevant since PD in women is less prevalent and has a later age of symptomatic onset. Ultimately, determining the mechanisms of increased DA neuron resilience in females can be transferred to males to boost DA neuron survival in neurodegenerative diseases including PD. This may lead to new, effective treatments to either slow or stop DA neurodegeneration in both men and women.

Keywords: Dopamine, Glutamate, VGluT2 Neurons, Neurodegeneration

Disclosure: Nothing to disclose.

P428. Distinct Neuropsychiatric Features Define Three Subgroups of Female FMR1 Premutation Carriers

Lauren Schmitt*, Kelli Dominick, Ernest Pedapati, Rui Liu, Elizabeth Smith, John Sweeney, Craig Erickson

Cincinnati Children’s Hospital, Cincinnati, Ohio, United States

Background: Cytosine-guanine-guanine (CGG) trinucleotide repeats in the 5’ untranslated region of Fragile X mental retardation 1 (FMR1) gene over 200 results in a “full mutation” of Fragile X Syndrome (FXS), whereas 55-200 repeats results in a “premutation”. FMR1 premutation carriers (PMC) are characterized by a range of psychiatric, neurocognitive, and physical conditions, though different than those features associated with full mutation FXS. For example, previous studies have documented both intact and impaired executive function, social processing, and psychiatric features in female PMCs relative to age- and sex-matched typically-developing controls (TDC). CGG repeat length, Fragile X mental retardation protein (FMRP) levels, and degree of toxicity resulting from CGG repeat containing FMR1 mRNA, and environmental factors are thought to play a role in the variable neuropsychiatric feature presentation of PMC. Studies have reported both linear and non-linear relationships with CGG repeat length and neuropsychiatric symptoms. A bottom-up, data-driven approach to identify naturally occurring clusters of neuropsychiatric features in female PMCs may be an important step in parsing this heterogeneity, ultimately offering better insight into understanding underlying pathology and developing better screening, diagnostic, and treatment planning for this unique population.

Methods: Forty-one females (17-78 years) with 50-200 CGG repeats, or premutation carriers (PMC), and fifteen age- and-sex matched controls completed the study. PMC status (50-200 CGG repeats) was confirmed via genetic analysis or medical record review. All participants completed: 1) neurocognitive testing via the Test of Attentional Performance for Children (KiTAP), 2) self-report measures including Beck Depression Inventory, Second Edition (BDI-II), Anxiety Sensitivity Index (ASI), and Adult Sensory Profile (SP); 3) eye tracking using Tobii T120 of Farzan faces and social preference scenes; and 4) five-minute resting state EEG using EGI NetAmp400. First, we examined the feasibility to use cluster analysis to identify potential subgroups of female PMCs using K-means cluster analysis, in order to classify non-overlapping clusters with the lowest within-cluster variance and the highest between-cluster variance. Second, we examined inter-correlations between neuropsychiatric features and CGG repeat count within each cluster membership. Last, we conducted separate univariate ANOVAs for each variable of interest for each task with the between subjects’ factor group (PMC vs TDC).

Results: Female PMC and TDC did not differ on IQ, depression or anxiety symptoms, or social or sensory processing. Across frequency ranges, groups also did not differ on relative power. Only subtle impairments in specific executive function domains, including processing speed and distractibility, were observed for female PMCs. We found a three cluster solution using k-means clustering. Cluster 1 represented a psychiatric feature group (27% of our sample); Cluster 2 represented a group with executive dysfunction and elevated high frequency neural oscillatory activity (32%); and Cluster 3 represented a relatively unaffected group (41%). In addition, female PMCs within Cluster 1 demonstrated significant relationship between psychiatric symptoms and higher CGG repeat count. Similarly, female PMCs in Cluster 2 with more aberrant theta and gamma power had higher CGG repeat counts, although this subgroup had the lowest percentage of females in the high CGG repeat category. Although Cluster 3 demonstrated increased theta power and reduced alpha power compared to TDC, this subgroup was observed to have relatively spared neuropsychiatric functions.

Conclusions: Consistent with prior reports, our overall sample of female PMCs has relatively preserved psychiatric, cognitive, social, and electrophysiological functioning. However, by using a bottom-up approach to subgroup clustering using a wide array of quantitative assessments, we were able to identify three distinct clinically-meaningful clusters with good clinical face-validity. We also showed that CGG repeat count and its association with neuropsychiatric features differed across clusters. Thus, our findings indicate the feasibility of using a data-driven approach to identify naturally occurring clusters in female PMCs using a multi-method assessment battery. Ultimately, our findings provide important insight into potential diverging pathophysiological mechanisms and risk factors for each female PMC cluster, which may help provide new insights into pathology associated with FMR1 gene and potential treatment options.

Keywords: FMR1 Premutation, Cluster Analysis, Neuropsychiatric Disorders, Psychiatric Genetics

Disclosure: Nothing to disclose.

P429. NIH HEAL Initiative: National Institute of Neurological Disorders and Stroke’s Early Phase Pain Investigation Clinical Network (EPPIC-Net)

Carlos Faraco*, Rebecca Hommer, Jennifer Beierlein, Marlene Peters-Lawrence, Clinton B. Wright, Barbara I. Karp

National Institute of Neurological Disorders and Stroke (NINDS), Rockville, Maryland, United States

Background: The NIH Helping to End Addiction Long-term SM (HEAL) Initiative focuses on efforts to advance scientific solutions to eradicate the opioid crisis by improving prevention and treatment of opioid misuse/addiction and enhancing pain management by accelerating early-phase clinical trials of non-addictive pain therapeutics (“assets”).

Methods: Within the HEAL Initiative, NINDS has been tasked with identifying, developing, and testing non-addictive pharmacologic and non-pharmacologic therapeutics (“assets”) targeted to pain conditions of high unmet need. NINDS established the Early Phase Pain Investigation Clinical Network (EPPIC-Net) to accelerate and enhance pain therapeutic development by carrying-out phase 2 clinical trials of non-addictive pain therapies. EPPIC-Net evaluates new, as well as repurposed, small molecules, biologics, drugs, natural products, and devices submitted by industry, academic, or other partners for studies across the age and pain condition spectrum. The ideal asset has adequate data to support a phase 2 clinical trial and has an existing IND/IDE or is IND/IDE-ready. EPPIC-Net infrastructure includes a Clinical Coordinating Center, a Data Coordinating Center, and 12 Specialized Clinical Sites with access to broad, inclusive patient populations to provide phase 2 clinical trials, incorporating proof-of-concept testing, biomarkers validation, novel study design, and protocol development and implementation.

Results: EPPIC-Net aims to provide a robust and readily accessible infrastructure with a network comprised of pain experts who will design, conduct, and provide data analysis for phase 2 trials built around submitted potential pain therapeutic assets at no cost to the asset provider. The applicant is expected to provide the asset and matched placebo for the study. The asset owner retains intellectual property rights to their asset. It is anticipated that successful phase 2 trials will enable the applicant to continue to phase III studies and further development of the asset outside of EPPIC-Net. Ultimately, EPPIC-Net will reduce reliance on opioids by accelerating development of non-addictive pain therapeutics.

Conclusions: This abstract describes the NIH HEAL Initiative EPPIC-Net program, charged with evaluating pain therapeutics in phase 2 clinical development. EPPIC-Net accepts applications on a rolling basis; EPPIC-Net seeks innovative non-addictive treatments for any pain condition that lacks adequate treatment, spanning the age spectrum from children to old age.

Keywords: Opioid Addiction, Phase II Clinical Trial, Non-Opioid, Non-Addictive Therapeutics

Disclosure: Nothing to disclose.

P430. Aberrant Anterior Cingulate Cortex Activity in HIV + Adults With High Early-Life Stress Exposure: Relation to Cognitive Efficiency

Uraina Clark*, Jordan Sergio, Dorothea Dwomoh, Rachal Hegde

Icahn School of Medicine at Mount Sinai, New York, New York, United States

Background: High early-life stress (ELS) exposure is associated with greater cognitive impairments in adults living with HIV, yet the neural correlates underlying these effects remain poorly understood. The anterior cingulate cortex (ACC) is one of few brain regions in which abnormalities in neural structure and function are observed in both HIV + adults and adults with high ELS. Although aberrant activity within the subgenual ACC (sgACC) is known to contribute to cognitive dysfunction, the combined effects of HIV and high ELS exposure on sgACC activity have received little investigation. Here, we examined the independent and combined effects of HIV and high ELS exposure on sgACC function and its relation to cognitive efficiency.

Methods: We included 49 HIV + adults (26 with high ELS) and 45 demographically-matched healthy control adults (24 with high ELS). fMRI was used to assess sgACC function during a verbal working memory task, the N-back. Our task included several N-back conditions (e.g., 1back, 2back, 3back) where larger Ns provide increased cognitive load. To capture neural response associated with increased cognitive load, we examined sgACC function during the 3back relative to the 1back. Participants with low N-back accuracy (A’ < .70), low N-back response rate (<80%), excessive movement during the N-back (>2mm), or positive hepatitis C status were excluded. We utilized a behavioral index of cognitive efficiency previously shown to be sensitive to cognitive impairment in HIV + samples, reaction time intra-individual variability (RT-IIV), to measure cognitive efficiency during the 3back, where higher RT-IIV scores indicate poorer efficiency. Using a region of interest (ROI) approach, we calculated the mean BOLD response within a 5-mm radius sphere centered on coordinates for the sgACC. The independent and combined effects of HIV and high ELS status on sgACC function were examined using ANCOVA, controlling for variables on which the groups differed significantly (e.g., current stress). Associations between sgACC and cognitive efficiency (RT-IIV) were examined using linear regression.

Results: Across the entire group, the 3back elicited expected patterns of verbal working memory activation (e.g., middle frontal gyrus) and deactivation (e.g., ACC, fully encompassing our sgACC ROI) (p < .05, FDR corrected) consistent with active suppression of the default mode network (DMN). Analyses of sgACC function revealed a significant interaction effect between HIV and ELS status (F = 5.67, p = .020, partial eta-squared = .09), as well as a significant main effect of ELS status (F = 7.57, p = .008, partial eta-squared = .11). Follow-up analyses indicated that these effects were driven by greater 3back-induced sgACC deactivation in the HIV + high ELS group relative to all other groups (p’s < .032). In the HIV + high ELS group, sgACC function correlated significantly with RT-IIV (beta = .510, p = .037), such that participants who exhibited greater 3back-induced deactivation also exhibited greater cognitive efficiency. This association was maintained (beta = .496, p = .046) even when controlling for 3back performance (accuracy).

Conclusions: These findings demonstrate for the first time ELS-related functional abnormality in the sgACC in HIV + adults. Further, our data align with studies linking cognitive difficulty to a failure to suppress DMN functions. Greater sgACC deactivation in HIV + high ELS adults may reflect an adaptive dynamic downregulation of DMN-related processes (e.g., internal state monitoring) during high cognitive-load tasks. The observed association between sgACC deactivation and cognitive efficiency thus implicates ELS-related DMN abnormalities in cognitive difficulties experienced by HIV + high ELS adults.

Keywords: HIV, Adverse Childhood Experiences (ACE), Early-Life Stress, Cognitive Symptoms, Subgenual Anterior Cingulate

Disclosure: Nothing to disclose.

P431. Aberrant Cortical Neurophysiology in a Patient-Derived NMDA Receptor GRIN1 Y647S +/- Mutant Mouse: Characterization and Pharmacological Interventions

Sridevi Venkatsan*, Amy Ramsey, Evelyn Lambe

University of Toronto, Toronto, Canada

Background: NMDA receptors (NMDARs) are essential for brain function and enable supralinear integration of glutamatergic inputs to generate dendritic plateau potentials. GRIN1 neurodevelopmental disorder is a rare condition caused by de novo mutations in the gene encoding the obligate GluN1 NMDAR subunit. This genetic disorder is characterized by profound neurological deficits and seizures. However, little is known about the neurophysiological deficits as the consequences of various human GRIN1 mutations on NMDAR function and dendritic integration are unknown. Therefore, we characterized the neurophysiological consequences of a patient-derived GRIN1 mutation (Y647S), using a heterozygous transgenic mouse model. These experimental results give new insight into dynamic interactions between NMDARs and proximal ion channels and identify a new research direction for GRIN disorder treatment.

Methods: Transgenic mutant mice (Grin1 Y647S +/-) and wildtype littermate mice of both sexes were used. Patch clamp electrophysiology of layer 5 pyramidal neurons in the prefrontal cortex examined three different aspects of NMDA receptor functionality: (1) whole-cell currents evoked by bath application of NMDA as a broad measure of NMDAR levels and activity; (2) electrically-evoked excitatory postsynaptic currents (EPSCs) for functional assessment of cortical synapses; and (3) dendritic plateau potentials for characterization of NMDAR mediated dendritic integration.

Results: We found unexpected complexities in the prefrontal cortical neurophysiology in mice heterozygous for the patient-variant Grin1 Y647S +/- mutation, with paradoxical gain- and loss-of-function of different aspects of cortical NMDAR signaling. Whole-cell currents evoked by bath applied NMDA were dramatically enhanced in the Grin1 Y647S +/- mice (t(17) = 3.88, p = 0.0012). By contrast, electrically-evoked pharmacologically-isolated NMDAR EPSCs show significant reduction in the Grin1 Y647S +/- mice (Interaction between stimulus intensity and genotype: F(7,112) = 3.809, p = 0.001). Ongoing examination of NMDAR-mediated dendritic plateau potentials shows reduced burst firing, but greatly prolonged depolarization in Grin1 Y647S +/- mice. The combined data suggests deficient NMDAR together with a dysregulation in their typical recruitment of calcium-activated potassium channels. Drugs that potentiate calcium-activated potassium channels, such as NS309, show promise in restoring appropriate timing of NMDAR-dependent integration.

Conclusions: We have characterized the consequences of the patient-derived Grin1 Y647S +/- mutation for multiple aspects of prefrontal neurophysiology. It results in a multi-faceted dysregulation arising via reduction of NMDARs themselves but also their recruitment of tightly linked ion channels. Ongoing work is refining a pharmacological strategy to restore appropriate NMDAR signaling in these mice

Keywords: GRIN-Related Disorders, NMDA Receptor, GRIN1 Mutation, Cortical Excitability, Ion Channels

Disclosure: Nothing to disclose.

P432. The NIH HEAL Initiative Preclinical Screening Platform for Pain (PSPP) Efforts to Accelerate Development of Non-Opioid, Non-Addictive Pain Therapeutics: Validation of the Monoiodoacetate Model of Osteoarthritis Pain in the Rat

Smriti Iyengar*, Sarah A. Woller, Katelyn Buban, Jennifer Hagedorn, Philip Wig, Taleen Hanania, Mark O. Urban

NINDS/NIH, Bethesda, Maryland, United States

Background: The National Institutes of Health Helping to End Addiction Long-termSM Initiative, or NIH HEAL InitiativeSM, Preclinical Screening Platform for Pain (PSPP) program aims to accelerate the discovery and development of new non-opioid, non-addictive pain therapeutics. Towards this goal, PSPP is collaborating with PsychoGenics, Inc. to validate preclinical models and endpoints to enable screening and profiling of assets, including small molecules, biologics, natural products, and devices. Here, we describe the validation of one such effort to optimize the monoiodoacetate (MIA) model of osteoarthritis pain in the rat. Intraarticular injection of MIA into the rat hindlimb knee joint results in cartilage degeneration, localized inflammation, and pain behaviors that are thought to resemble those seen in human osteoarthritis (OA).

Methods: Adult male and female Sprague Dawley rats (N = 10, each sex) were used in these studies. MIA (0.3 – 3 mg) was injected intraarticularly into the left hindlimb knee joint. Tactile sensitivity (von Frey testing using the up down method as described by Chaplan et al., 1994), weight bearing, changes in gait, and paw pressure were systematically evaluated in both sexes for 4-6 weeks. Following this systematic phenotyping, pharmacological validation of the model was established using morphine (3 mg/kg), duloxetine (60 mg/kg), and ketoprofen (6 mg/kg) after acute and repeated dosing.

Statistical analysis, effect size, and power analysis: Data were analyzed using two-way repeated measures ANOVA with Bonferroni’s or Dunnett’s post hoc test when appropriate. Effects at p < 0.05 were considered to be statistically significant. Power analysis and effect size were determined using SAS/STAT, and appropriate sample size was based on a power value of 0.8 to ensure adequate power for F-tests for two-way interactions.

Results: Intraarticular injection of MIA (1 and 3 mg) into the hindlimb knee joint produced unilateral hind paw tactile hypersensitivity which was maximal at week 2 post MIA injection in both male and female rats. Changes in gait were also observed in male and female rats following MIA injection at weeks 1 and 2 post MIA injection. Both static and dynamic weight bearing were evaluated in both sexes. Deficits were modest when measuring static weight bearing, but more pronounced when measuring dynamic weight bearing in both male and female rats at 1 week post MIA injection. While female rats showed hypersensitivity to pressure and pinch stimuli at week 2 post MIA injection, this effect was not observed in male rats.

We then evaluated the efficacy of several analgesics on dynamic weight bearing in rats injected with MIA (1 mg). Acute subcutaneous injection of morphine (3 mg/kg) reduced hind paw tactile hypersensitivity and weight bearing deficits in male and female rats, whereas acute oral administration of ketoprofen (6 mg/kg) and duloxetine (60 mg/kg) were less effective. In contrast, repeated treatment with ketoprofen or duloxetine (4 days, b.i.d.) significantly reduced tactile hypersensitivity and weight bearing deficits.

These studies further helped establish inclusion and exclusion criteria for using various endpoints in this model and will be described in detail in this presentation.

Conclusions: The results from these validation studies using evoked and non-evoked endpoints in the rat MIA model suggest that both tactile sensitivity and dynamic weight bearing in the acute and repeated treatment paradigms of the MIA model may be used to identify and differentiate novel therapeutics for treatment of osteoarthritis. This example highlights efforts within the NIH HEAL Initiative’s PSPP program to validate endpoints and models to be incorporated into evaluating novel assets towards accelerating the development of novel non-opioid, non-addictive therapeutics.

Keywords: NIH HEAL Initiative, Preclinical Screening Platform for Pain, Non-Opioid, Non-Addictive Therapeutics, Monoiodoacetate Model of Osteoarthritis

Disclosure: National Institutes of Health: Employee (Self)

Retiree, Eli Lilly and Company: Other Financial or Material Support (Self)

P433. Transdiagnostic Anxiety-Related Increases in Information Sampling Associated With Altered Valuation

Amy Rapp*, Brandon K. Ashinoff, Seth Baker, Helen Blair Simpson, Guillermo Horga

Columbia University,New York State Psychiatric Institute, New York, New York, United States

Background: The ability to gather an appropriate amount of information about one’s environment and use this information effectively is critical for adaptive decision-making. In certain psychiatric disorders characterized by high trait anxiety, excessive information seeking can drive maladaptive responses to the environment (e.g., compulsive checking in obsessive-compulsive disorder [OCD], eliciting reassurance in generalized anxiety disorder).

