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A circuit from hippocampal CA2 to lateral septum disinhibits social aggression


Although the hippocampus is known to be important for declarative memory, it is less clear how hippocampal output regulates motivated behaviours, such as social aggression. Here we report that pyramidal neurons in the CA2 region of the hippocampus, which are important for social memory, promote social aggression in mice. This action depends on output from CA2 to the lateral septum, which is selectively enhanced immediately before an attack. Activation of the lateral septum by CA2 recruits a circuit that disinhibits a subnucleus of the ventromedial hypothalamus that is known to trigger attack. The social hormone arginine vasopressin enhances social aggression by acting on arginine vasopressin 1b receptors on CA2 presynaptic terminals in the lateral septum to facilitate excitatory synaptic transmission. In this manner, release of arginine vasopressin in the lateral septum, driven by an animal’s internal state, may serve as a modulatory control that determines whether CA2 activity leads to declarative memory of a social encounter and/or promotes motivated social aggression.

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Fig. 1: CA2 projections to the lateral septum.
Fig. 2: Silencing of CA2 or the CA2–LS projection inhibits social aggression.
Fig. 3: dLS neurons are excited by dCA2 projections and inhibit vLS cells.
Fig. 4: Silencing CA2 with iDREADD expression and CNO injection decreases c-Fos expression in VMHvl.
Fig. 5: CA2 pyramidal neurons respond to diverse social encounters whereas CA2 terminals in LS selectively convey aggression-related information.
Fig. 6: AVPR1b activation on CA2 presynaptic terminals in LS potentiates synaptic excitation and increases social aggression.

Data availability

All analysed data supporting this study are presented in the form of graphs. All raw records used in the analysis are available from the corresponding author in response to reasonable requests.


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We thank N. Renier, the Rockefeller imaging center and the laboratories of F. Polleux and T. Jessell for their help in creating Supplementary Video 1. We also thank R. Bruno, L. Herbaut and the members of the Siegelbaum laboratory for discussions. This work was supported by the R01 MH104602 and R01 MH106629 from NIH (S.A.S.), PD/BD/113700/2015 from the Portuguese Foundation for Science and Technology (T.M.), 5TL1TR001875-03 from NIH (E.W.B.) and the HHMI (E.R.K).

Reviewer information

Nature thanks S. Dudek, C. Gross and D. Lin for their contribution to the peer review of this work.

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Authors and Affiliations



Conceptualization: F.L. and S.A.S. Viral injections: F.L., D.H.B. and T.M. Immunohistochemistry: F.L., D.H.B. and L.M.B. Intracellular recordings: F.L. Behavioral assays: F.L., J.P., T.M. and L.B. Fibrephotometry: F.L. and A.A. 3D representation: F.L. and E.W.B. Writing (original draft): F.L. Writing (review and editing): F.L., S.A.S. and E.R.K. Visualization: F.L. Supervision: S.A.S. and E.R.K. Funding acquisition: S.A.S. and E.R.K.

Corresponding authors

Correspondence to Felix Leroy or Steven A. Siegelbaum.

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Extended data figures and tables

Extended Data Fig. 1 CA2 projections to LS.

ac, Diagram and horizontal sections from an Amigo2-Cre mouse brain injected with rAAV5-EF1a-DIO-hChR2(E123T/T159C)-eYFP into dCA2. The arrowhead in b shows the dCA2 axons extending up to the dLS. Drawing in a was inspired by ref. 49. c, More ventral, showing the projection from dCA2 to LS and to the ventral hippocampus. d, e, Diagram and enlarged view of a coronal dLS section from an Amigo2-Cre mouse brain injected into dCA2 with rAAV5-mGFP-p2A-synatophysin-mCherry, labelling dCA2 projections (green) and presynaptic terminals (red). fh, Coronal sections of an Amigo2-Cre mouse brain injected unilaterally with rAAV5-EF1a-DIO-hChR2(E123T/T159C)-eYFP into the right CA2 area. f, Hippocampal section. g, h, LS sections. Three mice were injected per experiment. All mice presented similar staining patterns. Scale bars, 500 µm except e, 20 µm.

Extended Data Fig. 2 dCA3 and dCA2 project to different but overlapping regions of LS.

a, b, rAAV5-EF1a-DIO-hChR2(E123T/T159C)-eYFP was injected into the hippocampal dCA3 region of a Grik4-Cre mouse (a) and the dCA2 region of an Amigo2-Cre mouse (b). cf, Hippocampal (c, d) and LS coronal (e, f) sections. g, h, Horizontal LS sections. m.f., mossy fibre. Three mice were injected per experiment. All mice presented similar staining patterns. Scale bars, 200 µm except inset in c, 50 µm.

