Volume 15 Issue 12, December 2012

Sustained activity of Hox5 transcription factors is needed for the development and maintenance of motor neurons that innervate the diaphragm, reports a study in Nature Neuroscience.

A study reconciling contradictory in vitro and in vivo data on neuroligins in synapse formation shows that cell-to-cell variability in neuroligin-1 levels, mediating competition for presynaptic inputs, regulates synapse density.

Using a new retrovirus-optogenetics technique, researchers have found that new neurons in the adult hippocampus are important for memory, but only at an immature stage, when they show enhanced synaptic plasticity.

In this review, the authors examine the link between adult hippocampal neurogenesis and anxiety and depression. They propose that impaired pattern separation underlies the overgeneralization often seen in anxiety disorders.

In this study, the authors show that subjecting adult animals to prolonged social isolation results in impaired heterochromatin formation in oligodendrocytes and decreased myelin thickness, specifically in the prefrontal cortex. This suggests that social experience can regulate myelin plasticity in the adult via an epigenetic program.

The authors report that medium spiny neurons in the mouse nucleus accumbens receive inputs from the cortex, thalamus and hippocampus, but the differential subcellular connectivity of hippocampal inputs makes them much weaker onto neurons in the indirect pathway.

The authors show that the oncogene Bcl6 is necessary for proper cortical neurogenesis in vivo and from embryonic stem cells. BCL6 alters the composition of Notch-dependent transcriptional complexes at the Hes5 promoter, including the recruitment of Sirt1, to promote transition to a neurogenic fate despite active Notch signaling.

In this study, the authors show that Hox5 genes are essential for the organization, survival and axonal branching of motor neurons required for breathing. Unexpectedly, this requirement for Hox5 activity persists to later developmental stages.

The EphB family of receptor tyrosine kinases can signal bidirectionally and functions in a kinase-dependent and kinase-independent manner. To determine the importance of the kinase activity of EphBs for axonal guidance and synaptogenesis, the authors used a chemical genetic method and generated knock-in mice that allow the kinase activity of EphBs to be inhibited without altering kinase-independent functions of EphBs. They find that specific inhibition of EphB kinase activity had no effect on synaptogenesis, but impaired axonal guidance, thereby implicating the kinase function of EphB in one neuronal process, but not other processes that are nevertheless dependent on EphBs.

Ubiquitin proteasome system–mediated, neuronal activity–dependent protein turnover at synapses often occurs in an ensemble fashion where a group or groups of postsynaptic density (PSD) proteins are degraded together in a homeostatic response. This study shows that the synaptic level of the PSD scaffolding protein called GKAP (also known as SAPAP1) is bidirectionally regulated in a homeostatic fashion and is mediated by differential phosphorylation by CaM kinase II isoforms.

The function of neuroligins in regulating synapse formation remains controversial. Here, the authors show that neuroligin-1 (NL1) regulates activity-dependent synaptogenesis and mature synapse number on cortical layer 2/3 pyramidal neurons in vivo. They find that relative differences in transcellular expression of NL1, rather than absolute expression levels, regulate synapse number.

In worms, male exploratory behavior is influenced by two competing needs, food and sex. In this paper, the authors highlight the importance of the pigment dispersing factor signaling pathway in the normal function of a gender-shared neuronal circuit that is involved male-specific reproductive drive.

In this study, the authors used two-photon imaging in macaque monkey to show that orientation and spatial frequency maps are intimately related at a fine spatial scale. They find that the map gradients have a striking tendency toward orthogonality and co-vary negatively from cell to cell at the spatial scale of cortical columns.

Here the authors investigate the neural basis of coherence and contrast detection in the somatosensory system. Model-based analysis of the responses of neurons in the barrel cortex reveal different coding schemes according to the level of correlation in the spatiotemporal patterns of whisker stimulation. The cell populations they find in the primary somatosensory cortex are analogous to cell classes previously reported in two separate cortical areas of the visual system.

Newly generated dentate granule cells in the hippocampus at 4 weeks after their 'birth' are more plastic than existing neurons. The authors use a combined retroviral and optogenetic approach to show that silencing these 4-week-old cells, but not cells of other ages, impaired retrieval of hippocampal memory.

The positive effect of stress on memory formation involves glucocorticoid receptors, but is otherwise not well understood. This article reports that stressful memory consolidation in rats involves the activation of a nongenomic molecular cascade downstream of hippocampal glucocorticoid receptors that overlaps with the BDNF-TrkB signaling pathway.

Brain-machine interfaces (BMIs) have typically focused on performing single-targeted movements. Here the authors report the presence of two subpopulations of neurons in the monkey premotor cortex that allow two planned targets to be simultaneously held in working memory without degradation. They use this finding to develop a BMI that concurrently decodes a full motor sequence in advance of movement and then accurately executes it.

The authors use a computational approach (NETBAG+) to integrate and analyze diverse genetic data and apply this to study schizophrenia-associated genetic variations. They identify gene networks related to axon guidance, synaptic function, cell mobility and chromosomal remodeling.

This study uses EEG in humans to isolate and track an evolving, domain-general decision signal, which varies with accumulated evidence, but is independent of overt actions.

The authors assessed the contributions of early life stress (ELS) and childhood cortisol levels to adolescent resting-state functional connectivity. In females, ELS predicted increased cortisol levels in childhood, which predicted decreased amygdala-ventromedial prefrontal cortex (vmPFC) functional connectivity. Amygdala-vmPFC connectivity was inversely correlated with anxious sympotms and positively correlated with depressive symptoms.

Butko and colleagues report the invention of fluorescent and photo-oxidizing versions of a molecular probe named TimeSTAMP that allows temporal tagging of newly synthesized proteins of interest. The study uses these new tools to track basal and pharmacologically-induced synthesis of the synaptic protein PDS-95 in real time via live fluorescent imaging and/or with ultrastructural resolution using electron microscopy.

Current neural prostheses can translate neural activity into control signals for guiding prosthetic devices, but poor performance limits practical application. Here the authors present a new cursor-control algorithm that approaches native arm control speed and accuracy, permits sustained uninterrupted use for hours, generalizes to more challenging tasks and provides repeatable high performance for years after implantation, thereby increasing the clinical viability of neural prostheses.