Increased information seeking in psychiatric patients has been linked with alterations in inferential and valuation processes, although findings have been inconsistent. In part this is attributable to the use of information sampling tasks that lack appropriate controls for decision-making processes or task design elements that could influence task performance (e.g., time-pressure to make a decision, lack of motivation). To more precisely clarify the mechanisms associated with increased information seeking in individuals with high trait anxiety, computational models of inference and valuation were applied to data collected from a transdiagnostic sample of adults using a version of the beads task that improved on previous designs by accounting for potential confounds.

Methods: Participants (55% female, 45% male; M(SD) age = 27.6(7.3)) included 18 individuals diagnosed with OCD, 17 individuals with an anxiety disorder, and 23 healthy controls. No participants were taking psychotropic medications for at least 4-8 weeks prior to study enrollment.

Participants were told that at the start of each trial, either a jar with mostly blue beads or mostly green beads was selected at random and concealed from them, and their goal was to correctly guess the identity of the jar. Each jar had one of four majority-to-minority ratios of green or blue beads (“bead-ratio” conditions: 60:40, 75:25, 90:10, or 100:0 [control condition]) that was told to the participant at the start of the trial. Participants were able to draw up to a maximum of eight beads from the hidden jar. Within each trial, participants provided an estimate of the hidden jar’s identity prior to drawing any beads (i.e., a baseline measure of “prior belief”), then given the choice of drawing a bead or guessing the jar’s identity. Probability estimates were provided again after the bead was displayed. Participants were incentivized to earn up to $30 cash, with a $0.30 penalty for requesting an additional bead and a $15 penalty for incorrectly guessing the identity of the hidden jar.

First, a model of belief updating was fit to reported draw-by-draw probability estimates. Informed by Bayes’ theorem, this model quantified the iterative process by which new information (i.e., bead color) and prior beliefs were integrated to influence current beliefs (i.e., jar identity). This model consisted of four key parameters, including ⍵1 (the prior weight), reflecting the degree to which evidence presented earlier in the trial contributed to the posterior belief, and three ⍵2 parameters, one for each bead-ratio condition (60:40, 75:25, 90:10), representing the contribution of new information on posterior beliefs.

Next, a parameterized partially-observed Markov decision process ideal-observer model was used to understand the contribution of value-based decision making to sampling behavior (i.e., draws-to-decision; DTD). This model was comprised of three subjective cost parameters, Csub, one for each bead-ratio condition, and γ, the inverse-temperature parameter reflecting choice stochasticity.

Results: A repeated-measures ANOVA revealed a difference in DTD across bead-ratio conditions by trait anxiety, F(2, 114) = 3.17, p = 0.04. Post-hoc analyses of this significant interaction showed that trait anxiety was correlated with mean DTD only in the 90:10 bead-ratio condition, r = 0.29, p = 0.03.

Of the key parameters from potential explanatory models (⍵1, ⍵2(0.9), Csub(0.9), γ), the only parameter that satisfactorily accounted for the association of trait anxiety and DTD behavior in the 90:10 bead-ratio condition was Csub(0.9). Specifically, lower Csub(0.9) was associated with more trait anxiety, r = -0.51, p < 0.0001, and more DTD in the 90:10 bead-ratio condition, r = -0.76, p < 0.0001, suggesting that individuals who perceived the cost of drawing a bead to be smaller (or the cost of an incorrect guess to be larger) were higher in trait anxiety and engaged in greater information seeking.

Of note, lower ⍵1 was associated with higher trait anxiety, r = -0.28, p = 0.03, suggesting that individuals with greater trait anxiety were more likely to demonstrate a recency bias, but ⍵1 was not associated with DTD in the 90:10 condition. Although ⍵1 and Csub(0.9) shared variance, r = 0.29, p = 0.03, in a linear regression model predicting trait anxiety from ⍵1 and Csub(0.9), only Csub(0.9) retained significance, p = 0.005.

Conclusions: Dimensional trait anxiety correlated with increased information sampling (more DTD) in a condition with high objective evidence strength (90:10 bead-ratio condition). This was not explained by differences in weighting of new or old information, but rather by a different cost-benefit analysis suggesting that individuals with greater trait anxiety placed a higher subjective cost to incorrect guesses in relatively unambiguous contexts. Findings align with prior research that has identified alterations in valuation processes among patients with OCD and anxiety disorders and provide insight into potential mechanisms of maladaptive clinical characteristics of these disorders.

Keywords: Computational Modeling, Transdiagnostic, Anxiety, Obsessive Compulsive Disorder

Disclosure: Nothing to disclose.

P434. How Do Obsessive-Compulsive Symptoms and Traits Impair Adjustment to the Easing of COVID-19 Restrictions?

Naomi Fineberg*, Luca Pellegrini, Samuel Chamberlain, Aaron Clarke, Julius Burkauskas, Keith Laws

University of Hertfordshire, UK, Welwyn Garden City, United Kingdom

Background: Adjusting to a changing lifestyle as COVID-19 restrictions ease will be important for public mental health, psychosocial wellbeing and economic recovery. Our previous study surveyed adult members of the public (n = 438) during a temporary release of lockdown (July to November 2020) and showed that those with a history of mental disorder and obsessive-compulsive (OC) personality traits and symptoms, alongside those showing cognitive rigidity on an objective task, found adjustment problematic (Fineberg et al., 2021; Journal of Psychiatric Research). In this secondary analysis of the original study data, we aim to clarify the specific OC traits and symptoms impacting most on three key COVID-related behaviors: problematic adjustment, avoidance and disinfecting, as a further step toward identifying those most at risk and how they are affected.

Methods: A series of correlational analyses, followed by multiple regression analyses, was performed to determine the associations between individual OC personality traits and symptoms, measured on the self-rated Compulsive Personality Assessment Scale (CPAS) and Obsessive-Compulsive Inventory Revised (OCI-R), respectively, and self-rated problematic adjustment, avoidance and disinfecting behaviors. Statistical analyses were conducted using IBM SPSS Statistics for Windows, version 27.0 (IBM Corp., Armonk, N.Y., USA). Bonferroni correction for multiple comparisons was applied.

Results: Difficulties adjusting in general correlated with perfectionism, preoccupation with details and rules, over-conscientiousness, need for control, contamination obsessions and compulsions, checking compulsions, difficulties controlling one’s thoughts and counting compulsions; social avoidance correlated with perfectionism, preoccupation with details and rules, contamination obsessions and compulsions, checking compulsions and difficulties controlling one’s thoughts; while disinfecting behaviors correlated with preoccupation with details and rules, miserliness, contamination obsessions and compulsions, checking compulsions and difficulties controlling one’s thoughts (Pearson’s r - all p < .001). Regression analysis of the scores on these specific items explained a greater amount of the variance than did analysis of the total CPAS or OCI-R. Intriguingly, self-rated rigidity did not relate to any of these problematic behaviors.

Conclusions: Several OC personality traits and specific symptoms from two of the four phenotypic OCD dimensions (contamination and/or cleaning, obsessions and/or checking) (Mataix-Cols et al., 2005; American Journal of Psychiatry) predict problems adjusting. This finding may be used by policy makers to identify those members of the public potentially most at risk as lockdown restrictions ease. The failure to detect an association between adjustment difficulties and a self-rated measure of cognitive rigidity (CPAS item 8) may reflect the impairment in metacognition and insight previously recognized as being integral to this personality trait (Oltmanns et al., 2005; Consciousness and Cognition), and suggests that rigidity may be better evaluated using an objective test. General adjustment difficulties were accompanied by problematic social avoidance and disinfecting behaviors, which could represent targets for public-health intervention.

Keywords: OCD Phenotypes, Obsessive-Compulsive Personality Traits, COVID-19, Prevention, Adjustment

Disclosure: Nothing to disclose.

P436. Abnormal Midfrontal Theta-Band Activity During Response Monitoring in Children With Obsessive-Compulsive Disorder

Takakuni Suzuki*, Pan Gu, Tyler Grove, Taeah Hammond, Kelsey Collins, Preetha Pamidighantam, Paul D. Arnold, Stephan Taylor, Yanni Liu, William Gehring, Gregory Hanna, Ivy Tso

University of Michigan Medical School, Ann Arbor, Michigan, United States

Background: The error-related negativity (ERN), one of the most investigated event-related potentials (ERPs), is the negative deflection in midfrontal electroencephalogram (EEG) recording after a commission of an error. Abnormal ERN activity occurs in various psychiatric conditions, most consistently observed as abnormally enhanced in individuals with obsessive-compulsive disorder (OCD), presumably linked to underlying neurophysiological mechanisms. ERPs reflect the summation of neural oscillatory activities that underlie brain region communications and could arise from increase in total power and/or increase in intertrial phase coherence (ITPC) of neural oscillatory activity. The ERN, in particular, is thought to reflect increased total power and partially by increased ITPC in theta-band (4-8 Hz) activity. Therefore, this study sought to investigate the theta-band power and ITPC abnormalities in OCD patients during response monitoring to enable a richer understanding into the underlying neurophysiology of this condition.

Methods: EEG was recorded from 99 pediatric patients with OCD and 99 healthy control (HC) participants while they completed the arrow flanker task. Participants were selected from a larger data, matching for sex (OCD 61% female; HC 55% female) and age (OCD M = 13.75; HC M = 13.68) across groups. Time-frequency analysis was conducted to extract theta-band power and ITPC from a midfrontal channel (Cz). Two mixed ANCOVAs, including sex and accuracy as covariates, were conducted to investigate the effects of group (OCD, HC) and response type (error, correct) on post-response theta-band (1) power and (2) ITPC. We hypothesized that there would be main effects of Group and Response Type, as well as an interaction effect. Specifically, we hypothesized that OCD patients will have larger theta-band power and ITPC than HC participants, error trials will have larger theta-band power and ITPC than correct trials, and OCD patients will have a larger difference in theta-band power and ITPC between error and correct trials than HC participants.

Results: Theta-band power was larger on error trials than on correct trials (F[1,198] = 416.659, p < .001), and larger in OCD patients than in HC participants (F[1, 198] = 4.720, p = .031). There was no Group x Response Type interaction (F[1,198] = 1.014, p = .315) on power. Theta-band ITPC was also larger on error trials than correct trials (F[1,198] = 17.832, p < .001). However, there was no main effect of group (F[1, 198] = 0.018, p = .894) and there was no Group x Response Type interaction (F[1,198] = 1.172, p = .280) on ITPC

Conclusions: Increase in both theta-band power and ITPC seems to underlie the ERN. OCD patients, however, only have enhanced theta-band power, regardless of response type, and did not differ from HC participants in ITPC. These data suggest that pediatric patients with OCD have general difficulty in regulating response monitoring or general compensatory mechanism. At the same time, this difficulty seems to be specific to neural mechanisms that would underlie increase in power, but not an increase in ITPC. The findings are expected to help identify novel brain-based treatment targeting neural oscillatory activity, such as transcranial alternating current stimulation.

Keywords: Obsessive Compulsive Disorder, EEG Electrophysiology, Time-Frequency, Error Processing

Disclosure: Nothing to disclose.

P437. Distinct Roles for Norepinephrine and Dopamine Receptor Signaling in the Control of Stress-Induced Repetitive Behaviors

Daniel Lustberg*, Joyce Liu, Katharine McCann, David Weinshenker

Emory University School of Medicine, Atlanta, Georgia, United States

Background: Tourette’s syndrome (TS) is a childhood onset neurological disorder that affects 1% of the population and is highly co-morbid with obsessive-compulsive disorder (OCD). TS is characterized by uncontrollable, repetitive behavioral tics that are preceded by aversive premonitory sensations and exacerbated by stress. Antipsychotic drugs which block dopamine (DA) receptors are the first line of treatment for reducing motor and vocal tics in TS, but the effectiveness of these medications is limited by a wide range of adverse side effects. Because these drugs are poorly tolerated, antipsychotic therapy is often discontinued in pediatric TS patients, which comprise the majority of cases. Although not FDA-approved for the treatment of TS, clonidine is widely used off-label for this disorder because it reduces tic severity and has milder side effects than antipsychotic drugs, although the mechanism by which clonidine attenuates TS symptoms remains unknown. Clonidine belongs to a class of drugs that suppress norepinephrine (NE) transmission by activating inhibitory α2 autoreceptors on NE neurons. The locus coeruleus (LC) is the primary source of NE in the central nervous system, projecting extensively within forebrain circuits that govern attention, arousal, stress responses, and motivated behavior. We have previously shown that NE is required for repetitive behaviors induced by cage-change stress, such as nestlet shredding and marble burying, using NE-deficient dopamine β-hydroxylase knockout (Dbh-/-) mice and their NE-competent littermate controls. In this study, we used predator odor to induce repetitive behaviors, arousal, and exploratory behavior, and examined abnormalities in these innate stress responses and neuronal activity related to NE deficiency and/or augmented DA release in Dbh-/- mice and their Dbh +/- littermate controls.

Methods: Dbh-/- and Dbh +/- control mice (n = 30 per genotype) of both sexes were exposed to a new clean cage with a nestlet treated with either bobcat urine or a novel neutral odorant (essential oil) for 90 min, and repetitive behaviors, arousal, exploratory behavior, and time spent in contact with the nestlet were measured. Immediately following the test, mice were euthanized, and brains were processed for c-fos immunohistochemistry in the LC and several target regions implicated in behavioral responses to innately stressful predator odorants.

Results: Dbh-/- mice showed high levels of grooming (p < 0.001) and low levels of digging (p < 0.05) relative to controls regardless of odorant. However, while control mice sustained high levels of arousal throughout the predator odor condition, Dbh-/- mice also fell asleep within 90 min (p < 0.001). The odor-induced high grooming/low digging phenotype of the Dbh-/- mice was recapitulated in controls pretreated with the DBH inhibitor nepicastat. Excessive grooming behavior in Dbh-/- mice elicited by novel odorants was blocked by systemic administration of the DA receptor antagonist flupenthixol. In control mice, systemic administration of a cocktail of NE receptor antagonists resulted in virtually complete suppression of all typical repetitive and exploratory behaviors, including digging, in response to novel odorants. Compared with controls exposed to predator odor, Dbh-/- mice demonstrated increased c-fos induction in the LC and the medial amygdala, but decreased c-fos in the anterior cingulate cortex, lateral septum, periaqueductal gray, and bed nucleus of the stria terminalis. Intriguingly, c-fos induction in the paraventricular nucleus of the hypothalamus was similarly high in mice of both genotypes.

Conclusions: These findings indicate that DA receptors control grooming, while NE receptors control exploratory behavior and digging elicited by odorant stress. Further, the results of our current study using odorant stress support our previous findings that anti-adrenergic drugs exhibit anti-compulsive effects in the marble burying and nestlet shredding models of TS/OCD. Because the neurobiological basis of TS remains poorly understood, there is a paucity of efficacious drugs for the treatment of this disorder. We propose that NE and DA may contribute separable roles in the expression of repetitive behaviors in TS and OCD, particularly following exposure to stress. Thus, anti-adrenergic drugs could be effective for the treatment of compulsive disorders.

Keywords: Tourette syndrome, OCD, Acute Stress, c-Fos, Norepinephrine

Disclosure: Nothing to disclose.

P438. Independent and Distinct Patterns of Abnormal Lateral Orbitofrontal Cortex Activity During Compulsive Grooming and Reversal Learning Normalize After Fluoxetine

Matt Geramita*, Elizabeth Manning, Sean Piantadosi, Susanne Ahmari

University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Background: Patients with obsessive-compulsive disorder (OCD) display disrupted performance and abnormal lateral orbitofrontal cortex (LOFC) activity during reversal learning tasks, yet it is unknown whether compulsions and reversal learning deficits share a common neural substrate. To answer this question, we measured neural activity with in vivo calcium imaging in LOFC during compulsive grooming and reversal learning before and after fluoxetine treatment.

Methods: Sapap3-knockout (KO) mice were used as a model for OCD-relevant behaviors. Sapap3-KOs and wildtype (WT) littermates (KO: n = 8; 5 female; WT: n = 6; 3 female) were injected with virus encoding GCaMP6f (AAV5-synapsin-GCaMP6f-WPRE-SV40, titer 1.82x10^12) and implanted with gradient-index lenses to visualize LOFC activity using miniature microscopes. Grooming, reversal learning, and neural activity were measured pre- and post-fluoxetine treatment (18mg/kg, 4 weeks).

Results: In KOs, baseline increases in the number of grooming bouts (WT = 42 +/- 5: KO = 159 +/- 26; p < 0.003) and impairments in reversal learning as measured by the number of correct lever presses (WT = 68 +/- 7; KO = 33 +/- 10; p = 0.02) improved after fluoxetine treatment (Grooming bouts: KOpre = 159 +/- 26; KOpost = 107 +/- 24; p = 0.01; Reversal learning – correct lever presses: KOpre = 33 +/- 10; KOpost = 59 +/- 8; p = 0.04). Additionally, KOs displayed distinct patterns of abnormal LOFC activity during grooming and reversal learning, both of which normalized after fluoxetine. During grooming, baseline increases in the percentage of KO LOFC neurons inhibited by grooming (WT = 22.1 +/- 3.6%; KO: 32.1 +/- 1.6%; p = 0.02) decreased after fluoxetine (KOpre = 32.1 +/- 1.6%; KOpost = 25.3 +/- 1.8%; p = 0.001). During reversal learning, baseline decreases in the strength by which KO LOFC neurons were modulated by the correct lever press (WT = 0.33 +/- 0.03; KO = 0.27 +/- 0.02; p = 0.01) improved after fluoxetine (KOpre = 0.27 +/- 0.02; KOpost = 0.30 +/- 0.01; p = 0.01). Finally, encoding of reversal learning and compulsive behavior are independent, as reversal learning-associated neurons are distributed randomly amongst grooming-associated neurons (i.e. overlap is what would be expected by chance).

Conclusions: In OCD, the LOFC is disrupted during both compulsive behaviors and reversal learning, yet whether these behaviors share common neural underpinnings is unknown. We find that the LOFC plays distinct and independent roles in compulsive grooming and impaired reversal learning and their improvement with fluoxetine in a mouse model. These findings suggest that LOFC plays separate roles in pathophysiology and treatment of different perseverative behaviors in OCD.

Keywords: Obsessive Compulsive Disorder, In Vivo Calcium Imaging, Reversal Learning

Disclosure: Nothing to disclose.