Extended Data Fig. 3 CTB and rabies virus injections in dLS confirm the CA2–LS projection.

a, Atlas drawing (reproduced with permission50) of the CTB-488 injection site. bd, Hippocampal coronal sections following injection of CTB (green) into right LS and labelled for PCP4 (red); blue, DAPI staining. b, Whole hippocampi. c, d, High-magnification views of CA2 region in ipsilateral (c) and contralateral (d) hippocampus. Three mice injected. e, Coronal section of LS injected with G-deleted rabies virus (green). f, g, Locally infected cells (arrowheads, green) enlarged and labelled for GABA immunofluorescence (arrows, purple). Three mice were injected per experiment. All mice presented similar staining patterns. Scale bars, b, e, 500 µm, c, d, 50 µm, f, g, 100 µm.

Extended Data Fig. 4 dCA2 pyramidal neurons project to both dCA1 and LS.

a, Dual retrograde staining of dCA2 by injection of HSV-LSL1–mCherry into dCA1 and CTB-488 into dLS of an Amigo2-Cre mouse. b, Hippocampal coronal section following injections as in a and labelled for RGS14 (blue). Arrowheads denote single-labelled cells (green or red) and arrows dual-labelled ones (white). Scale bar, 50 µm. c, Quantification of the percentage of CA2 pyramidal neurons that project to either dLS or dCA1. Because retrograde labelling efficiency is not complete, the fraction of labelled cells provides a lower limit on the fraction of dCA2 pyramidal neurons that project to these regions (12 sections from 6 mice in each group). Bars show mean ± s.e.m. d, Comparison of the expected percentage of dual-labelled CA2 pyramidal neurons versus the observed percentage. The fraction of dual-labelled cells (21 ± 4%) was almost identical to the fraction predicted under the assumption of random retrograde labelling of a single population of CA2 pyramidal neurons, each of which sends a projection to CA1 and LS ([fraction of labelled CA1 projecting cells] × [fraction of labelled LS projecting cells] = 0.55 × 0.44 = 24%). This is similar to results suggesting that a uniform population of CA3 pyramidal neurons projects to both LS and CA151. Thus, it is likely that a single population of CA2 pyramidal cells projects to both LS and CA1. Two-sided Wilcoxon test, P = 0.2. Black dots, individual mice (n = 6). Red dots with error bars, mean ± s.e.m.

Extended Data Fig. 5 Analysis of light-evoked synaptic responses with ChR2–eYFP expressed in dCA2 pyramidal neurons.

a, Schematic of hippocampal or septal slice recordings from Amigo2-Cre mouse injected into dCA2 with rAAV5-EF1a-DIO-hChR2(E123T/T159C)-eYFP (5 cells from 3 mice). b, CA2 pyramidal neuron voltage response under current-clamp to a 20-Hz train of 1-ms light pulses. Scale bars, 20 mV and 200 ms. c, dCA2 pyramidal neuron current responses under voltage-clamp with increasing light stimulation intensity (onset at blue spot). Negative (excitatory) currents plotted upwards. Responses to different light intensities coloured as in d. Note action currents reflecting escaped action potentials with two highest light intensities. Scale bars, 1 nA and 5 ms. d, Input–output curve for light-induced current in ChR2-expressing dCA2 pyramidal neurons. e, Schematic of dLS synaptic voltage recordings in septal slice from Amigo2-Cre mouse injected with the same virus as in a. f, g, Maximal dLS PSP amplitude (f) and latency (g) following light stimulation (65 cells from 32 mice; mean ± s.e.m.). h, Quantification of effect of GABAA and GABAB receptor antagonist application (1 µM SR 95531 and 2 µM CGP 55845, respectively) on light-induced PSP amplitude in dLS showing individual cells (black, 6 cells from 4 mice) and mean ± s.e.m. (red). Two-sided Wilcoxon test, *P = 0.03. Scale bars, 2 mV and 100 ms. i, Light-induced PSP amplitude in dLS before and after application of NMDA and AMPA receptor antagonists 25 µM AP5 and 20 µM CNQX, respectively (6 cells from 3 mice). Two-sided Wilcoxon test compared to baseline, P = 0.03. Scale bars, 5 mV and 100 ms. j, vLS recording under same conditions as in a and e. k, Amplitude of light-induced IPSCs in vLS before and after application of 25 µM AP5 and 20 µM CNQX (6 cells from 3 mice). Two-sided Wilcoxon test, P = 0.03. Scale bars, 200 pA and 100 ms.

