Neurexin-3 defines synapse- and sex-dependent diversity of GABAergic inhibition in ventral subiculum

Abstract

Ventral subiculum (vSUB) is integral to the regulation of stress and reward, however, the intrinsic connectivity and synaptic properties of the inhibitory local circuit are poorly understood. Neurexin-3 (Nrxn3) is highly expressed in hippocampal inhibitory neurons, but its function at inhibitory synapses has remained elusive. Using slice electrophysiology, imaging, and single-cell RNA sequencing, we identify multiple roles for Nrxn3 at GABAergic parvalbumin (PV) interneuron synapses made onto vSUB regular spiking (RS) and burst spiking (BS) principal neurons. Surprisingly, we found that intrinsic connectivity of vSUB and synaptic function of Nrxn3 in vSUB are sexually dimorphic. We reveal that vSUB PVs make preferential contact with RS neurons in males, but BS neurons in females. Furthermore, we determined that despite comparable Nrxn3 isoform expression in male and female PV neurons, Nrxn3 maintains synapse density at PV-RS synapses in males, but suppresses presynaptic release at the same synapses in females.

Ventral subiculum inputs to nucleus accumbens medial shell preferentially innervate D2R medium spiny neurons and contain calcium permeable AMPARs

“…Although vSUB is composed of about 50% RS and 50% BS neurons (Staff et al, 2000; Graves et al, 2012), we found that the majority of NAcMS-projecting neurons in vSUB were RS neurons (70% ± 4) (Figure 1G), which is remarkably consistent with other studies using different retrograde labeling approaches such as retrobeads or cholera toxin B (Kim & Spruston, 2012; Lee et al, 2019). In light of our recent findings that the wiring of vSUB local circuitry is sexually dimorphic (Boxer et al, 2021), we reviewed whether the wiring of the vSUB-NAcMS circuit also exhibits sexual dimorphism. We separated our AAV 2 rg-mRuby experiment by sex but found that equivalent proportions of RS/BS neurons project to NAcMS in male and female mice (%RS: female: 66 ± 4, male: 75 ± 6; U = 2, p = 0.40, Mann-Whitney) (Figure 1G, females: closed circles, males: open circles).…”

“…Finally, the sexually dimorphic organization of vSUB local circuitry (Boxer et al, 2021) prompted us to ask whether the vSUB-specific bias for D2R MSNs was sex-specific. We separated our data by sex but found no sex differences (effect of sex: ns, effect of cell-type: F(1,29) = 6.913, p = 0.014, effect of interaction: ns, Ordinary Two-way ANOVA) (Figure 2C, females: closed circles, males: open circles).…”

“…Our recent work identified sex differences in PV-mediated inhibition of vSUB RS vs BS neurons and here we tested whether vSUB synapses in dorsal NAcMS also exhibit sexual dimorphism (Boxer et al, 2021). We assessed sex differences throughout our study, but found no differences in any of the circuit or synaptic properties measured.…”

“…At P56-65, animals were deeply anesthetized with isoflurane and decapitated. Brains were rapidly dissected and 300 μm horizontal slices (for vSUB recordings) or coronal slices (for NAc recordings) were sectioned with a vibratome in cutting solution then moved to ACSF, as previously described (Boxer et al, 2021), were superfused with 29.5°C oxygenated ACSF containing (in mM) 126 NaCl, 26.2 NaHCO 3 , 11 D-Glucose, 2.5 KCl, 2.5 CaCl 2 , 1.3 MgSO 4 -7H 2 O, and 1 NaH 2 PO 4 . For NAc recordings, ACSF included 100 μM picrotoxin.…”

“…Distinct from vCA1, vSUB comprises two classes of excitatory principal neurons identified electrophysiologically as regular or burst spiking (RS or BS) cells. RS and BS neurons are equally represented in vSUB but exhibit distinct gene expression, connectivity, plasticity, and behavioral functions (Wozny et al, 2008; Cembrowski et al, 2018; Boxer et al, 2021; Böhm et al, 2015; Graves et al, 2012). Thus, RS and BS vSUB neurons may provide distinct input to dorsal NAcMS and possess unique synaptic properties compared to other subregions of vHIPP.…”