P439. Effects of Rapid Face Stimuli Presentation on Dorsal and Ventral Visual Stream Connectivity in Body Dysmorphic Disorder

Wan-wa Wong, Rangaprakash Deshpande, Teena Moody, Natalie Rotstein, Jamie Feusner*

University of Toronto; Centre for Addiction and Mental Health, Toronto, Canada

Background: Body dysmorphic disorder (BDD) is marked by preoccupation with misperceived appearance flaws, causing individuals to believe that they are ugly and disfigured. Consequences are often severe, with high suicide attempt and hospitalization rates. Disturbances of visual information processing in BDD may be core neurobiological contributors to perceptual appearance distortions. Previous neuroimaging studies found abnormally reduced dorsal visual stream (DVS) activity when viewing images filtered to convey only configural/holistic information. These have contributed to a model of imbalances in global vs. local visual processing in BDD. In general, there is evidence that magnocellular pathways in the DVS are tuned to rapid presentation of images, thereby facilitating global/holistic visual processing. Moreover, with higher stimulus frequency/shorter stimulus duration, ventral visual stream (VVS) regions seem to reduce activation magnitude. Accordingly, we conducted a pre-translational investigation to determine the effects of rapid face presentation on DVS and VVS systems, responsible for global and local processing, respectively. Specifically, we investigated the effects on functional brain connectivity of viewing rapidly-presented, short-duration face stimuli in individuals with BDD and healthy controls, employing dynamic effective connectivity modeling.

Methods: Thirty-eight unmedicated adults with BDD and 29 healthy controls aged 18-40 participated. BDD participants met DSM-5 criteria for BDD, all with face concerns. Symptom severity was quantified with the Yale-Brown Obsessive-Compulsive Scale Modified for BDD (BDD-YBOCS), and the Brown Assessment of Beliefs Scale (BABS), assessing BDD symptoms and insight, respectively. Functional magnetic resonance imaging data were obtained while participants viewed photos of their own faces at different angles for short (125ms, 250ms, 500ms) and long (3000ms) durations.

Data preprocessing was done using fMRIPrep 1.4.0. Fourteen regions of interest (ROIs) in DVS and VVS were selected: 2 ROIs in primary visual cortex (V1) [bilateral calcarine], 6 ROIs in VVS [bilateral inferior occipital gyrus (IOG), fusiform gyrus (FG), and inferior temporal gyrus (ITG)], and 6 ROIs in DVS [bilateral superior occipital gyrus (SOG), inferior parietal gyrus (IPG), and superior parietal gyrus (SPG)]. Hemodynamic deconvolution was performed on the ROIs timeseries to minimize intra-subject hemodynamic response function variability, and to improve the estimation of effective connectivity. Dynamic effective connectivity, a dynamic measure of directional connectivity between pairs of ROIs, was computed at each time point using Kalman-filter based time-varying Granger causality. Twelve intra-hemispheric connections were chosen and divided into 4 categories: 1) VVS Lower (Calcarine to IOG), 2) VVS Higher (IOG to FG; IOG to ITG), 3) DVS Lower (Calcarine to SOG), and 4) DVS Higher (SOG to IPG; SOG to SPG). Linear mixed model was used to analyze the data (fixed factors: group [BDD or healthy controls], duration [125ms, 250ms, 500ms or 3000ms], category [VVS Lower, VVS Higher, DVS Lower or DVS Higher]; random factor: participant). For the follow-up pairwise comparisons, p-values were Bonferroni corrected. Spearman correlation was used to determine associations between dynamic effective connectivity and symptom severity measures of BDD-YBOCS and BABS in BDD participants.

Results: BDD individuals exhibited weaker dynamic effective connectivity than controls in DVS Higher during all stimuli presentation durations (125ms: p = 0.085; 250ms: p = 0.004; 500ms: p = 0.003; 3000ms: p = 0.064). There were no significant between-group differences for the other connectivity categories (i.e. DVS Lower, VVS Lower, and VVS Higher). Considering the within-group analyses, controls exhibited weaker dynamic effective connectivity for VVS Lower during short duration compared to during long duration (125ms < 3000ms, p = 0.018; 500ms < 3000ms, p = 0.007). Further, controls showed weaker dynamic effective connectivity for DVS Higher during the 125ms duration compared to during the 250ms duration (125ms < 250ms, p = 0.018). BDD showed weaker dynamic effective connectivity for DVS Lower during 125ms duration compared to during 500ms duration (125ms < 500ms, p < 0.001). Yet, there were no significant within-group differences for DVS between short and long durations. There was a significant negative correlation between BABS and dynamic effective connectivity during the long (3000ms) duration for DVSHigher (rho = -0.335, p = 0.040); those with weaker connectivity in the DVS Higher had poorer insight.

Conclusions: Those with BDD have aberrant, weaker connectivity in higher regions of the dorsal visual stream while viewing their faces. The clinical relevance of this pattern is underscored by the observation that those with poorer insight had weaker DVS connectivity during long duration viewing of their faces. There was no direct evidence that rapid face presentation using the parameters tested in this study enhances DVS connectivity, responsible for global/holistic visual processing. Nevertheless, the within-group results in healthy controls provide promise that rapid face presentation could potentially suppress VVS connectivity, responsible for local/detailed visual processing. For similar effects to occur in BDD, different parameters such as a higher number of stimuli may be necessary and will be explored in future studies.

Keywords: Body Dysmorphic Disorder, Visual Modulation, Dorsal Visual Stream, Ventral Visual Stream, fMRI Effective Connectivity

Disclosure: NOCD, LLC: Consultant (Self)

P440. Obsessive Compulsive Disorder During the COVID-19 Pandemic

Michael Van Ameringen*, Beth Patterson, Jasmine Turna, Carolina Goldman Bergmann, Nina Lamberti, Beth Sideris, Ana Paula Francisco, Heather Dwyer, Maryam Rahat, Stefano Pallanti, Giacomo Grassi, Bernardo Dell’Osso, Matteo E.M. Vismara, Umberto Albert, Eric Hollander, Jamie Feusner, Roseli Shavitt, Carolyn Rodriguez, Pedro Morgado, Naomi Fineberg

McMaster University, Hamilton, Canada

Background: The impacts of the COVID-19 pandemic have been legion in all corners of the globe. The impact on mental health has been well-documented and evidence continues to emerge. Obsessive-compulsive disorder (OCD) affects 1%–3% of the general population [1]. It is a chronic condition and is associated with significantly lower quality of life and major societal costs, [1]. OCD is characterized by unwanted and intrusive thoughts, images, or urges (obsessions) and repetitive behaviours (compulsions) [2]. A significant cluster of OCD symptoms includes fear of contamination, which often triggers ritualized hand-washing and other cleaning rituals in order to neutralize the thought [3]. The primary psychological treatment for OCD is Exposure and Response Prevention (ERP), which, in the case of contamination typically involves exposure to the thought of being contaminated and not engaging in the washing/cleaning rituals [3]. Recent reports have indicated that individuals with OCD may be particularly vulnerable to the mental health impact of the pandemic [4]. The widespread public health demands for increased and ‘proper’ hand-washing techniques, cleaning, and encouragement to use disinfectants as a result of the COVID-19 pandemic, may have been confusing for patients with OCD [5]. However, survey studies assessing the impact of the COVID-19 pandemic on OCD symptoms have yielded contrasting results, with some studies indicating no change and others indicating a worsening of OCD symptoms. The current cross-sectional study aims to comprehensively examine the psychological impact of the pandemic on individuals who suffered from OCD during the first phase of the COVID-19 pandemic across 3 continents: North America (NA), South America (SA) and Europe.

Methods: Adults aged 16 and over with a diagnosis of OCD, completed an online survey. Surveys were posted between May, 2020 and July, 2021 in English, Italian and Portuguese. After signing an electronic informed consent, completed a questionnaire battery, containing the Obsessive-Compulsive Inventory, Short Version (OCI-R) to assess OCD symptom severity, the Generalized Anxiety Disorder-7 (GAD-7) to assess anxiety severity, Patient Health Questionnaire (PHQ-9) to assess depression severity and the Sheehan Disability Scale to evaluate functional impairment. The impact of social supports and demographic variables on psychiatric symptoms and general behaviour of OCD individuals during the COVID-19 pandemic was also examined. Validated cut scores on the GAD-7, PHQ-9 and OCI-R were used to estimate rates of GAD, Major Depressive Disorder (MDD) and OCD. Contamination symptoms were evaluated using the Washing subscale of the OCI-R [6]; a score of ≥ 8 was considered high. Statistical methods included descriptive statistics, ANCOVA and logistic regression analyses.

Results: The survey was completed by 417; 75% female, with a mean age of 31.4 ± 11.3. Most were from NA (56%), (SA: 22%; Europe: 22%). The mean scores on all symptom severity scales were above the clinical threshold, including the OCI-R: 28.9 ± 12.4, with no significant differences found between continents on ANCOVA. Most (76%) reported a worsening of their OCD symptoms during the first wave of the pandemic, with increases in both intrusive thoughts and rituals. Nearly 70% reported current OCD treatment (56% medication 43% psychotherapy) and 45% of this group reported increasing their treatment dose or frequency during the pandemic. Predictors of worsening OCD included being younger than 40 (p < .01), having comorbid GAD or MDD (p < .001) and having high contamination symptoms, (p < .01), while being from Europe was associated with decreased risk of worsening symptoms (p < .05). The symptom severity scale scores for individuals with high contamination were significantly higher even when controlling for demographic factors, including continental residence via ANCOVA. Those with high contamination also reported significantly less perception of emotional support, more anxiety about contracting and transmitting COVID-19 or a loved one contracting COVID-19.

Conclusions: In this international sample of OCD individuals, most perceived a worsening of their OCD symptoms during the pandemic, as evidenced by the 45% who increased their psychological or pharmacological treatment. Although no differences were found across continents in terms of OCD severity, having European residency was associated with a decreased risk of perceived worsening of symptoms. This may be attributed to the timing of survey, such that COVID-19 cases were decreasing in Europe, while North and South America were at the height of the first wave.

Keywords: OCD, COVID-19, Comorbidity

Disclosure: Biohaven: Contracted Research (Self)

P441. ACC-striatal Projections are Uniquely Positioned to Interact With an Unusually Functionally Diverse Set of Cortical Areas

Claudio Toro-Serey*, Wei Tang, Lucas Trambaiolli, Peter Dayan, Suzanne Haber

McLean Hospital, Harvard Medical School, Belmont, Massachusetts, United States

Background: Cortico-striatal projections play a central role in providing the basal ganglia with integrated information relevant to action selection and execution, making them a key candidate for the treatment of goal-directed and habitual disorders such as addiction and OCD. Probabilistic models have successfully summarized the spatial topography of this circuitry (Averbeck et al., 2014). For example, projections originating caudally from motor control areas terminate in the dorsolateral striatum, whereas rostral projections from ventromedial prefrontal cortex (PFC) terminate in ventromedial striatum. However, unlike the dorsolateral and ventromedial striatal sectors, the rostral and central striatum receives converging projections from multiple areas. This region is particularly complex and serves as an interface between functionally diverse cortical regions, the orbitofrontal cortex (OFC), ventrolateral PFC (vlPFC), and anterior cingulate cortex (ACC). Although there is an underlying topography to these connections, this alone may not be sufficient to understand the complexity of their interactions. The ACC is a particularly good example with its functional diversity and distributed striatal projections. The goal of this study was to develop a data-driven methodology that works in tandem with the more traditional topographic approach, to uncover additional key organizational principles of cortico-striatal circuitry. We focus specifically on the relationship between ACC-striatal projections to those originating in other areas of PFC.

Methods: We analyzed 30 anterograde injections sites evenly distributed throughout macaque PFC (Averbeck et al., 2014). For each injection, we tabulated the loci of its terminal projections according to a striatal grid composed of 600 μm isotropic voxels. We then computed the similarity of the projections among every pair of cortical injections using a metric that corrects for chance agreement (adjusted rand index), and clustered cortical regions using spectral methods on the resulting similarity matrix. This identified two dominant gradients of cortical organization. We then visually examined the pattern of projections of every cortical cluster. Finally, based on previous qualitative observations that PFC projections to the striatum are mirrored along a dorso-ventral axis in ACC (Tang et al., 2019), we asked whether PFC regions could be similarly organized based on their connectivity to this region. We replicated the clustering analysis using 10 cortico-cortical retrograde injections distributed along the ACC. For each injection site, we computed the proportion of cells that projected to it from each area in PFC, and clustered cortical areas by the similarity of their projection pattern across injection sites.

Results: The primary gradient organized cortical areas based on the location of their terminal projections along a ventromedial to dorsolateral axis in striatum. The secondary gradient captured the size of these projections. In line with classic topographic findings, the combined gradients positioned areas in ventromedial PFC as focally projecting to ventromedial striatum, whereas motor and dorsal PFC areas projected focally to dorsolateral striatum. In contrast, regions in ACC and portions of OFC had broad projections in central striatum, displaying partial overlap with the two more focal clusters. We found no significant relationship among injection volume, size of terminal projections, or the mean similarity of a given area (all pairwise correlations p > 0.1). Clustering performed on retrograde ACC injections resulted in a comparable primary gradient in PFC; motor and limbic areas primarily projected to dorsal and subgenual ACC, respectively, with remaining areas mostly projecting to rostral ACC.

Conclusions: In this project, we used a data-driven approach to further characterize the underlying organizational principles of cortico-striatal circuitry. We used this approach and identify that ACC stands out in its connectivity within this network. We show that projections to striatum are organized by the size of their terminal fields in addition to their rostro-caudal location. The combination of these axes of organization distinguished ACC as an area with particularly widespread connections to the striatum. These results were not explained by methodological issues, such as injection volume. Further, we note commonalities between the organization of connections between prefrontal areas and both the ACC and the striatum. Based on these findings, we conclude that the ACC integrates information from diverse functional areas and relays this information to other functional groups via its relatively large projections to striatum. The mirrored cortico-cortical organization observed here raises the possibility that an individual’s topography of cortico-striatal projections, which can be difficult to precisely map using neuroimaging methods, could be approximated using cortico-cortical connectivity with ACC. This possibility could facilitate the identification of cortical targets for transcranial stimulation. Future work will test these findings using networks derived from diffusion and functional MRI in human and non-human primates.

Keywords: Neuroanatomy, Cortico-Striatal Connectivity, Anterior Cingulate Cortex (ACC), Connectivity Gradients

Disclosure: Nothing to disclose.

P442. Similar Valence Processing Alterations Associated With Compulsive Behavior in SAPAP3 Knockout Mice and Human OCD

Bridget Kajs*, Peter J. van Roessel, Gwynne L. Davis, Leanne M. Williams, Carolyn I. Rodriguez, Lisa A. Gunaydin

University of California, San Francisco, San Francisco, California, United States

Background: Abnormalities in valence processing – the processing of aversive or appetitive stimuli – may be an underrecognized component of obsessive-compulsive disorder (OCD). Independent experimental paradigms have suggested disturbance of emotional valence systems in OCD, yet there is a dearth of studies assessing both negative and positive valence processing in clinical studies of OCD patients, either at baseline or in response to therapeutic interventions. Additionally, preclinical rodent models are critical for treatment discovery in OCD, yet investigations examining whether rodent models of compulsive behavior similarly show alterations in valence systems have been limited. In this study, we assessed valence processing in both human OCD patients and a preclinical rodent model of compulsive behavior, the SAPAP3 knockout (KO) mouse model.

Methods: In OCD patients (N = 41), we utilized a standardized, computer-based cognitive testing platform to examine both explicit (conscious) and implicit (nonconscious) processing of fear-related facial expressions (negative valence) and socially-rewarding happy expressions (positive valence). Subject-level performance was quantified with reference to age-, biological sex-, and years of education-matched norms derived from a previously acquired healthy norm cohort (N = 1317) and assessed in relation to clinical measures including the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) and Depression Anxiety Stress Scales (DASS). In the SAPAP3 KO mouse model of compulsive behavior, we used auditory fear conditioning and extinction in SAPAP3 KO mice (N = 11) and wild-type (WT) littermate controls (N = 11) to assess alterations in negative valence processing. We additionally used reward-based operant conditioning in SAPAP3 KO mice (N = 8) and WT littermate controls (N = 11) to assess alterations in positive valence processing. Both sexes were included in both the human and rodent studies.

Results: OCD patients were found to have speeded (Wilcoxon Rank Sum Test, p = 0.025) and more accurate (Wilcoxon Rank Sum Test, p < 0.001) identification of fearful compared to happy facial expressions on the explicit emotional processing task. On the implicit emotional processing task, OCD patients were significantly less accurate at identifying previously seen faces when implicitly influenced by fearful expressions compared to happy expressions (Wilcoxon Rank Sum Test, p < 0.0001). Speeded explicit responses to fearful expressions were correlated with greater subjective anxiety (Spearman’s correlation, rho = 0.46, p = 0.003) while decreased facial recall accuracy under the implicit influence of fearful relative to happy expression correlated with OCD severity by Y-BOCS (Spearman’s correlation coefficient, rho = -0.38, p = 0.015). SAPAP3 KO mice showed enhanced fear learning and impaired fear extinction as evidenced by increased freezing compared to WT mice during both fear conditioning (Two-way Repeated Measures ANOVA, Time x Genotype p < 0.05, Time p < 0.0001, Genotype p = 0.0001) and extinction (Two-way Repeated Measures ANOVA, Time x Genotype p < 0.01, Time p < 0.0001, Genotype p < 0.0001). In reward-based operant conditioning, SAPAP3 KO mice were significantly slower than wild-type mice at acquiring positive-reinforced nose-poke behavior (Two-way Repeated Measures ANOVA, Genotype x Training Day p < 0.0001, Training Day p < 0.0001, Genotype p < 0.0001) and were unable to maintain goal-directed responding for rewards (Two-way Repeated Measures ANOVA, Genotype x Training Day p < 0.0001, Training Day p < 0.0001, Genotype p < 0.0001).

Conclusions: We find that OCD patients and SAPAP3 KO mice both show evidence of enhanced negative valence processing and impaired positive valence processing. Our results reveal similar valence processing abnormalities in OCD patients and a preclinical rodent model of compulsive behavior, which suggest valence processing alterations as novel therapeutic targets across a translational research spectrum.

Keywords: Negative Valence, Positive Valence, OCD, SAPAP3 KO Mice

Disclosure: Nothing to disclose.

P443. Tolcapone in Obsessive Compulsive Disorder: A Randomized Double-Blind Placebo-Controlled Crossover Trial

Jon Grant*, Samuel Chamberlain

University of Chicago, Chicago, Illinois, United States

Background: Despite the availability of evidence-based treatments for obsessive-compulsive disorder (OCD), not all patients experience sufficient benefit or are able to tolerate them. Tolcapone is a catechol-o-methyl-transferase (COMT) enzyme inhibitor that augments cortical dopaminergic transmission. Conduct a proof of concept study to examine whether a COMT inhibitor would reduce OCD symptoms to a greater extent than placebo.