Extended Data Fig. 6 Effect of CA2 silencing on aggression attack parameters.

Amigo2-Cre (Cre) mice and wild-type littermates (WT) were injected into dCA2 with rAAV2-hsyn-DIO-HA-hM4D(Gi)-IRES-mCitrine (AAV-DIO-iDREADD). After 3 weeks, mice were injected intraperitoneally with CNO or saline and, 30 min later, subjected to the resident–intruder test. ad, Mean (± s.e.m.) number of bites (a), number of attack bouts (b), attack duration (c) and number of tail rattles (d). Grey dots, individual mice (29, 29, 43 and 34 mice from left to right for all bar graphs). Two-sided Mann–Whitney tests: *P = 0.011; **P = 0.096; *P = 0.012; and *P = 0.041, for ad, respectively.

Extended Data Fig. 7 Behavioural controls for CA2 silencing.

Amigo2-Cre mice (Cre) and wild-type littermates (WT) were injected into dCA2 with rAAV2-hsyn-DIO-HA-hM4D(Gi)-IRES-mCitrine. After 3–4 weeks for viral expression, mice were given CNO (10 mg kg–1) intraperitoneally 30 min before behavioural testing. ad, Open field testing. a, Distance travelled. b, Heat maps of time spent at each position for a wild-type and an Amigo2-Cre mouse (all 25 mice showed similar heat maps). c, Time spent in centre and surround. d, Ratio of the time spent in surround/centre. e, Time spent interacting with a novel object. f, Time spent interacting with a novel mouse. g, Stacked bar charts of the distributions of mice that attacked or only explored the cricket in prey aggression test. h, Latency to attack the cricket. Grey dots, individual mice (14 wild-type and 11 Amigo2-Cre mice). Bars show mean ± s.e.m.

Extended Data Fig. 8 Silencing dCA2 inputs to dLS by CNO application reduces PSP in dLS neurons evoked by photostimulation.

a1, Co-expression of iDREADD and ChR2 in CA2 pyramidal neurons. a2, Left, light-evoked PSP in dLS neuron before and after bath application of 5 µM CNO. Scale bars, 1 mV and 100 ms. Right, quantification of effect of CNO on peak PSP amplitude showing individual cells (black, 7 cells from 3 mice) and mean ± s.e.m. (red). Two-sided Wilcoxon test, *P = 0.02. b, Schematic (b1) and LS coronal section (b2) from an Amigo2-Cre mouse expressing iDREADD and mCitrine in CA2 pyramidal neurons and implanted with a cannula in LS. Mouse was infused with 1 µl miniRuby through the cannula 15 min before death. Labelling shows mCitrine expression (green) and miniRuby (red). Scale bar, 400 µm.

Extended Data Fig. 9 Hippocampal retrograde labelling following HSV injection into VMH.

a, Schematic of the experiment. bd, Coronal sections after injection of the retrograde trans-synaptic tracer HSV CMV–mCherry into VMH. Note the labelling in dorsal and ventral LS (c) and dCA2 (d). Three mice injected. All mice presented a similar staining pattern. Scale bars, b, c, 100 µm, d, 40 µm.

Extended Data Fig. 10 VMHvl c-Fos quantification controls.

a, Representative images of c-Fos immunofluorescence in VMH following bouts of aggression 30 min after intraperitoneal injection of CNO or saline in wild-type or Amigo2-Cre mice (all groups previously injected in CA2 with rAAV2-hsyn-DIO-HA-hM4D(Gi)-IRES-mCitrine). Scale bars, 400 µm. b, Number of c-Fos-expressing cells in VMHvl of wild-type mice killed 1 h after indicated behaviours. Coloured dots, individual mice (5, 6 and 9 mice). Bars show mean ± s.e.m. Kruskal–Wallis test χ2 = 15.16, P < 0.0001 followed by Dunn’s multiple comparison tests, ***P = 0.0006 and *P = 0.01. c, Each mouse was challenged with a resident–intruder test once every 5 days until it showed aggression, after which it was killed. Grey dots, individual mice (7, 8, 7 and 13). Bars show mean ± s.e.m. Two-way ANOVA: F = 7.4, *P = 0.01.

