How do lateral septum projections to the ventral CA1 influence sociability?

Social dysfunction is a risk factor for several neuropsychiatric illnesses. Previous studies have shown that the lateral septum (LS)-related pathway plays a critical role in mediating social behaviors. However, the role of the connections between the LS and its downstream brain regions in social behaviors remains unclear. In this study, we conducted a three-chamber test using electrophysiological and chemogenetic approaches in mice to determine how LS projections to ventral CA1 (vCA1) influence sociability. Our results showed that gamma-aminobutyric acid (GABA)-ergic neurons were activated following social experience, and that social behaviors were enhanced by chemogenetic modulation of these neurons. Moreover, LS GABAergic neurons extended their functional neural connections via vCA1 glutamatergic pyramidal neurons, and regulating LSGABA→vCA1Glu neural projections affected social behaviors, which were impeded by suppressing LS-projecting vCA1 neuronal activity or inhibiting GABAA receptors in vCA1. These findings support the hypothesis that LS inputs to the vCA1 can control social preferences and social novelty behaviors. These findings provide new insights regarding the neural circuits that regulate sociability.