Methods: We conducted a randomized, placebo-controlled, double-blind cross-over trial in adults with OCD (N = 20). This was a fully counter-balanced, double-blind, placebo-controlled cross-over design in which participants received EITHER tolcapone 100mg twice daily for two weeks, followed by one-week washout, followed by placebo twice daily for two weeks; OR placebo twice daily for two-weeks, followed by one-week washout, followed by tolcapone 100mg twice daily for two weeks. The order of treatment was randomized. The washout period was intended to prevent possible carryover effects that might compromises the assessments and conclusions. The study had low risk of bias using the Cochrane criteria. Because tolcapone at these lower doses has few side effects, a cross-over design was considered as side effects should not jeopardize the blinding. The analysis followed Intent-To-Treat principles, with Last-Observation-Carried-Forward for dropouts and missing data. The analytic approach was determined prior to data unlock. Changes in YBOCS total scores for placebo treatment and tolcapone treatment were compared using paired sample t-tests, which constituted the primary analysis. This method was appropriate because the design was fully counter-balanced and randomized. Changes in total depression and anxiety symptom scores, and disability, were examined, again using paired t-tests, as secondary analyses. Statistical significance was defined as p < 0.05 two-tailed.

Results: When taking tolcapone, participants experienced a mean decrease in their total YBOCS scores of -4.24 (SD = 6.20), which differed significantly from the change observed under placebo treatment of -1.10 (SD = 4.71) (t = 2.194, df = 19, p = 0.0409). The mean percentage decreases in the total YBOCS scores for the entire sample over the corresponding two-week periods were 16.4% for tolcapone and 3.6% for placebo.

Conclusions: This randomized, placebo-controlled cross-over trial indicated that two-week treatment using tolcapone (100mg twice daily) was associated with significant symptomatic improvement in OCD as compared to two-week administration of placebo. The likely mechanism is that tolcapone enhanced cortical dopamine transmission and therefore top-down executive control over habitual patterns of behavior. The finding of significant separation from placebo after two weeks may suggest that longer studies using tolcapone for OCD may be worthwhile to see if even greater benefit is possible. This small study was intended merely to see if tolcapone produced a signal and therefore would merit further study.

Keywords: COMT Inhibitor, Obsessive-Compulsive Disorder (OCD), Pharmacotherapy

Disclosure: Otsuka, Biohaven: Grant (Self)

P444. Different Brain Activation in Patients With OCD Compared to Healthy Participants During Conditioning: An fMRI Fear Extinction Paradigm

Juliana Diniz, Paulo Bazán, Carlos Alberto Pereira, Erlandson Saraiva, Paula Ramos, Amanda Oliveira, Adriano Reimer, Marcus Brandão, Marcelo Hoexter, Roseli Shavitt, Euripedes Miguel, Marcelo Batistuzzo*

Psychiatric Institute HC-FMUSP, Sao Paulo, Brazil

Background: Patients with obsessive-compulsive disorder (OCD) have shown a fear processing pattern characterized by partial or total failure to recall extinction and hypoactivation of the ventromedial prefrontal cortex during early recall. Also, increased fear renewal was observed in a drug-free sample of OCD patients compared with their healthy counterparts. However, the brain activation underlying those processes is not well established, especially during the renewal phase, and studies investigating patterns of brain activation during fear conditioning/extinction tasks are warranted. Our main objective was to compare the behavior performance and brain activation during fear processing between adult, symptomatic and drug-free patients with OCD and healthy participants (HP) in a fear conditioning/extinction paradigm. We expected to replicate previous findings regarding worse extinction retention in a sample of drug-free OCD patients.

Methods: We measured skin-conductance (SCR) and blood oxygenation level-dependent response (BOLD) obtained in a 3T Philips Achieva scan in 37 drug-free adult OCD patients with current symptoms of moderate severity and 32 HP matched according to biological sex and age. Participants underwent a two-day, event-related, fear-conditioning fMRI paradigm comprising four different phases: conditioning and extinction (day 1), and recall and renewal (day 2). The tactile aversive (unconditioned) stimulus was an electric shock.

The paradigm was developed by Milad et al. (2013): there are two contexts (pictures of different rooms): one for conditioning and renewal, and another for extinction and recall. In these contexts, the visual cues (lights in one of the three basic colors) are presented. Cues are classified as conditioned to shock (CS+) or not conditioned to shock (CS-). There are two types of CS + , one of them is extinguished (CS + E) while the other is not (CS + U). For analytical purposes, the CS-s were divided into CS-E when paired with CS + E or CS-U when paired with CS + U, even though both CS-s correspond to the same stimulus.

The fear response (SCR) was measured through electrodermal activity (Biopac® Systems) and was determined as the difference between the maximum skin conductance level (SCL) reached during the 6s of CS presentation and the minimum skin conductance level during the 2s prior to context presentation.

Whole-brain BOLD contrasts included: the average maps for each group on each phase; a between-groups two-sample t-test (for each phase), and comparisons between the contexts in all four phases using two-way ANOVA, evaluating the effects of phase and its interaction with group comparing the phases two-by-two. Probability maps were generated using a stringent voxel threshold of Z > 3.1 and a (corrected) cluster p < 0.05.

Patients and HP were evaluated by experienced psychologists or psychiatrists that collected demographic information and applied the SCID-IV, supplemented with modules for tic and impulse control disorders. In addition, OCD patients were evaluated with the following clinical structured instruments: the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), the Dimensional Y-BOCS, the Beck Depression and Anxiety Inventories.

Results: There were no significant group differences regarding SCR signal quality (X2 = 1.45, p = 0.23) or response congruence with stimuli (X2 = 0.02, p = 0.88). Both groups presented effective fear conditioning, and there were no between-group differences regarding the prevalence of CS learning (X2 = 2.05, p = 0.15). Across all phases, OCD patients presented higher SCR than HP for all types of stimuli.

Significant group differences were detected in fMRI analyses during conditioning, in the contrast between late conditioned stimuli (last four presentations of the CS + E) and unconditioned stimuli (CS-): a cluster encompassing inferior frontal, superior temporal, and pre and post-central gyri (Zmax = 4.54, p < 0.0001). There were also significant between-group differences in response to late CS + E (compared with baseline) during conditioning in regions of the right hemisphere, presented in three clusters, including the pre and post-central gyri and inferior frontal gyrus (Zmax = 4.14, p = 0.001), the insular cortex, and putamen (Zmax = 4.17, p = 0.009), and the lingual gyrus (Zmax = 4, p = 0.016). In addition, during late extinction, OCD patients presented higher activation of the left fusiform gyrus (CS + E late: Zmax = 4.04, p = 0.014). There were no significant differences between groups in early phases of conditioning or extinction, nor in early or late phases of recall or renewal.

Conclusions: Different patterns of brain activation during fear conditioning could explain differences in behavior between OCD patients and HP. Also, regions associated with OCD psychopathology and recognition of painful and visual emotional stimuli may participate in fear learning and extinction and may affect the expression of fear responses during recall and renewal. These findings underscore the relevance of the interaction between OCD psychopathology and fear processing. Future studies should investigate the relevance of contextual information in the processes of fear learning, extinction recall, and fear renewal in OCD patients.

Keywords: Obsessive-Compulsive Disorder (OCD), Functional Neuroimaging, Fear Physiology, Fear Conditioning and Extinction

Disclosure: Nothing to disclose.

P445. The Genetic Architecture of Obsessive-Compulsive Disorder: Alleles Across the Frequency Spectrum Contribute Liability to OCD

Behrang Mahjani, Lambertus Klei, Manuel Mattheisen, Matthew Halvorsen, Abraham Reichenberg, Kathryn Roeder, Nancy Pedersen, Julia Boberg, Elles de Schipper, Cynthia Bulik, Mikael Landen, Bengt Fundin, David Mataix-Cols, Sven Sandin, Christina Hultman, James Crowley, Joseph Buxbaum, Christian Ruck, Bernie Devlin, Dorothy Grice*

Icahn School of Medicine at Mount Sinai, New York, New York, United States

Background: Obsessive-compulsive disorder (OCD) is known to be substantially heritable; however, the contribution of common genetic variation across the allele frequency spectrum to this heritability remains uncertain. We use two new, homogenous cohorts to estimate heritability of OCD from common genetic variation and contrast results with prior studies.

Methods: The sample consisted of 2090 Swedish-born individuals diagnosed with OCD and 4567 controls, all genotyped for common genetic variants, specifically >400,000 single nucleotide polymorphisms (SNPs) with minor allele frequency (MAF) ≥ 0.01. Using genotypes of these SNPs to estimate distant familial relationships among individuals, we estimated heritability of OCD, both overall and partitioned according to MAF bins.

Results: We estimated narrow-sense heritability of 29% (SE = 4%). The estimate was robust, varying only modestly under different models. Contrary to earlier reports, however, SNPs with MAF between 0.01 and 0.05 accounted for 10% of heritability and estimated heritability per bin roughly follows expectations based on a simple model for SNP-based heritability.

Conclusions: These results indicate that common inherited risk variation (MAF ≥ 0.01) accounts for most of the heritable variation in OCD. SNPs with low MAF contribute meaningfully to the heritability of OCD and the results are consistent with expectation under the “infinitesimal model,” where risk is influenced by a large number of loci across the genome and across MAF bins.

Keywords: Genetic Architecture, SNP Variation, Rare Genetic Variation

Disclosure: Nothing to disclose.

P446. Developmental Impact of Glutamate Transporter Overexpression on Dopaminergic Neuron Activity and Stereotypic Behavior

Muhammad Chohan*, Jared Kopelman, Hannah Yueh, Zeinab Fazlali, Natasha Greene, Alexander Harris, Peter Balsam, E. David Leonardo, Edgar Kramer, Jeremy Veenstra-Vanderweele, Susanne Ahmari

Columbia University,New York State Psychiatric Institute, New York, New York, United States

Background: Obsessive-compulsive disorder (OCD) is a disabling condition that often begins in childhood. Genetic studies in OCD have pointed to SLC1A1, which encodes the neuronal glutamate transporter EAAT3, with evidence suggesting that increased expression contributes to risk. In mice, midbrain Slc1a1 expression supports repetitive behavior in response to dopaminergic agonists, aligning with neuroimaging and pharmacologic challenge studies that have implicated the dopaminergic system in OCD. These findings suggest that Slc1a1 may contribute to compulsive behavior through altered dopaminergic transmission; however, this theory has not been mechanistically tested. To examine the developmental impact of Slc1a1 overexpression on compulsive-like behaviors, we therefore generated a novel mouse model to perform targeted, reversible overexpression of Slc1a1 in dopaminergic neurons.

Methods: Slc1a1-tetO mice were crossed to the Th-tTA line to obtain Slc1a1-Th-overexpressing (OE) and control mice. EAAT3 expression was regulated by doxycycline-supplemented chow (400mg/kg) and was quantified using real-time qRT-PCR and immunoblots. Mice were evaluated for baseline anxiety-like and repetitive behaviors (elevated plus maze, light-dark emergence, and marble-burying), AMPH-induced locomotion and stereotypy, and for D1-agonist (SKF-38393)-induced grooming behavior. Dopamine transmission was evaluated using single unit dopamine neuron recordings in anesthetized mice and via fiber photometry using the dLight1.1 dopamine sensor in behaving mice. Adult male and female mice and littermate controls were used for all experiments.

Results: Mice with life-long overexpression of Slc1a1 showed a significant increase in amphetamine-induced stereotypy (8.0 mg/kg, 3-way RM ANOVA; drug x genotype interaction, F (1, 38) = 13.89, P = 0.0006; genotype, F (1, 38) = 9.839, P = 0.0033, n = 11-10) and hyperlocomotion (3.0 mg/kg, curve-fit; F (4, 370) = 16.33, P < 0.0001, n = 11-10). Single-unit recordings demonstrated that Slc1a1 overexpression was associated with increased firing of dopaminergic neurons (spikes fired in bursts, unpaired t (10) = 4.684, P = 0.0009, firing rate, unpaired t (10) = 3.808, P = 0.0034, n = 6-6). Furthermore, dLight1.1 fiber photometry showed that these behavioral abnormalities were associated with increased dorsal striatum dopamine release both at baseline (unpaired t (9) = 3.379, P = 0.0081, n = 5-6) and following amphetamine (3.0 mg/kg) (unpaired t (8) = 5.065, P = 0.0010, n = 5-5). In contrast, no impact of overexpression was observed on anxiety-like behaviors or SKF-38393-induced grooming. Importantly, overexpression solely in adulthood failed to recapitulate these behavioral phenotypes, suggesting that overexpression during development is necessary to generate pathology. However, doxycycline-induced reversal of Slc1a1/EAAT3 overexpression in adulthood normalized both the increased dopaminergic firing and AMPH-induced responses.

Conclusions: Our data suggest that alterations in dopaminergic transmission during development may be a mechanism underlying the effects of Slc1a1/EAAT3 overexpression, warranting additional work to understand the dynamics of glutamatergic and dopaminergic signaling in basal ganglia circuits during early developmental periods. Our electrophysiological and behavioral data following reversal of EAAT3 overexpression suggest that EAAT3 inhibitors should be evaluated as a potential treatment for basal ganglia-mediated repetitive behavior.

Keywords: Glutamate Transporter (EAAT3), Dopamine, Sensitive Period, Fiber Photometry, Amphetamine

Disclosure: Nothing to disclose.

P447. EFP-Neurofeedback in Adolescents With Borderline Personality Disorder: A Proof-Of-Concept Trial

Christian Paret*, Malte Zopfs, Jackob Keynan, Miroslava Jindrová, Madita Stirner, Sarah Baumeister, Pascal Aggensteiner, Daniel Brandeis, Talma Hendler, Christian Schmahl

Central Institute of Mental Health, University of Heidelberg, Mannheim, Germany

Background: Neurofeedback can teach patients to regulate brain activity. Targeting the amygdala for neurofeedback training to improve emotion regulation could be an effective adjuvant treatment for patients suffering from Borderline Personality Disorder (BPD). The scalability of functional magnetic resonance imaging (fMRI) amygdala-neurofeedback could be significantly increased by advancing to fMRI-informed electroencephalography (EEG) signatures such as the amygdala Electrical Fingerprint (EFP). The aim of this study is to assess the feasibility and validity of amygdala-EFP neurofeedback-training in adolescent BPD patients undergoing therapy.

Methods: 28 adolescents with BPD (14 in the treatment group) undergoing residential Dialectical-Behavior-Therapy (DBT) were assessed in this open-label neurofeedback-study. EFP provides an EEG surrogate of deep brain activation optimized to predict the amygdala Blood Oxygenation Level dependent (BOLD) signal. The treatment group received 10 EFP-neurofeedback training sessions over 5 weeks, while the treatment-as-usual control group did not receive any training. An acoustic brain-computer interface was used for training, where the subject voluntarily decreased the volume of a melody representing EFP activation. The study began and ended with an MR-Scan that included brief amygdala-BOLD-neurofeedback to analyze improvement of amygdala regulation. In MR sessions, feedback was given visually via a thermometer-like display. Simultaneous EEG-fMRI data were recorded in the last MR-session to determine whether the amygdala-EFP predicts the amygdala-BOLD signal. FMRI data from the pre- and post-training session were used to quantify transfer of learned EFP-regulation to veridical amygdala-BOLD regulation (i.e., target engagement test). The simultaneous EEG-fMRI data from the last session were used to quantify correlation of the EFP with the fMRI BOLD signal (i.e., validation of EFP). FMRI data were preprocessed with the open software fMRIPrep. Statistical parametric modeling analysis was applied to analyze amygdala down-regulation in the a-priorily defined amygdala region of interest. The fMRI analysis to validate the EFP was done with family-wise error correction with p < 0.05 at the voxel-level in the whole brain. Self-report measures (Toronto Alexithymia Scale, Beck Depression Inventory, Borderline Symptom List short version, Affect Lability Scale) and participant drop-out were assessed for clinical effects and feasibility assessment. The study is registered at clinicaltrials.gov, NCT03964545.

Results: Significant improvements in both groups were found for the Beck Depression Inventory (F = 8.99, p = 0.006) and Affect Lability Scale (F = 7.08, p = 0.014), but not for the Toronto Alexithymia Scale and the Borderline Symptom List (p > 0.05). Study drop-out was 40%, of which 60% were due to leaving therapy early. Final MRI- and EEG-analysis results were on the way at abstract submission and will be presented on the conference poster.

Conclusions: Attrition due to premature discharge from residential treatment is important to consider for future neurofeedback trials in this setting. As DBT is an effective treatment, clinical improvements exceeding the therapy effect are difficult to achieve with adjuvant interventions. Ideally, outcomes for adjuvant neurofeedback will be defined on a mechanistic level rather than as psychopathology measures, as the latter do not leave much space for improvement on top of DBT. The verification of amygdala-targeting with EFP in BPD is critical to advance to a randomized clinical trial.

Keywords: Amygdala, Neurofeedback, Borderline Personality Disorder

Disclosure: Nothing to disclose.

P448. Prefrontal Cortex Engagement During an fMRI Task of Emotion Regulation as a Potential Predictor of Antidepressant Treatment Response in Borderline Personality Disorder

Christina Michel*, J. John Mann, Noam Schneck, Barbara Stanley

Columbia University, New York State Psychiatric Institute, New York, New York, United States

Background: Borderline personality disorder (BPD) is a severe mental illness affecting over four million individuals in the United States. Emotion dysregulation is a core feature underlying BPD. While prior work has examined the neural underpinnings of emotion dysregulation in BPD, little is known about how this relates to treatment response. The present study examines how baseline blood oxygen level dependent (BOLD) activation during a functional magnetic resonance imaging (fMRI) task of emotion regulation is related to antidepressant response following six months of Dialectical Behavior Therapy (DBT) or Selective Serotonin Reuptake Inhibitor (SSRI) treatment.

Methods: Individuals with BPD reporting a history of suicidal behavior or suicidal ideation (N = 37) underwent an fMRI task on a 3T GE scanner in which they were asked to either distance (i.e., downregulate their emotional response) or immerse (i.e., freely experience emotions) when recalling aversive personal memories. Patients were then randomized to six months of either DBT (N = 17) or SSRI (N = 20) treatment. Baseline and post-treatment measures of depression severity, affect lability and suicidal ideation were obtained. BOLD signal was analyzed using FSL and analyses of brain-wide voxel effects were thresholded at voxel (p < 0.001) and cluster (p < 0.05).

Results: When including treatment type as a covariate and controlling for baseline depression scores, neural activation during distancing was associated with treatment change in depression severity. In the SSRI group, greater activation in a cluster containing the orbital frontal cortex (OFC), frontal pole, and inferior frontal gyrus was associated with lower BDI scores at 6 months, indicating more improvement, while less activation during distancing was associated with higher BDI scores, indicating poorer outcomes. The opposite was seen in the DBT group, with greater activation in this cluster associated with less improvement.

Conclusions: Prior research suggests engagement of prefrontal regions during emotion regulation is associated with more effective regulation and greater cognitive control. The findings of this study indicate that individuals with greater prefrontal engagement at baseline experience a greater reduction in depressive symptoms when receiving SSRI treatment but the opposite for DBT. Further research is needed to understand how neural activation during emotion regulation may predict whether fluoxetine or DBT is a more effective antidepressant treatment for individual patients with BPD. The opposite direction of the relationships suggest that this effect is related to treatment response and not a nonspecific correlate of improvement independent of treatment type.