Extended Data Fig. 11 Fibre photometry measures of CA2 pyramidal neuron GCaMP6f signals during social interactions.

a, GCaMP6f fluorescence signal as a function of mouse velocity. Pearson test of correlation (r) performed on n = 5,332 1-s time bins. Note the lack of correlation (P = 0.7). Lack of correlation was observed in all mice. b, GCaMP6f responses with fibre over CA2 pyramidal neuron soma during indicated social behaviour (calculated from the mean signal during each episode). Each point represents an episode (49, 31 and 20 episodes from left to right collected from 5 mice). Two-sided one-sample t-tests; ****P < 0.001, ***P = 0.0001. c, As in b with fibre over CA2 pyramidal neuron terminals in LS (34, 27 and 23 episodes collected from 6 mice). Bars show mean ± s.e.m. Two-sided one-sample t-test; ****P < 0.001. dj, GCaMP6f responses from CA2 somata during various social and non-social behaviours. GCaMP6f recording from CA2 pyramidal neurons in hippocampus during: exploration of a novel environment (d), exploration of a novel object (e), feeding (f), exploration of a female (g), and predator–prey aggression (h). Bar graphs of the GCaMP6f responses during each type of social interaction (calculated from the maximum (i) or the mean (j) signal during each episode). Each point represents an episode except for the novel environment, where episodes were defined as 10-s bins (60, 27, 17, 27, 34, 21, 43, 19 episodes from left to right collected from 6 mice). Bars show mean ± s.e.m. Two-sided one-sample t-tests for i; *P = 0.03, *P = 0.02, *P = 0.047 and ****P < 0.0001 from left to right. Two-sided one-sample t-tests for j; **P = 0.003, ****P < 0.0001, **P = 0.002 and ****P < 0.0001 from left to right. km, Behaviour and GCaMP6f responses from dCA2 pyramidal neuron somata during multiple presentations of an ovariectomized female. k, Time (mean ± s.e.m.) spent in social exploration of the same novel female presented in trials 1–4 and a second novel female in trial 5 (4 mice). Resident males normally engaged in non-aggressive social exploration of the female during each exposure, with exploration time showing a trend to decrease during successive trials as a result of increased familiarity. Introduction of a novel female in trial 5 resulted in enhanced social exploration, indicating that the decrease in exploration of the same female represents social memory formation, and not fatigue or disinterest. We previously found that this behaviour required dCA213. Two-sided t-test, **P = 0.005. l, m, Peak (l) and mean (m) GCaMP6f responses recorded from CA2 pyramidal neurons in hippocampus during each period of social exploration in each trial (10, 12, 20, 23 and 26 episodes collected from 4 mice; mean ± s.e.m.). Fibre photometry recordings show that dCA2 responds during social exploration of the female in the familiarization trials, with a trend for activity to decrease with increased familiarization. Introduction of the novel female produced a statistically significant increase in the dCA2 GCaMP6f signal (trial 5). Two-sided t-tests: *P = 0.048 (l) and *P = 0.039 (m).

Extended Data Fig. 12 Neuromodulation of the CA2-LS synapse by AVP.

a, ChR2 expression in dCA2 pyramidal neurons. b, Paired-pulse ratios (right) of PSP amplitudes evoked by two light pulses separated by 50 ms (left), before and after 100 nM AVP (19 cells from 10 mice). Black dots, individual cells; red dots, mean ± s.e.m. Two-sided Wilcoxon test, ****P < 0.0001. Scale bars, 2 mV, 100 ms. c, Example time course of PSPs in dLS evoked by photostimulation of ChR2-expressing dCA2 projections. Grey bar shows period of bath application of 250 nM TGOT. d, PSP amplitudes before and 30 min after application of 250 nM TGOT (7 cells from 3 mice). Black dots, individual cells; red dots, mean ± s.e.m. Two-sided Wilcoxon test, P = 0.3.

Supplementary information

Reporting Summary

Video 1: 3D visualization of the CA2-LS projection.

3D brain reconstruction from Amigo2-Cre mouse injected in dCA2 with rAAV5-EF1a-DIO-hChR2(E123T/T159C)-eYFP (3 mice) showing the dCA2 to LS projection. Brains were cleared using iDISCO. All experiments yielded similar results.

Video 2: Example of behaviors during the resident-intruder test.

WT littermate mouse following infusion of CNO in dLS. Only behaviors observed for the resident (black mouse) are described (in italics) with our classification above. Note the progression from exploration to dominance and then attack. All resident-intruder tests were normally performed in low-light conditions with cage lid on, in an isolation chamber.

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Leroy, F., Park, J., Asok, A. et al. A circuit from hippocampal CA2 to lateral septum disinhibits social aggression. Nature 564, 213–218 (2018).

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  • Social Aggression
  • Lateral Septum (LS)
  • Resident Intruder Test
  • Fiber Photometry
  • Secondary Incubation

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