Keywords: Functional MRI (fMRI), Borderline Personality Disorder, Psychotherapy, Antidepressants, Prefrontal Cortex

Disclosure: Nothing to disclose.

P449. Protein Aggregation in a Subset of Patients With Schizophrenia

Leslie Nucifora*, Matthew MacDonald, Koko Ishizuka, Brian Lee, Mark Haft, Akira Sawa, Christopher Ross, Robert Sweet, Frederick Nucifora

Johns Hopkins University School of Medicine, Baltimore, Maryland, United States

Background: Schizophrenia (SCZ) is a complex disorder, which complicates the understanding of the mechanisms underlying SCZ. Genetic mutations and environmental stressors can lead to abnormal proteins. One way to conceptualize a disorder as complex as SCZ is to identify a cellular process that could have broad implication in neuronal functioning that is tied to the way neurons handle abnormal proteins in general. Proteostasis and the ubiquitin proteasome system (UPS) are central to proper cellular functioning via control of protein synthesis, folding, protein interactions, trafficking and degradation. Abnormalities in this process would lead to improperly regulated proteins, which could be diverse. This could help explain the multitude of cellular dysfunction and symptoms seem in SCZ. The failure of the cell to handle abnormal proteins results in protein insolubility. Ubiquitin is a marker for protein insolubility, and is found in the insoluble fraction of brain disorders with protein insolubility. Recently, attention has focused on the role ubiquitin and the UPS has in SCZ, with studies suggesting dysregulation at the genetic and protein level. The UPS and protein insolubility may provide the potential opportunity to understand how environmental stressors and genetic mutations relate to SCZ. Furthermore, sequestration of critical proteins that are prone to aggregation can lead to neuronal dysfunction.

Methods: Prefrontal cortex or superior temporal gyrus from autopsy brains obtained from the University of Pittsburgh, University of Texas, and Harvard Brain Banks, and olfactory neurons obtained from living subjects from the Johns Hopkins Schizophrenia Center were processed using a fractionation protocol designed to extract the proteins into insoluble and soluble fractions. Levels of protein insolubility and ubiquitin reactivity, markers for protein aggregation, were quantified after SDS-PAGE separation followed by Coomassie staining and Western blot analysis and normalized to total homogenate protein. Mass spectrometry was performed in order to identify the protein composition in the insoluble fraction. Gene Ontology Enrichment Analysis and Ingenuity Pathway Analysis were used to assess the potential biological relevance of the detected proteins in the insoluble fraction.

Results: A subset of patients with schizophrenia showed an increase in markers for protein

aggregation, specifically protein insolubility and ubiquitination. Mass spectrometry of the insoluble fraction revealed that cases with increased insolubility and ubiquitination showed similar pattern of peptide clustering by principal component analysis. The proteins that were significantly altered in the insoluble pellet were enriched for proteins related to the UPS at every step in the process, as well as relating to axon target recognition and nervous system development and function. Furthermore, protein insolubility was demonstrated in a subset of patient’s olfactory neurons, providing the potential for clinical correlations.

Conclusions: This study demonstrates the pathological process of protein aggregation in a subset of patients with schizophrenia. Understanding the mechanisms related to protein aggregation in schizophrenia could lead to a better understanding of the disease process and novel therapeutic targets.

Keywords: Schizophrenia, Protein Aggregation, Ubiquitination, Proteostasis, Ubiquitin Proteasome System

Disclosure: Nothing to disclose.

P450. Genetic Moderators of Cognitive Predictors of Employment Status in Patients With Schizophrenia

Rachael Blackman*, Daniel Eisenberg, Dwight Dickinson, Michael Gregory, Karen Berman

National Institute of Mental Health, Intramural Research Program, Bethesda, Maryland, United States

Background: Among a number of factors that influence functional outcomes in patients with schizophrenia, the degree of cognitive impairment an individual manifests has been shown to be a key predictor. Prior work has demonstrated that IQ, a general measure of cognitive ability, is related to poor functional outcomes (including employment) in schizophrenia, but it remains unresolved whether this relationship might be driven by deficits in specific cognitive domains. Six cognitive domains (verbal memory, NBack working memory, visual memory, processing speed, card sorting/executive function, and span working memory) have been found to be separable, but correlated, factors that characterize somewhat distinct aspects of cognitive deficits in patients. Here, we examine whether and which of these factors predict employment outcomes. Additionally, as schizophrenia is highly heritable, and genetic factors play a role in heterogeneity of the disorder, we also investigated whether differences in polygenic risk levels moderate the relationship between cognition and employment outcomes. Understanding reliable and more specific predictors of functional outcome in the patient population is a necessary step toward developing priorities for cognitive treatment targets, and if genetic markers are influential then these may be an important step towards personalized medicine approaches.

Methods: Patients with schizophrenia spectrum disorders (n = 129; 98 with schizophrenia, 19 with schizoaffective disorder, and 12 with a psychotic disorder not otherwise specified; 41 female, 88 male; mean age 33.1 +/- 10.6 years) participated in an extensive research visit at the National Institute of Mental Health Intramural Research Program that included neuropsychological and genetic testing. Individuals were recontacted an average 8.8 (+/-4.3) years later to obtain information on functional outcome, including employment status (whether employed or unemployed). Logistic regressions using Wald chi-square testing (excluding retired individuals, n = 4) were used to test whether cognitive measures, including ‘g’ (a measure of general cognition), IQ (as measured by Wechsler Adult Intelligence Scale), and 6 cognitive domains (listed above; each factor being calculated based on patients’ performance on a battery of cognitive tests at their initial visit), were predictors of patients’ employment status at follow-up. Additionally, in a subset of patients (n = 104), we derived polygenic scores for schizophrenia risk (PGSscz) and cognitive ability (PGScog) based on summary statistics from published genome-wide association studies. Logistic regressions were repeated after including polygenic scores in the models, which identified whether genetic predisposition moderated each cognitive predictors’ effects on employment status.

Results: At follow-up, 43.8% of patients were employed. Employment at follow-up was associated positively with g (n = 111, B = 0.693, SE = 0.320, Wald = 4.709, p = 0.030), IQ (n = 112, B = 0.061, SE = 0.022, Wald = 7.492, p = 0.006), and verbal memory (n = 111, B = 0.475, SE = 0.214, Wald = 4.925, p = 0.026) such that individuals with higher scores on these cognitive measures were more likely to be employed. Other cognitive subdomains were not significantly associated with employment status. When considering whether PGSscz is a potential moderator of cognitive performance effects, we found an NBack working memory-by-PGSscz interaction effect (n = 81, p = 0.044) on employment status as well as a processing speed-by-PGSscz interaction effect (n = 92, p = 0.038) on employment status. The processing speed-by-PGSscz interaction effect indicated that, in patients with higher PGSscz, higher processing speed scores were associated with a higher likelihood of employment. This was not the case in the patients with lower PGSscz where there was no meaningful difference between processing speed scores and whether or not someone was employed at follow-up. The NBack working memory-by-PGSscz interaction effect was similar in magnitude, but harder to interpret. However, the PGScog was not found to moderate the relationship of cognitive measures and employment status.

Conclusions: Overall, we found direct relationships between g, IQ, verbal memory and employment status in patients with schizophrenia spectrum disorders. While genetic risk for schizophrenia (PGSscz) moderated some cognitive predictors of employment outcomes, this was unexpectedly not the case for cognitive genetics (PGScog). These results suggest that therapies targeting broad cognitive ability may influence employment outcomes and that the specific domain of verbal memory might also impact real-life functional outcomes and constitute a secondary therapeutic target. Furthermore, the possibility that schizophrenia genetic risk background may play a role in moderating cognitive influences on employment status merits further investigation.

Keywords: Cognitive Impairment Associated With Schizophrenia, Functional Outcomes, Polygenetic Risk Score

Disclosure: Nothing to disclose.

P451. The Schizophrenia-Associated Variant in SLC39A8 Alters N-Glycosylation in the Mouse Brain

Robert Mealer*

Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts, United States

Background: Schizophrenia is a severe mental illness with strong heritability, and advances in genetics have started to unravel the complex molecular underpinnings of this disorder. GWAS have identified over 250 loci linked to schizophrenia, though most are in the non-coding region of the genome. The most significantly associated coding variant in schizophrenia GWAS is rs13107325 in SLC39A8, resulting in a missense mutation (A391T) in the eponymous manganese (Mn2+) transporter. Mn2+ transport by SLC39A8 is critical for glycosylation, the enzymatic attachment of carbohydrates to proteins and lipids, and we have previously shown that human carriers of A391T have reduced serum manganese, altered plasma glycosylation, and brain MRI changes consistent with altered metal transport. In this study, we employed a knock-in mouse model homozygous for A391T to investigate molecular changes in the brain resulting from the schizophrenia associated mutation, focusing specifically on the protein glycosylation pathway.

Methods: Homozygous knock-in A391T mice and controls from both sex were included in our study. Brain tissue was harvested from four regions (cortex, hippocampus, striatum, and cerebellum) at 12-weeks of age for analysis. MALDI-TOF MS glycomics of Asn (N-) and Ser/Thr (O-) linked glycans was performed on all four brain regions in groups of N ≥ 4 for both sexes, with results presented as the percent abundance of different glycan categories between regions from each genotype. Confirmatory glycan quantifications were performed using two separate techniques following derivatization using F-MAPA and sialic acid (NANA) kits. Full RNA sequencing was performed from cortex and cerebellum of A391T and control mice (N = 4/group) at the MGH NextGen Sequencing Core using standard protocols, resulting in quantification of over 14,000 transcripts from each region. Quantitative N-glycoproteomics of cortex was performed from A391T and controls (N = 5/group) following multi-lectin affinity purification, removal and tagging of N-glycopeptides using PNGase F and TMT, and analysis using a Thermo Orbitrap nano-electrospray MS.

Results: N-Glycosylation was most impaired in A391T cortex, with nearly half of the glycan categories showing significant differences (p < 0.05). Quantitative analyses confirmed a reduction of glycan concentrations in the cortex of A391T mice (Control 3.24 vs A391T 2.45 nmol N-glycans/ µg protein, p = 0.043). RNAseq analysis showed negligible variation between genotypes, consistent with changes in the activity of glycosylation enzymes rather than gene expression. Quantitative glycoproteomics showed that nearly one third of detected glycopeptides were expressed at different levels in the cortex, including members of several pathways previously implicated in schizophrenia such as cell adhesion molecules and neurotransmitter receptors. Single cell expression data of transcripts from the altered glycopeptides suggests that the proteins originate from multiple cell types across the cortex.

Conclusions: The A391T mutation associated with increased risk for schizophrenia causes small but significant changes in protein N-glycosylation in the mouse cortex, consistent with the predicted effect size of a common variant. These findings provide a mechanistic link between a risk allele and potentially reversible biochemical changes in the brain, furthering our molecular understanding of the pathophysiology of schizophrenia and representing a novel opportunity for therapeutic development targeting the glycosylation pathway.

Keywords: Glycosylation, Schizophrenia (SCZ), SLC39A8

Disclosure: Nothing to disclose.

P453. Adiposity in Schizophrenia: A Systematic Review and Meta-Analysis

Sri Mahavir Agarwal*, Emily Smith, Raghunath Singh, Jiwon Lee, Laura Colucci, Ariel Graff-Guerrero, Gary Remington, Margaret Hahn

Centre for Addiction and Mental Health, Toronto, Canada

Background: Although a relationship between schizophrenia (SCZ), antipsychotic (AP) medication, and metabolic dysregulation is now well established, the effect of adiposity is less well understood. By synthesizing findings from imaging techniques that measure adiposity, our systematic review and meta-analysis (PROSPERO CRD42020192977) aims to determine the adiposity-related effects of illness and treatment in this patient population.

Methods: We searched MEDLINE, EMBASE, PsychINFO and Scopus for all relevant case-control and prospective longitudinal studies from inception until February 2021. Measures of adiposity including percent body fat (%BF), subcutaneous adipose tissue (SAT), and visceral adipose tissue (VAT) were analyzed as primary outcomes.

Results: Our search identified 29 articles that used imaging methods to quantify adiposity among patients with SCZ spectrum disorders. Analyses revealed that patients have greater %BF (mean difference (MD) = 3.09%; 95%CI: 0.75 to 5.44), SAT (MD = 24.29 cm^2; 95%CI: 2.97 to 45.61) and VAT (MD = 33.73 cm^2, 95%CI: 4.19 to 63.27) compared to healthy controls. AP treatment was found to increase SAT (MD = 31.98 cm^2; 95%CI: 11.33 to 52.64) and VAT (MD = 16.30 cm^2; 95%CI: 8.17 to 24.44) with no effect on %BF. However, change in %BF was higher for AP-free/AP-naïve patients compared to treated patients.

Conclusions: Our findings indicate that patients with SCZ spectrum disorders have greater adiposity than healthy controls which is increased by AP treatment. Young, AP-naïve patients may be particularly susceptible to this effect. Future studies should explore the effect of specific APs on adiposity and its relation to overall metabolic health.

Keywords: Schizophrenia Spectrum Disorders, Adiposity, Antipsychotic Agents, Subcutaneous Fat, Visceral Fat

Disclosure: Nothing to disclose.

P454. A Pilot Study of Brain Activity Associated With the Rubber Hand Illusion in Youth With Schizophrenia Spectrum Disorders

Rhoshel Lenroot*, Grace Mayer, Juan Bustillo, Julia Stephen

University of New Mexico Health Science Center, Albuquerque, New Mexico, United States

Background: Self-disturbance, referring to subjective alterations in the sense of ownership of one’s body, thoughts, and actions, along with deficits in self-monitoring, is hypothesized to be a core disturbance in schizophrenia [1]. It is notable for being present during the early stages of the disorder and may be associated with increased risk for non-affective psychosis [2]. The neurophysiologic mechanisms underlying self-disturbance are not yet well understood. The rubber hand illusion (RHI) experiment has been used extensively in studies of visuo-tactile integration in the multisensory literature, and more recently to examine the sense of body ownership (feeling that one’s own body belongs to oneself). Susceptibility to the RHI has been associated with impaired body ownership mechanisms in patients with schizophrenia relative to controls, but there is very little data regarding brain activity during the RHI in individuals with schizophrenia spectrum disorders (SSD), and none in early psychosis. We therefore carried out a pilot study to examine pathophysiology underlying self-disturbance in schizophrenia by using magnetoencephalography (MEG) to compare brain activity in youth with SSD compared to healthy controls during the experience of self-disturbance induced by the RHI.

Methods: Participants included youth aged 14-25 with SSD with symptom onset within the past 5 years and age matched HC. The RHI task included three conditions in randomized order, each occurring for one 3.5minute block, based on protocol of Rao and Keyser [3]. In the first condition (Illusion), meant to induce the RHI, the left hand was placed in a box on the table in front of the subject with a tactile stimulus attached to the left index finger. A rubber hand was placed next to the box in view of the subject with an identical tactile stimulus device and a red LED which blinked synchronously with the tactile stimulus. The tactile stimulus was presented using a weak 0.5ms duration electrical current to the left index finger. In the Incongruent control condition, the rubber hand was placed in an unnatural position relative to the body such that the hand could not be mistaken for the participants own hand. In the “Real” control condition a rubber hand was not used; the left hand instead was visible while receiving tactile stimulation. The time of the onset and end points of the illusion was recorded by the participant through a button press by the right hand. The Rubber Hand Illusion Post-task Questionnaire [3] was used to measure the subjective strength of the illusion after each condition. MEG data was obtained using a 306-channel Neuromag Vector View system using standard procedures for head localization, eye blink and heart beat artifacts. Structural MRI data for co-registration with MEG was obtained using an MPRAGE sequence (1x1x1mm resolution, TR/TE/FA 2500/2.8/8; Parallel imaging 2x, 176 slices, FOV 256x256). Spectral data was processed and source localized similar to Stone et al. [4]. Participants first underwent the RHI task outside of the scanner for training and to screen for susceptibility to the RHI; HC who did not experience the illusion did not have neuroimaging. Analysis: We first compared average power during each condition (Illusion, Incongruent, Real) between SSD and HC. We then measured the difference in average spectral power between the epochs in which a participant reported experiencing the RHI and control conditions and compared these differences between groups. We focused on alpha and beta bands in right and left frontal (RF, LF) and central (RC, LC) regions, based on the findings reported by Rao and Keyser.

Results: The final sample included 14 SSD (12m, 21.6 ± 4.5yrs) and 11 HC (3m, 24.3 ± 5.4yrs). We did not find significant effects of condition (Illusion, Incongruent, Real) between groups. However, we found significant effects of diagnosis on the magnitude of the difference in spectral power between Illusion and control conditions: HC had significantly greater differences in alpha-band power between Illusion and Incongruent conditions than SSD in LF (SSD = -.089, HC = .07, p < .0001) and LC (SSD = -.068, HC = .005,p < .046), and beta-band power in LC (SSD = -.003, HC = .011, p < .013). For HC power was greater in the Illusion than in Incongruent condition, while for SSD power was slightly less in the Incongruent than Control conditions. There were not group effects in the Illusion-Real condition. The participant ratings of subjective strength of the RHI were not different between groups.

Conclusions: While self-disturbance may be a key early feature in the development of schizophrenia spectrum disorders, there is little known about associated differences in brain function. We studied youth with early psychosis, and found that while HC had significant differences in brain activity during the RHI, individuals with SSD did not, despite similar subjective reports of the strength of the illusion. While this is the first MEG study of the RHI in early psychosis, our results appear consistent with a previous EEG study in chronic schizophrenia[5] Limitations include the small sample size and lack of objective measurements of strength of the RHI. Future directions include replication in a larger sample, and relationship of findings to clinical characteristics.

References: 1. Schiz Res 152(1):1-4,2014. 2. Schiz Bull 38(6):1277-87,2012. 3. Fr Hum Neuro 11:377, 2017. 4. Acta Psychol 142(2):177-83,2013. 4. Fr Hum Neuro 8:788, 2006. 5. Schiz Res 64(2-3):157-63,2003.

Keywords: Early Psychosis, Magnetoencephalography, Rubber Hand Illusion

Disclosure: Nothing to disclose.

P455. Optimizing Cognitive Control Activity in Med-Naïve First Episode Psychosis Patients and Healthy Controls

Anita Barber*, Juan Gallego, Pamela DeRosse, Michael Birnbaum, Todd Lencz, Ashley Moyett, Anil Malhotra

Feinstein Institute for Medical Research, Glen Oaks, New York, United States

Background: Cognitive impairment is a core feature of First Episode Psychosis (FEP). While cognitive control paradigms commonly identify dysfunction in several brain circuits, they fail to identify known sources of trial-to-trial variability in cognitive control. Trial Specific Costs (TSCs) include Block Restart (BR), Previous Trial Interference (PTI), Response Switching (RS), and Stimulus Item (SI) effects, each of which elicit robust behavioral costs. The current study examined whether modeling TSCs improves detection of brain dysfunction in FEP.

Methods: 22 FEP patients (50% male, age = 24.2 (4.4) years) and 22 healthy controls (46% male, age = 27.9 (4.6) years) were scanned on a Siemens 3T Magnetom Prisma scanner with a 64-channel head/neck receiver coil. This included a T1-weighted scan (TR = 2400 msec, TE = 2.22 msec, voxel size = 0.8 mm3, scan length = 6 min, 38 sec) and four Simultaneous Multi-Slice Echo Planar Imaging scans (multiband acceleration factor = 8, TR = 720 msec, TE = 33.00 msec, voxel size = 2.2x2.2x2.0 mm) in which the Multi-Source Interference Task (MSIT) was performed. Two runs were composed of mostly congruent (75% congruent:25% interference) trials and two runs were composed of mostly interference (25% congruent:75% interference) trials.

First-level models included regressors for congruent, interference, and error trials, in addition to TSCs. The BR regressor consisted of a separate condition for the first trial of each block. The PTI regressor was a parametric modulation regressor which indicated if the previous trial was congruent or not. The RS regressor was a parametric modulation regressor which indicated if the previous trial was a response switch. The SI regressor was a parametric modulation regressor which indicated if the current stimulus was a 1, 2, or 3. First-level models also included the cardiac-BOLD regressor, reflecting fluctuations in BOLD that track heart rate, in addition to nuisance (motion and aCompCor physiology) regressors. Group models examined interference-related (interference-congruent) activity, while controlling for group, sex, age, and Framewise Displacement. Group differences were thresholded at a voxelwise and clusterwise p = 0.05. To compare model fit, subject models with and without TSCs were compared across seven functional networks (i.e. the Yeo functional parcellation networks) for average T-values for the interference control (i.e. incongruent-congruent) contrast and model Mean Squared Error (MSE) adjusted for the number of model parameters (i.e. MSE/df).

Results: The models revealed group differences in distinct networks for interference control (interference-congruent) and for each of the TSCs. While the healthy control group had greater dorsolateral prefrontal cortex and anterior cingulate cortex activation than FEP patients during interference control, different regions were identified for PTI, BR, RS, and SI effects. Paired T-tests between models including TSCs and models including all other task and nuisance regressors, but no TSCs, revealed that mean T-values were significantly greater for interference control in the Ventral Attention (t(43) = 4.5,p = 4.9x10-5), Frontoparietal (t(43) = 3.5,p = 0.0011), Dorsal Attention (t(43) = 3.1,p = 0.0028), and Visual Networks (t(43) = 2.4,p = 0.018) for the TSC models. Model fit (MSE/df) was also improved for the TSC compared to the no TSC models across the whole brain and for all networks except the Visual Network.

Conclusions: Models of cognitive control function are improved by modeling known behavioral costs reflecting within condition trial variability. Cognitive control dysfunction in First Episode Psychosis can be better characterized by examining TSCs in addition to primary condition effects.

Keywords: First Episode Psychosis, Cognition, Functional Brain Network, Task fMRI

Disclosure: Nothing to disclose.

P456. Linking Lifetime Stress to Abnormal Functional Activation and Current Stress Processing During an Anticipated Threat Task

Mark Kvarta*, Joshua Chiappelli, Jef West, Eric Goldwaser, Heather Bruce, Peter Kochunov, Elliot Hong

University of Maryland School of Medicine, Maryland Psychiatric Research Center, Catonsville, Maryland, United States

Background: Stress across the lifetime plays a major role in increasing the incidence and severity of numerous psychiatric diseases, but exactly how stress translates into impact on brain circuitry remains an area of major interest. Brain areas responsible for the processing of and response to stress have been implicated, including limbic areas like the hippocampus which itself is sensitive to damage by stress, and the insula which is a key region in psychosis symptomatology. We hypothesized that lifetime stress-induced perturbation of stress-sensitive cortico-limbic brain areas leads to altered functional activation in response to subsequent stressful situations during adulthood, underlying an altered stress responsivity in schizophrenia spectrum disorder (SSD).

Methods: We have developed a highly translational stress induction paradigm that is human MRI compatible and ethical. The ankle shock threat task (AST) paradigm is analogous to the classic approach of inducing stress in animal studies using foot shock. For this small pilot study, we recruited fifteen individuals (11 SSD patients, 8/11 male) and 4 adult community controls (CC, 2/4 male) were included in this pilot study. Structured Clinical Interview for DSM-IV was completed to verify psychiatric diagnoses. Major early life stress was recorded using the Childhood Trauma Questionnaire, while recent stress (past 30 days) was measured with the Perceived Stress Scale. Symptoms were measured with the Peters Delusional Index. fMRI data was collected using a 3-T Siemens Prisma scanner and 64-channel coil, with an electrode attached to one ankle of each participant. A pre-determined voltage was applied for 0.1s during the task (similar to the experience of touching a surface with static electricity, using the Transcutaneous Aversive Stimulator, Coulborne Instruments). There are 3 conditions in this paradigm: (1) a shock condition in which a few random shocks are delivered while a color sign on the screen indicates shocks are possible; (2) a threat condition in which the same color is present but no shock is given; and (3) a safe condition in which no shock is given and the color indicates safety. All image preprocessing includes slice timing corrections and were volume co-registered. Images were linearly detrended, normalized into MNI standard space, and spatially smoothed (FWHM = 8mm) using SPM12. First level models were developed for each subject by entering all the volumes into a single analysis regressing the “shock”, “threat” and “safe” conditions. The contrast of interest was the threat - safe condition to study how the brain is processing the threat of the unpleasant shock but without the interference of the actual shock. Multiple regression analyses were completed in SPSS (IBM). Non-significant predictors including interaction effects were removed in step-wise fashion. All experimental protocols were approved by the University of Maryland Baltimore IRB.

Results: Nominally significant group differences were found in multiple regions from the threat - safe contrast (p < 0.05) in a previous larger sample analysis. Two regions with significant patient-control activation differences were selected from this list to examine in this smaller pilot study (n = 15) due to their roles in stress processing and symptomatology: right hippocampus and right insula. In multiple regression analysis, a significant model (F(3,12) = 7.8, p = 0.002) for right insula activation included predictor variables of CTQ, PSS and PDI. In second regression model exploring the R hippocampus activation, CTQ and PSS were predictors in a significant model for right hippocampus activation (F(3,12) = 7.5, p = 0.003).

Conclusions: In this pilot study, we observed a link from past and recent stress measures to highly stress- and disease-relevant functional brain activations using an anticipated threat task. These findings suggest that more severe early life stress as well as recent stress combine to lead to altered activations revealed during an active functional imaging task, which may in part contribute to altered stress reactivity as well as symptoms in SSD.

Keywords: Lifetime Stress, Functional Neuroimaging, Hippocampus, Insula, Schizophrenia (SCZ)

Disclosure: Nothing to disclose.

P457. Diffusion Measures of Extracellular Free Water Predict Response to Treatment in Individuals With Schizophrenia-Spectrum Disorders

Tyler Lesh*, Diana Olivan, Praveena Singh, J. Daniel Ragland, Tara Niendam, Jason Smucny, Cameron Carter

University of California, Davis, Sacramento, California, United States

Background: One of the more recent developments in the care of individuals with schizophrenia and other psychotic disorders is the introduction of coordinated specialty care (CSC). Despite the advantages of this approach, clinical outcomes continue to vary widely. Consequently, there is a need to leverage precision medicine tools to optimize treatment at the individual level and maximize the impact of CSC in these individuals. We propose that neuroimmune perturbation is a developmental factor that may represent considerable heterogeneity in clinical outcomes. Evidence has been accumulating for an immune-based component of schizophrenia based on several decades of epidemiological research showing a strong link between increased risk for psychosis and maternal infections, genetic models implicating MHC-related risk genes in increased synaptic pruning during adolescence, and post mortem studies showing altered gene expression of immune related proteins in the brain in psychotic disorders. One recently developed diffusion imaging measure, extracellular free water, is a putative marker of neuroinflammation that may offer insight into these neuroimmune processes in the brain. Free water has been shown to be reliably increased in first episode psychosis, including our own early psychosis samples. Furthermore, we have identified significant relationships between gray matter free water and BPRS scores, linking this measure to clinical state. However, in many studies of free water, there is significant overlap between groups in free water values and consequently only a subset of patients may evidence a strong immune component to their illness. This heterogeneity may partly explain why several clinical trials evaluating add-on treatment using anti-inflammatory agents have shown relatively modest benefits in relieving symptomatology, with one additional study showing no benefit. Thus, the goal of this study is to evaluate the potential of baseline extracellular free water as a predictor of treatment response over a one year period in CSC in a sample of patients with first episode schizophrenia-spectrum disorders.

Methods: A total of 46 individuals with schizophrenia-spectrum diagnoses were recruited, assessed using the SCID-IV and BPRS, and enrolled in our CSC program. Participants were re-assessed after one year and those whose BPRS score improved by twenty percent or greater were considered treatment responders, while the remainder of the group were considered non-responders. All participants underwent a diffusion MRI scan on a 3 Tesla Siemens Trio scanner in which multiple b-value shells were acquired to improve estimation of extracellular free water. Diffusion images were aligned to individual subject MPRAGE scans, and existing segmented MPRAGE masks were used to define whole-brain gray- and white-matter free water estimates. Logistic regression was implemented to test the prediction that higher free water at baseline would be associated with positive response to treatment. Pearson correlations (with follow-up nonparametric analyses for non-normal data) were computed between free water values and clinical symptomatology in SPSS.

Results: After one year in treatment, 26 individuals were classified as treatment responders and 20 as non-responders, based on the twenty percent BPRS improvement threshold. In line with our predictions, treatment responders showed a trend for higher whole-brain gray matter free water values at the baseline assessment (t = 1.91, p = .06, OR = 1.9). Additionally, higher gray matter free water values were negatively associated with BPRS scores at 12 month follow-up (r = -.384, p = .008), suggesting that those who initially presented with high free water values tended to show low symptomatology at follow-up. Whole-brain white matter free water was not significantly different between responders and non-responders (p = .73) and showed a similar but non-significant relationship to symptoms at follow-up (r = -.18, p = .23).

Conclusions: These data suggest that even with gold-standard CSC a substantial proportion of patients did not show a clinically meaningful response to treatment. However, whole-brain gray matter free water showed promise as a predictor of treatment response, given that individuals showing high free water levels at baseline were more likely to be classified as treatment responders one year later, albeit at a trend level of significance. These data were consistent with significant inverse correlations between gray matter free water and BPRS scores at one year, which suggest that those who began the study with a more prominent inflammatory profile showed lower symptoms at follow-up. These relationships were largely unique to free water present in the gray matter, showing some specificity to tissue type. While preliminary, these data suggest that the use of MRI-based markers, such as free water, may offer the potential of a more personalized approach to future clinical trials of inflammation-related therapies, in which patients are stratified based upon diffusion MRI data and offered targeted intervention based upon these measures. Finally, additional participants are being continually recruited and new participants will be added to the sample for the poster presentation.

Keywords: Free Water Imaging, Schizophrenia (SCZ), Treatment Response, Psychotic Disorders

Disclosure: Nothing to disclose.

P458. Reducing Cardiovascular Effects in Ketamine PharmacoBOLD

Jack Grinband*, Joshua Kantrowitz, Lawrence Kegeles, Daniel Javitt

Columbia University, New York, New York, United States

Background: Schizophrenia is associated with psychotic symptoms that remain partially or fully refractory to standard antipsychotic medications for ~2/3 of patients. Alternative, glutamatergic approaches for treatment development have been proposed but have not yet led to FDA-approved medications. A major barrier to effective glutamatergic treatment development is the absence of validated measures for target engagement that can identify effective compounds and guide dose selection. As part of the recently completed NIMH multicenter FAST-PS initiative, we evaluated ketamine-induced pharmacoBOLD (phBOLD) in healthy volunteers (HV) as a potential target engagement biomarker for development of metabotropic glutamate (mGluR2/3) agonists. In our initial HV study, we demonstrated that ketamine induces a robust increase (p < 0.0001, Cohen’s d = 5.4) in phBOLD response. In FAST-PS, we selected a high dose of ketamine (0.23 mg/kg) in order to produce robust pharmacological effects. However, at this dose, ketamine-induced tachycardia can influence cerebrovascular volume and oxygenation, and thus phBOLD, which may add “noise” to phBOLD comparisons. In the present study, we titrated this dose downward in HV in order to identify doses that produce reduced psychotomimetic effects, but nevertheless sufficiently robust (d = ~1.5) phBOLD effects to permit detection of mGluR2/3 agonist effect while at the same time minimizing cardiovascular effects.

Methods: HV participated in 2 identical phBOLD sessions at least 7 days apart in 10 person cohorts for a total of 20 subjects. On both days, clinical assessments were performed following removal of the subject from the scanner. The first cohort received 0.08 mg/kg, which has previously been shown to produce a large effect size (d = 1.97). The second cohort received 0.06 mg/kg. We regressed out the effects of cardiorespiratory variance and assessed the correlation between phBOLD magnitude in dorsal ACC and symptoms. This approach allowed us to identify the lowest ketamine dose at which reliable phBOLD effects are observed, in order to minimize psychotomimetic/non-specific perfusion effects in future studies.

Results: At 0.08 mg/kg ketamine, the phBOLD response peaked at ~3 min with a ~1% signal change. The peak responses during the first and second scan were not significantly different from each other (t-test, p = 0.49). A full reliability analysis will be conducted once data from all cohorts are finished being collected. The preliminary effect size for scan 1 is 3.7, which shows the expected drop off from our previous study using a 0.23 mg/kg bolus (d = 5.4). The behavioral results from the 1st and 2nd cohorts shows the expected dose response. The BPRS increase in the present study remains significant (p = 0.02, d = 0.61). No significant cardiovascular changes were seen.

Conclusions: This preliminary data confirms that phBOLD can still produce robust effects and be used for reliable testing of novel glutamatergic compounds while also avoiding the most common fMRI confound from ketamine administration. The robust phBOLD and BPRS response suggests that further downward titration is possible.

Keywords: Schizophrenia, Antipsychotics, Ketamine, PharmacoBOLD

Disclosure: Nothing to disclose.

P459. In Vivo Plasticity Between Ventral Hippocampal Inputs and Medial Prefrontal Cortex Microcircuits in a Mouse Model of 22q11.2 Deletion Syndrome

David Kupferschmidt*, Thomas Clarity, Rachel Mikofsky, Kirsten Gilchrist, Maxym Myroshnychenko, Joshua Gordon

National Institute of Neurological Disorders and Stroke (NINDS), Bethesda, Maryland, United States

Background: Functional connectivity between rodent ventral hippocampus (vHPC) and medial prefrontal cortex (mPFC) supports cognitive functions such as spatial working memory (SWM), and is disrupted in Df(16)A + /– mice with a microdeletion syntenic to the schizophrenia-predisposing 22q11.2 microdeletion. Optogenetic inhibition of direct vHPC-mPFC neural projections or somatostatin-positive (SST+) interneurons in mPFC of wildtype (WT) mice impairs vHPC-mPFC connectivity and SWM performance, mimicking the effects of the microdeletion. To examine how functional interactions between these circuit elements may contribute to vHPC-mPFC dysconnectivity in Df(16)A +/- mice, and how these interactions may be altered to promote vHPC-mPFC connectivity, we tested the ability of vHPC-mPFC inputs to modulate in vivo activity of discrete mPFC neuronal populations in WT and Df(16)A +/- mice using an all-optical approach.

Methods: The red light-activated channelrhodopsin ChrimsonR was expressed in vHPC neurons of adult male and female WT and Df(16)A +/- mice. The calcium indicator GCaMP6f was expressed in mPFC SST + interneurons, parvalbumin-positive (PV+) interneurons, and CaMKII+ pyramidal neurons in separate cohorts (n = 5-13). Red light pulses were delivered to the mPFC to excite vHPC terminals, and postsynaptic activation of GCaMP6f was simultaneously monitored using fiber photometry.

Results: Stimulation-evoked photometric responses in SST + interneurons varied systematically with pulse number (1-40) and frequency (1-40Hz), with maximal responses achieved by 40 pulses at 40Hz. SST + interneuron responses in Df(16)A +/- mice were weaker than those in WT mice (p = 0.03, main effect of Genotype, 3-way ANOVA). Repeated daily high-frequency stimulation over 12 days increased evoked SST + interneuron responses for up to 50 days in both genotypes (p = 0.006, Day x Stimulation, 3-way ANOVA). High-frequency stimulation in Df(16)A +/- mice potentiated SST + interneuron responses to levels observed in WT mice without such stimulation. PV + interneuron responses to high-frequency stimulation in WT mice were weak and biphasic; the negative component of this response was non-significantly enhanced across stimulation days (p = 0.064, one-way ANOVA). CaMKII+ pyramidal neuron responses to the same high-frequency stimulation in WT mice were unchanged across stimulation days (p = 0.235, one-way ANOVA). Behavioral tracking of all mice revealed no evidence of differences in locomotion or position within the stimulation chamber that explain the group differences or time-dependent changes in neural responses.

Conclusions: These findings suggest that the capacity of vHPC inputs to engage mPFC SST + interneurons may be impaired in Df(16)A +/- mice, and that repeated high-frequency stimulation of vHPC-mPFC inputs induces in vivo plasticity that may involve recruitment of SST + interneurons. Future work will assess how this plasticity influences SWM performance. Together, these data reveal properties of cell-type-specific functional connectivity within intact vHPC-mPFC circuits that inform how discrete circuit elements may interact to mediate normal and disordered cognitive function.

Keywords: Hippocampal-prefrontal, GABAergic Interneurons, Neural Plasticity, 22q11 Deletion Syndrome, Functional Connectivity

Disclosure: Nothing to disclose.

P460. AUT00206, a First-In-Class Kv3 Modulator, Improves Auditory Processing in Patients With Schizophrenia

Charles Large*, Victoria Sanchez, Anil Sajjala, Alice Sharman, Oliver Howes, Stephen Kaar, Daniel Umbricht

Autifony Therapeutics, Stevenage, United Kingdom

Background: Evidence suggests that patients with psychotic illness show deficits in primary auditory function [Javitt et al. 2015, Am.J.Psych 172, 17-31], including real-world difficulties, such as understanding speech in a background of noise [Illiadou et al. 2013, Am.J.Aud. 22, 201-208]. Auditory deficits likely impact social and cognitive function, and contribute to or exacerbate other symptom domains. Early treatment of sensory deficits could reduce or prevent psychotic episodes. Kv3.1 potassium channels are critical for the function of neurons in auditory circuits [Kaczmarek 2012, PLoS Comp. Biol. 8, e1002424]. Positive modulation of Kv3.1 channels can rescue deficits in auditory temporal processing in rodents [Chambers et al, 2017, Sci. Rep. 7, 17496]. AUT00206 is a novel Kv3.1 modulator that reduced the impact of ketamine on BOLD responses in healthy volunteers [Deakin et al. 2019, Schiz. Bull. 45, S245-S246]. Here, we investigated the ability of AUT00206 to improve auditory function in patients with schizophrenia.

Methods: In a randomised, double-blind, placebo-controlled study, 24 subjects with schizophrenia (< 5 yrs since diagnosis) were randomised 2:1 to AUT00206 or placebo for 28 days (NCT03164876). Clinical and exploratory biomarker assessments were completed by all subjects. Audiological assessments were completed by 11 subjects on AUT00206 and 4 on placebo. At Baseline, Day 1, and three days over a 28-day period, subjects completed a comprehensive test battery that probed different levels of auditory information processing including otoacoustic emissions (OAEs), pure-tone audiometry, mismatch negativity (MMN), and a Words-in-Noise test (WIN).

Results: All patients had clinically normal hearing thresholds and performed within normal ranges on tests of basic auditory function. Tests that indicated abnormal auditory processing at baseline (MMN, WIN), showed an improvement with treatment. A consistent increase in OAEs and contralateral suppression of OAEs was observed in the AUT00206 group that reached statistical significance at several frequencies. Increased amplitude of pitch MMN was observed over the course of the dosing period in the AUT00206 group compared to baseline and placebo. Performance of the WIN test at 40dB HL showed a significant treatment difference between AUT00206 (-2.6dB improvement) and placebo (+0.8dB worsening) (p = 0.016). Seventy percent (7/10) of the AUT00206 subjects showed an improvement in WIN performance by Day 21, with only twenty five percent (1/4) showing an improvement on placebo. The degree of improvement in OAEs and WIN performance in AUT00206 group at Day 21 is considered highly clinically relevant.

Conclusions: Treatment with AUT00206 improved measures of auditory information processing at different levels of the auditory system in patients with schizophrenia, consistent with a critical role for Kv3.1 channels in high fidelity information processing and transfer. Treatment with Kv3.1 modulators may not only correct information processing at higher cortical levels, but also ameliorate sensory deficits across all modalities – a novel, but long overdue approach that may help improve symptoms and quality of life through a bottom-up effect in patients with schizophrenia. These results provide the first evidence that targeting PV + interneuron through modulation of their intrinsic ion channels is an important new approach to the treatment of information processing disorders, such as schizophrenia. Future studies will have to establish if Kv3.1 modulators also improve other dysfunctions such as cognitive deficits believed to be due to PV + interneuron dysfunction.

Keywords: Kv3 Channels, Parvalbumin Neurons, Auditory Processing, Schizophrenia

Disclosure: Autifony Therapeutics Limited: Stock / Equity, Board Member, Employee (Self)

P461. Acetylated Chromatin Domains Link Chromosomal Organization to Cell and Circuit Level Dysfunction in Schizophrenia

Kiran Girdhar*, Gabriel Hoffman, Jaroslav Bendl, Samir Rahman, Pengfei Dong, Will Lao, Leanne Brown, Olivia Devillers, Bibi Kassim, Jennifer Wiseman, Royce Park, Elizabeth Zharovsky, Rivky Jacobov, Elie Flatow, Yan Jiang, Alexej Kozlenkov, Stella Dracheva, Mette Peters, Marija Kundakovic, Stefano Marenco, John Fullard, Schahram Akbarian, Panos Roussos

Icahn School of Medicine at Mount Sinai, New York, New York, United States

Background: The three-dimensional (3D) genome organization is crucial for the interplay between cell specific gene expression, chromatin structure, and other factors (e.g., histone modification) underneath our brain functions. Dysregulation of transcription and chromatin structure leads to debilitating disorders such as autism and schizophrenia (SCZ). To explore the dysregulation in chromatin structure in SCZ and bipolar disorder (BD), we capitalized on histone modification landscapes as they are tightly linked to chromatin structures.

Methods: In the first part of the study, we mapped active promoter- and enhancer-associated histone methylation (H3K4me3) and acetylation (H3K27ac) profiles in PFC of 564 brain donors, providing to date the largest histone modification dataset for SCZ and BD.

In the second part of this study, we built chromatin structure by leveraging the inter-individual correlations between histone peaks to identify domains of physically interacting regulatory elements called cis-regulatory domains (CRDs). Our in-silico biological validation of CRDs from both assays H3K4me3 and H3K27ac showed tight link to the structures of self-interacting domains, with enrichments of CTCF structural proteins at CRD domain boundaries, which is in line with CTCF enrichment of PFC NeuN+ Hi-C defined TAD boundaries.

Results: Dysregulation of enhancer-associated histone modified peaks (H3K27ac) across SCZ (BD) cases and controls showed stronger enrichment of SCZ (BD) GWAS risk variants in neurons than in tissue. Additionally, we noticed enrichment in SCZ variants was coming from hyper-acetylated peaks but not from hypo-acetylated peaks.

Next, we investigated dysregulation in chromatin structure using CRDs expression as a metric. Interestingly, SCZ and BD sensitive CRDs which were hyper-acetylated were strongly enriched for SCZ (BD) GWAS risk variants than hypo-acetylated CRDs. To further explore the role of disease sensitive CRDs, we created another layer of chromatin by taking the inter-individual correlation of diseased CRDs which manifested A/B compartments of chromatin organization. K-means clustering of correlation of disease-sensitive H3K27ac CRDs revealed strong, cluster-specific convergences defined by A/B compartment chromatin organization, dysregulation (hypo vs. hyper-acetylation), cell types and specificity towards neurodevelopment. Cluster with majority of hyper-acetylated CRDs were strongly enriched for glutamatergic specific H3K27ac peaks and chromHMM active chromatin states in fetal brain linking the connection of SCZ and BD with neurodevelopment.

Finally, the projection of hyper-acetylated CRDs from A-compartment cluster in three-dimensional genome constructed using chrom3D utilizing PFC-NeuN+ HiC showed localization of disease sensitive TADs in 3D nuclear 3D space linking neuronal 3D genome, or chromosomal organization in psychiatric disorders.

Conclusions: We showed that hyperacetylated CRDs were strongly enriched for excitatory projection neuron-specific peaks with regulatory sequences indexed by chromHMM as active chromatin showing significant associations with SCZ and BD genetic risk architectures for the adult, and in case of SCZ, also the fetal PFC. Therefore, this cluster-specific fingerprint could signal that many chromatin domains important for PFC projection neurons play a critical role early in the disease process.

Taken together with the finding that chromatin states of the fetal brain are disproportionally over-represented among the set of common risk variants linked to schizophrenia, a finding that was replicated for the group of hyperacetylated enhancers in SCZ groups, it is plausible to hypothesize that a subset of hyperacetylated chromatin domains in diseased PFC neurons are vestiges of an early occurring neurodevelopmental disease process.

In summary, the work presented here describes some of the first fine-mappings of chromosomal domains in large series of disease and control brains, primarily defined by the correlational structure of nucleosomal histone modifications and then integrated into the Hi-C chromosomal conformation landscape. We expect that the findings and resources presented here, which were highly reproducible across various brain collections, will provide a unique roadmap for future studies aimed at gaining a deeper understanding of this emerging link between the neuronal 3D genome, or chromosomal organization, and cell-circuit-specific neuronal dysfunction in psychosis including underlying genetic risk architectures.

Keywords: Neuropsychiatric Disorders [Schizophrenia, Parkinson’s Disease, Major Depressive Disorder], Computational Methods, Histone Acetylation, Histone Methylation

Disclosure: Nothing to disclose.

P462. Pre-Clinical Evaluation of Hippocampal Long-Term Potentiation After Acute and Sub-Chronic Oral Dosing With Luvadaxistat in Mice

Jordi Serrats*, Rosa Fradley, Venkatesha Murthy, Patricio O’Donnell, Mahnaz Asgharnejad

Engrail Therapeutics, San Diego, California, United States

Background: Luvadaxistat (also known as TAK-831, NBI-1065844) is a highly selective and potent inhibitor of the D-amino acid oxidase (DAAO) enzyme (Howley et al., 2017) being studied in the clinic for cognitive impairment associated with schizophrenia (CIAS). Inhibition of DAAO results in an increase in D-serine, a co-ago¬nist of the NMDA receptor (Hondo et al., 2013; Howley et al., 2017). Luvadaxistat has been studied pre-clinically in a variety of assays relevant to assess cognitive performance in rodents (i.e., novel object recognition task, attention set-shifting task, and eye-blink conditioning). Notably, a sensitization in the behavioral response in novel object recognition task (a decrease in the minimum effective dose with a loss of efficacy at higher doses) was demonstrated after sub-chronic dosing of luvadaxistat (14 d) when compared to responses after acute dosing (Fradley et al., in preparation). The observation of sensitization suggested that luvadaxistat may be influencing hippocampal synaptic plasticity after sub-chronic dosing. We studied hippocampal synaptic plasticity using a well-established long-term potentiation (LTP) paradigm after acute and sub-chronic (14 d) dosing with luvadaxistat.

Methods: Mice (total of 97; n = 5–8 per condition) were given an acute or chronic dose of luvadaxistat (from 0.001 mg/kg to 10 mg/kg, p.o.) and hippocampal slices were harvested after 5 hours. Cerebellum and blood plasma were also obtained to measure D-serine levels achieved in the experimental animals. Electrophysiological recordings were obtained from a single slice placed on the chamber and perfused with aCSF at a constant rate. Extracellular fEPSPs were recorded in the CA1 stratum radiatum using a glass micropipette filled with aCSF. fEPSPs were evoked by electrical stimulation of Schaffer collaterals/commissural pathway at 0.1 Hz with a glass stimulating electrode placed in the stratum radiatum. To test the effect of luvadaxistat on basal synaptic transmission, Input/Output (I/V) curves were constructed at the beginning of the experiment. The slope of fEPSPs was measured and plotted against different intensities of stimulation (from 0 to 100 uA). Long-term potentiation was induced by a theta burst stimulation protocol (10 bursts of 4 pulses at 100 Hz, 200 ms between bursts) at baseline stimulation intensity. Following this conditioning stimulus, a 1 hr test period was recorded where responses were again elicited by a single stimulation every 10 s (0.1 Hz) at the same stimulus intensity

Results: Luvadaxistat produced a dose-dependent increase in D-serine levels in mouse brain (from 8.7 nmol/g to 34 nmol/g) and mouse plasma (from 213 ng/ml to 490 ng/ml). Acute dosing of luvadaxistat did not induce a measurable change in LTP. However, when luvadaxistat was dosed sub-chronically (14 d), there was a statistically significant increase (1-way ANOVA post-hoc multiple comparison analysis) in LTP after 0.001 mg/kg (*, p < 0.05 vs vehicle) and 0.01 mg/kg dose (**, p < 0.01 vs vehicle). Higher doses (0.1 mg/kg and 10 mg/kg) induced decreases in LTP.

Conclusions: Luvadaxistat induced dose-dependent increases in plasma and brain D-serine as demonstrated previously (Howley et al. 2017). Sub-chronic dosing with luvadaxistat significantly increased LTP suggesting increases in synaptic plasticity. Higher doses (0.1 to 10 mg/kg) decreased LTP, suggesting an inverted U-shape dose response. This phenomenon may underlie the leftward shift in behavioral responses (i.e., novel object recognition task) observed after acute vs chronic dosing (Fradley et al., in preparation). The leftward shift of the dose-response relationship reported in this study may suggest low doses may be efficacious in clinical trials of DAAO inhibitors.

Keywords: Long Term Potentiation, Synaptic Plasticity, D-serine, Cognitive Impairment Associated with Schizophrenia, D-Amino Acid Oxidase

Disclosure: Engrail Therapeutics: Employee (Self)

P463. Context-Dependent Effects of Haloperidol on Rat Brain Volumes and Structural Covariance Networks: An Ex Vivo MRI Study in a Rat Maternal Immune Activation Model

Chloe Walsh, Zsuzsa Lindenmaier, Marie-Caroline Cotel, Ewelina Lenartowicz, Sridhar Natesan, Jason Lerch, Anthony Vernon*

Institute of Psychiatry, King’s College London, London, United Kingdom

Background: Apparent changes in regional brain volumes and structural covariance are commonly reported in Magnetic Resonance Imaging (MRI) studies of individuals with schizophrenia (SZ). An unresolved question however is whether these apparent changes are driven by the underlying illness or represent iatrogenic effects of antipsychotic medication. We previously reported that that chronic exposure to haloperidol or olanzapine decreased rat whole brain and cortical volume (Vernon et al. Biol. Psych. 2014). A limitation of this work however is the use of naïve animals, which lack any pathology relevant to SZ. To address this, we investigated the impact of adult haloperidol (HAL) exposure on rat brain volumes and networks of structural covariance in a maternal immune activation (MIA) model of relevance for SZ, using high resolution ex vivo structural MRI. We hypothesised HAL will induce differential (i.e context-dependent) changes in these measures in MIA-exposed offspring as compared to controls.

Methods: Male Sprague-Dawley rat offspring from control (CON; saline, i.v.; GD15; n = 5 dams) and MIA exposed dams (POL; poly I:C, 4 mg/kg i.v. GD15; n = 5 dams) were randomly allocated to one of four groups: CON/vehicle; CON/haloperidol; POL/vehicle and POL/haloperidol, comprising n = 10 offspring per group. Each group contained a maximum of n = 2 offspring from the same litter. Vehicle (VEH) or the D2-receptor antagonist haloperidol (HAL; 0.5 mg/kg/d s.c.) were administered for 28 days via osmotic mini-pumps in adulthood starting on postnatal day (P)80. At the end of treatment (P108) rats were culled and perfused with 4% PFA, with the brain left in the cranium. T2-weighted ex vivo 3D MR images were acquired using a 7T small bore MRI scanner (Agilent technologies) and a quadrature volume radiofrequency (RF) coil (39 mm inner diameter, RAPID Biomedical) using the following parameters: TE/TR = 60/2000, echo train length = 8, matrix size = 192x128x192 and field of view (FOV) = 28.8x19.2x28.8 mm, yielding isotropic voxels of 150 µm3. Total scan-time per brain was 1hr 44min. MR images were converted to NIFTI format and processed using a combination of FSL, ANTs and in-house Python software. Regional brain volumes were extracted following registration to a publicly available rat brain MRI atlas (Papp et al. Neuroimage, 2014). Group differences were assessed for each atlas brain region of interest (ROI; n = 61) using linear models with between-group effects of “prenatal treatment” (CON or POL) and within-group effects of “postnatal treatment” (VEH or HAL), and their interaction, including total brain volume as a covariate. Multiple comparisons were controlled for using the False Discovery Rate (5%). To assess structural covariance by region within the dataset, the volumes of n = 44 atlas-segmented grey matter brain ROIs were subjected to correlational analysis using Pearson’s r as the readout. Correlational data were grouped into five anatomical clusters defined by agglomerative hierarchical clustering. Mean r-values for each group correlation matrix were compared using a Kruskal-Wallis 1-way ANOVA. All statistical analysis used custom scripts written in R-studio (version 1.4.1106).

Results: Statistically significant effects of prenatal treatment (CON vs. POL) were found for 5% (3/61) of rat brain atlas ROIs. Specifically, substantia nigra volumes were decreased, whilst the volumes of the cingulate and frontal association cortex were increased (all ηp2 > 0.35). There were no statistically significant effects of postnatal haloperidol (VEH vs. HAL) exposure. Consistent with context-dependent drug effects, statistically significant interaction effects (prenatal * postnatal treatment) were however found for 7% (4/61) of rat brain atlas ROIs. These included the inferior colliculus, fornix, bed nucleus of the stria terminalis (BNST) and white matter tracts (all ηp2 > 0.25). Illustrating these data, BNST volumes were reduced in POL/VEH rats, relative to all other treatment groups. By contrast, there were no differences between POL/HAL rats and CON/VEH or CON/HAL rats, suggestive of a normalising effect of HAL exposure in POL offspring on the volume of the BNST. Mean r-values derived from structural covariance matrices were significantly different across the groups (Kruskal-Wallis p < 0.01; eta2 [H] > 0.1), with increased overall structural covariance in POL/VEH rats relative to all other groups (Bonferroni post-hoc p < 0.05). Visual inspection of cluster-level changes in POL/VEH rats suggests this is driven by increased structural covariance between brainstem, hippocampal and frontal cortical ROIs. These effects were not observed in POL/HAL rats, which no longer differed from CON/VEH or CON/HAL rats, suggestive of a normalising effect.

Conclusions: We found that prenatal POL exposure leads to regional brain volume and structural covariance changes in the adult rat brain, consistent with our prior work (Crum et al. Brain Behaviour and Immunity, 2017). Furthermore, we provide preliminary evidence that adult HAL exposure has context-dependent effects on regional brain volumes and structural covariance networks in the rat brain. In particular, HAL exposure appeared to normalise putative pathological changes observed in the POL-exposed rats. Longitudinal in vivo MRI studies and behavioural assessment in offspring of both sexes are now required to confirm these data and establish the underlying cellular correlates.

Keywords: Antipsychotic, Schizophrenia (SCZ), Animal Models, Maternal Immune Activation

Disclosure: Nothing to disclose.

P464. Long-Range Synchronization in the Alpha-Band Differentially Engages VIP and SST Interneurons in Visual Cortex to Support Novelty Detection During an Oddball Paradigm

Georgia Bastos, Jacob Holmes, Anna Radar, Jordan Hamm*

Georgia State University, Atlanta, Georgia, United States

Background: People with schizophrenia exhibit difficulties in the processing of basic sensory information in a broader spatiotemporal and behavioral context. Such abnormalities undermine how affected individuals perceive and cognitively relate to their world. Impaired sensory context processing is reflected in reduced early cortical registration of contextually novel stimuli, as recorded with EEG and indexed via the “mismatch negativity” biomarker during visual or auditory “oddball” paradigms. Despite this observation, the basic cellular and circuit basis of mismatch negativity and underlying contextual processing functions remain unclear, both in terms of basic neurobiology and as it relates to pathology. We recently translated a classic visual oddball paradigm to mice to understand the basic neural mechanisms of how preceding context modulates neural processing of incident stimuli. This work identified large neural responses to rare stimuli in the “oddball” paradigm (i.e. “deviance detection”, a neural correlate of mismatch negativity) that were localized to superficial layers of primary visual cortex (V1). Optogenetically suppressing distal inputs to V1 from prefrontal cortex (ACa) eliminated this effect. Here we sought to understand how these top-down inputs interact with superficial layers of V1 at the circuit level, and how this relates to neuro-oscillatory signatures of mismatch negativity commonly measured in clinical settings.

Methods: We recorded electrophysiological and calcium signals in awake head-fixed mice (male and female; VGlut-cre, VIP-cre, SST-cre) during classic visual oddball and “many-standards control” sequences, which allowed the separation of genuine deviance detection signals to novel stimuli from the simple absence of stimulus specific adaptation. Local field potentials (LFPs) were recorded with bipolar electrodes placed in V1 and ACa (n = 7 mice). Two-photon calcium imaging of vasoactive intestinal peptide positive interneurons (VIP), somatostatin postive interneurons (SSTs), and pyramidal neurons (PYRs) from layers 1-4 of V1 were recorded while prefrontal inputs to V1 were ontogenetically driven at paradigm-relevant frequencies (ChR2; 2 to 40-Hz; n = 6 mice). Finally, chemicogenetic silencing of VIP interneurons (DREADDs; hM4Di vs CNO-only controls) was carried out during LFP recordings to determine their relevance as a local mediator of ACa-V1 synchrony and “deviance detection” signals (n = 14 mice).

Results: During the oddball paradigm, ACa and V1 displayed strong phase-locking (Rayleigh statistic>0.4; p < .001) at theta to alpha frequencies (6-10hz). Rhythmically activating ACa axons in V1 in this frequency range (but not e.g. gamma or delta) activated both VIPs and PYRs but suppressed SSTs in V1 (rmANOVA for each cell type). Chemicogenetically suppressing V1 VIP cells during the oddball paradigm selectively eliminated ACa-V1 coherence in the 6-10-Hz range (d = 0.92; hM4Di mice) and disrupted V1 deviance detection signals in the 1-10Hz LFP signal (d = 0.41; hM4Di mice; mixed-ANOVA with hM4Di n = 6 mice vs CNO-only controls (n = 8 mice); pre-vs-post CNO).

Conclusions: Our results suggest that top-down inputs to V1 engage a canonical VIP to SST inhibitory motif in V1, specifically in the theta-alpha band. This VIP-SST motif may effectively disinhibit local sup-populations of PYR neurons in V1, giving rise to augmented “deviance detection” signals (i.e. the neurobiological basis of mismatch negativity) to rare stimuli in the oddball paradigm.

Keywords: Visual Cortex, Mismatch Negativity, GABAergic Interneurons, Neuronal Oscillations, Prefrontal Cortex

Disclosure: Nothing to disclose.

P465. Automated Language Analysis of Emotional Expression in Schizophrenia: Development of a Novel Method and Preliminary Findings

Ellen Bradley*, Jake Portanova, Benjamin Buck, Josh Woolley*, Trevor Cohen*

University of California San Francisco, San Francisco, California, United States

Background: Social cognitive deficits associated with schizophrenia are core features of the illness and strong predictors of functional outcomes. A major barrier to targeting these deficits is quantifying them effectively and efficiently. Standard social cognition assessments often rely on subjective judgements, have limited resolution, and are expensive to administer. Recent studies examining these assessments have demonstrated that most widely used measures have suboptimal psychometric characteristics. There is a critical need for objective, precise, and low-cost measurement approaches for application in research and clinical care. Recent advances in computational methods from artificial intelligence and natural language processing (NLP) have transformed our ability to gain clinical insights from speech, a rich source of data, and several studies have examined their application in schizophrenia. Thus far, however, NLP tools have mostly been used to examine semantic coherence as an indicator of thought disorganization. Whether similar automated methods can be used to estimate social cognitive function in schizophrenia is unclear. In this study, we aimed to address this gap by developing a novel method of quantifying free responses to naturalistic, accessible, emotionally evocative content and tested this approach in a pilot sample.

Methods: As part of a clinical trial, 39 men with schizophrenia and 51 neurotypical control men completed an experimental task during which they viewed a series of brief, emotionally evocative video stimuli that are publicly available. After viewing each stimulus, participants had 30 seconds to respond verbally to an on-screen prompt: “How did the video make you feel?” We audio recorded and transcribed these responses. Then we used a neural network trained to identify expression of emotion in text to derive a measure of each participant’s emotional alignment relative to average neurotypical responses. For each transcript, the neural network provided a probabilistic estimate for expression of 27 distinct emotions--a vector of emotion probabilities. The emotional alignment score (ranging from 0-1) reflects the cosine similarity between this emotion vector and the average vector computed from the neurotypical sample. We also computed an emotional alignment score for each neurotypical control participant using leave-one-out cross-validation (i.e., comparing to the average vector from every other control). To assess the specific contribution of our emotion alignment metric, we computed sentence-level coherence--a common metric used in language analysis in schizophrenia--and compared relationships to clinical characteristics between both metrics: coherence and emotional alignment.

Results: We found that patients showed impaired emotional alignment (M = 0.447, SD = 0.148) relative to controls (M = 0.534, SD = 0.139), t(72.644) = 2.770, p = 0.007. Better emotional alignment was associated with better performance on a mentalizing task, r(80) = 0.328, p = 0.003; less severe negative symptoms, r(82) = -0.364, p = 0.001; and a higher level of functioning, r(82) = 0.319, p = 0.003. It was not associated with positive symptom severity, r(34) = 0.093, p = 0.590. Coherence was also impaired among patients (M = 0.797, SD = 0.060) relative to controls (M = 0.825, SD = 0.053), t(69.835) = 2.299, p = 0.024. However, coherence was not associated with negative symptoms, r(82) = -0.053, p = 0.633; level of functioning, r(82) = 0.131,p = 0.235; mentalizing performance, r(80) = 0.128, p = 0.251; or positive symptom severity, r(34) = 0.159, p = 0.354. Comparing each metric’s ability to classify participants (patient vs. control), we found that emotional alignment performed slightly better than coherence (AUROC of 0.675 vs. 0.625), and that combining the two resulted in improved performance (AUROC of 0.700).

Conclusions: An automatically computed measure of emotional alignment may provide an easily obtained estimate of social cognitive function in schizophrenia that complements existing NLP metrics used for clinical assessment of other symptom domains. Additional work is needed to validate this approach and to replicate our preliminary findings in larger and more diverse samples.

Keywords: Schizophrenia (SCZ), Natural Language Processing (NLP), Emotion

Disclosure: Nothing to disclose.

P466. RNA Editing in the Hippocampus Mitigates Behavioral Deficits Associated With Prenatal Stress

Greg Bristow, Tristram Buck, Monsheel Sodhi*

Loyola University Chicago Stritch School of Medicine, Maywood, Illinois, United States

Background: Psychological stress during pregnancy has been linked with developmental delay in addition to increased risk for disorders associated with impaired socialization in male offspring but not in females (Hodes and Epperson 2019). An epitranscriptomic process known as RNA editing plays an important role in brain development (Hwang, Park et al. 2016) and altered levels of RNA editing have been detected in the hippocampus of individuals with neurodevelopmental disorders (Tran, Jun et al. 2019).

Methods: In this study, we exposed pregnant mice to prenatal restraint stress three times daily during weeks 2 and 3 of gestation. Male offspring that were exposed to prenatal stress (n = 20) and a group of male controls (n = 20) received treatment with haloperidol (1mg/kg), clozapine (5mg/kg) or saline twice daily for 5 days in adulthood before we measured social behavior using the three-chamber test for social interaction, and locomotor activity. After euthanasia, we used quantitative PCR and/ or next-generation sequencing to measure RNA editing in the prefrontal cortex and hippocampus of the mice. We also tested female mice (n = 20) for social behavior and locomotor activity after exposure to prenatal stress. This sample size of 20 mice provides 80% power to detect a linear relationship between social interaction and the abundance of an RNA editing isoform with an R square value of 0.3 and probability level = 0.05.

Results: Prenatally stressed male mice had lower social interaction relative to non-stressed male mice (F = 17.0, df = 1, 18, p = 0.001). Prenatally stressed mice treated with clozapine had higher social interaction levels than the prenatally stressed group treated with vehicle (F = 11.5, df = 1,18, p = 0.009). Social interaction behavior correlated with hippocampal RNA editing of: α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits GluA2 (R = 0.57, F = 8.80, df = 1, 18, p = 0.008), GluA3 (R = 0.49, F = 5.59, df = 1, 18, p = 0.030) and GluA4 (R = 0.48, F = 5.43, df = 1, 18, p = 0.032), the potassium channel Kv1.1 (R = 0.766, F = 25.5, df = 1, 18, p < 0.0001), the calcium channel subunit Cav1.3 (R = 0.49, F = 5.70, df = 1, 18, p = 0.028), calcium-dependent secretion activator (CAPS-1) (R = -0.45, F = 4.62, df = 1,18, p = 0.046) and the calcium-dependent cell adhesion protein, cadherin 22 (CDH22) (R = 0.51, F = 6.22, df = 1, 18, p = 0.023). Treatment with clozapine, but not haloperidol, reversed the deficits in social interaction and GluA2 RNA editing in prenatally stressed mice (F = 26.3, df = 1, 8, p = 0.001). GluA2 RNA editing was not altered in the prefrontal cortex of prenatally stressed mice. We did not observe these effects in female mice.

Conclusions: Reduced RNA editing of molecules regulating calcium homeostasis may contribute to impaired hippocampal function after exposure to prenatal stress in male mice. Clozapine may improve social interaction through an indirect mechanism that includes the upregulation of GluA2 RNA editing in the hippocampus but not the prefrontal cortex. These data indicate that prenatal stress modifies an epitranscriptomic pathway leading to lifelong deficits in social behavior. These findings may lead to the development of therapies that modulate glutamatergic signaling using a genetic approach, which may have greater target specificity and avoid the side effects of seizures and/ or cognitive deficits that are produced by conventional glutamatergic drugs. Our ongoing studies aim to improve our understanding of why male mice have a higher level of vulnerability to the long-term effects of prenatal stress.

Keywords: Glutamate Receptor, Gene Expression, Sex Differences

Disclosure: Nothing to disclose.

P467. Real-Time fMRI Neurofeedback for Auditory Hallucinations in Schizophrenia Reduces Aberrant Auditory Cortex Activity and Connectivity With the Default Mode Network

Jiahe Zhang, Clemens Bauer, Ann Shinn*, Francesca Morfini, Yoon Ji Lee, Lena Stone, Angelina Awad, Georg Northoff, Margaret Niznikiewicz, Susan Whitfield-Gabrieli

Harvard Medical School, McLean Hospital, Belmont, Massachusetts, United States

Background: Auditory hallucinations (AH) are a core symptom of schizophrenia, can be highly distressing, and do not respond to treatment with antipsychotic medications in 25-30% of schizophrenia patients. Non-pharmacological interventions targeted specifically to AH pathophysiology are critically needed to give AH sufferers greater control over their experiences of AH. According to the resting state hypothesis of AH (Northoff and Qin, 2011), AH may arise from abnormally elevated functional connectivity between the auditory cortex (located in the superior temporal gyrus, STG) and the anterior hub of the default mode network (i.e., medial prefrontal cortex, mPFC), resulting in inappropriately elevated endogenous activity in the auditory cortex as well as heightened attention to, and increase in self-relatedness of internally generated voices. We have previously demonstrated AH reduction following real-time functional magnetic resonance imaging (rt-fMRI) neurofeedback targeting the STG, a technique in which individuals use real-time feedback about STG activity to volitionally modulate activity in that area (Okano et al., 2020). In this randomized sham-controlled study, we sought to investigate the effect of real rt-fMRI neurofeedback (from STG) vs. sham rt-fMRI neurofeedback (from primary motor cortex) on STG activity and STG-mPFC connectivity in schizophrenia patients with AH. We predicted that real, STG neurofeedback but not sham neurofeedback would reduce STG activity and STG-mPFC functional connectivity.

Methods: We acquired data from 25 male and female schizophrenia patients with frequent AH (Positive and Negative Syndrome Scale P3 item ≥ 4). Participants were randomized to receive a single session of either real (n = 12 NFreal) or sham (n = 13 NFsham) rt-fMRI neurofeedback. In the NFreal condition, patients were shown a visual display of real time blood oxygen level dependent (BOLD) activity delivered from their individually localized STG while engaging in a voice recognition task. In the task, pre-recorded voice recordings were played back in the scanner and patients were instructed to upregulate their STG activity by attending to sentences in their own voice and downregulate STG activity by ignoring sentences spoken in a stranger’s voice. Patients in the NFsham condition were given the same instructions (attend to own voice, ignore stranger’s voice) but shown BOLD activity delivered from their motor cortex rather than STG. Immediately before (transfer 1) and after NF (transfer 2), we scanned patients while they engaged in the voice recognition task in the absence of NF. We also acquired resting state fMRI scans before and after NF. We analyzed data from the voice recognition task to investigate within subject pre-post NF changes in STG activity, and the resting state fMRI scans to investigate pre-post NF changes in STG-mPFC functional connectivity.

Results: The paired, pre-post NF t-test in the 12 NFreal patients with neurofeedback delivered from the subject’s individually defined STG showed reduced STG BOLD activation during the voice recognition task in the post-NF (transfer 2) scan relative to the pre-NF (transfer 1) scan (p < 0.002). Paired, pre-post NF t-test in the 13 NFsham patients did not show this effect in STG activity (p < 0.19). In addition, STG-directed NFreal resulted in a reduction in resting state mPFC-STG functional connectivity, computed with mPFC as a seed region, in the NFreal [(t(11) = 5.57, p < 0.001)], but not in the NFsham group [t(12) = 1.41, p < 0.183]. The reduction in mPFC-STG connectivity in the post-NF scan relative to the pre-NF scan was observed in each of the 12 patients who underwent STG-directed NFreal.

Conclusions: These results provide preliminary evidence in support of the resting state hypothesis of AH and suggest that STG-directed real neurofeedback may be effective in decreasing the abnormally elevated STG activity and mPFC-STG connectivity that have been proposed to underlie the experience of AH in individuals with schizophrenia.

Keywords: Real-Time fMRI Neurofeedback, Schizophrenia (SCZ), Auditory Hallucinations, Auditory Cortex, Default Mode Network

Disclosure: Nothing to disclose.

P468. Cell-Type Specific Alterations in Cannabinoid Receptor 1 (CB1) in Patients With Schizophrenia

Shinnyi Chou*, Kenneth Fish, David Lewis, Robert Sweet

University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, United States

Background: Alterations in cannabinoid receptor 1 (CB1) are implicated in schizophrenia. However, previous CB1 receptor ligand binding and immunoreactivity studies showed discrepant results in the prefrontal cortex of schizophrenia. These studies utilized antibodies that preferentially target CB1 at inhibitory boutons, and the exclusion of CB1 measurement in excitatory boutons may underlie the discordant findings. CB1 participates in both depolarization-induced suppression of inhibition and excitation, and understanding cell-type specific CB1 alterations in schizophrenia may increase our insight into its influences on excitatory-inhibitory balance disruptions within the pathology. Here, we investigate CB1 distribution in both inhibitory and excitatory boutons in schizophrenia using quantitative fluorescent microscopy.

Methods: Postmortem tissues containing the dorsolateral prefrontal cortex (DLPFC) from 10 pairs of subjects with schizophrenia and nonpsychiatric comparisons were used. These subject pairs, matched for sex, age, and postmortem interval, were previously found to demonstrate reciprocal alterations between CB1 ligand binding and immunoreactivity study results. Sections were labeled with antibodies for CB1 (validated to target both excitatory and inhibitory boutons), vGlut1 (labeling intracortical excitatory boutons), and vGat (labeling intracortical inhibitory boutons). Fluorescent intensities of CB1 within vGlut1- and vGat- positive boutons were analyzed across all cortical layers using quantitative fluorescence microscopy.

Results: CB1 co-expression with both vGlut1 and vGat were visualized in axons and boutons across all cortical layers. CB1 fluorescent intensity was lower in excitatory boutons compared to inhibitory boutons and exhibited distinct patterns within each cortical layer.

Conclusions: Previous studies examining CB1 alterations in postmortem cortex of subjects with schizophrenia utilized antibodies preferentially targeting CB1 at inhibitory boutons. Using a CB1 antibody that targets both excitatory and inhibitory boutons, we demonstrated distinct cell-type specific distributions of CB1 in the DLPFC of subjects with schizophrenia and nonpsychiatric comparisons. This suggests a possible mechanism by which CB1 dysregulation alters excitatory-inhibitory balance within schizophrenia. Expanding upon these findings, we plan to evaluate cell-type specific CB1 synaptic proteomics in schizophrenia as a potential contributor to the functional disturbances seen in this disorder.

Keywords: Endocannabinoids, Cell Type Specific, Postmortem Brain Tissue

Disclosure: Nothing to disclose.

P469. Multivariate Relationships Between Functional Connectivity and Social Cognitive Performance Across Schizophrenia Spectrum Disorders and Healthy Controls

Lindsay Oliver*, Colin Hawco, Navona Calarco, Iska Moxon-Emre, Thomas Tan, James Gold, George Foussias, Pamela DeRosse, Miklos Argyelan, Robert Buchanan, Anil Malhotra, Aristotle Voineskos

Centre for Addiction and Mental Health, Toronto, Canada

Background: Schizophrenia spectrum disorders (SSDs) often feature social cognitive deficits, associated with functional outcome. Social cognition can be divided into lower-level (e.g., emotion recognition) and higher-level (e.g., theory of mind) processes, subserved by partially dissociable neural networks. Recent work suggests that neural activation patterns during social processing may relate to cognitive performance rather than diagnosis across SSDs and healthy controls. Our objective was to identify multivariate relationships between functional connectivity during a social processing task and social and non-social cognitive performance across individuals with SSDs and healthy controls. We hypothesized that functional connectivity in relevant regions would covary with specific behavioral domains, perhaps reflecting the delineation of lower- and higher-level social cognitive and non-social cognitive constructs.

Methods: Data come from the Social Processes Initiative in the Neurobiology of the Schizophrenia(s) (SPINS) study. Across three sites, 197 people with SSDs and 157 healthy controls (216 males, 138 females) completed the Empathic Accuracy task during functional magnetic resonance imaging, a naturalistic social processing task. Participants also completed measures of lower- and higher-level social cognition and non-social cognition outside the scanner. Partial least squares correlation (PLSC) was used to identify latent variables capturing multivariate brain-behavior relationships with maximal covariance from a ‘brain set’ of functional connectivity metrics (between 392 regions of interest) and a ‘behavior set’ of cognitive performance measures (9 social cognitive and 6 non-social cognitive metrics). Permutation testing (1000 iterations) and bootstrap resampling (1000 iterations) were used to evaluate the significance of identified latent variables, and the reliability of contributing brain and behavior measures, respectively.

Results: PLSC followed by permutation testing identified two significant latent variables (p < .05), explaining 74.0% and 10.3% of the variance, respectively. The first latent variable was characterized by an association between connectivity across much of the brain, including frontal, occipital, temporal, parietal, and subcortical regions, and better performance across both lower- and higher-level social and non-social cognitive measures. The second latent variable was characterized by an association between frontal-parietal and temporal-parietal connectivity, among other regions, and worse social cognitive performance on a subset of lower-level social cognitive measures.

Conclusions: The data-driven delineation of social cognitive constructs is of particular interest given its relationship with functioning and the need to identify treatment targets in SSDs. Our results suggest that patterns of functional connectivity during social processing are associated with both social and non-social cognitive performance across people with SSDs and healthy controls. A general patter