Indiana University-Purdue University Indianapolis (IUPUI) / Mental health is crucially linked to social behavior. A crucial aspect of healthy social behavior involves learning to adapt emotional responses to social cues, for example learning to suppress anxiety through social familiarity, or social familiarity induced anxiolysis (SoFiA). SoFiA is well documented; however, the neural mechanisms of SoFiA are unclear. SoFiA is modeled in rats by employing a social interaction habituation (SI-hab) protocol. Using SI-hab protocol it has been determined that SoFiA represents social safety learning, which requires both anxiogenic stimulus (Anx) and social familiarity (SF) during training sessions (5-6 daily SI sessions), and SoFiA expression is dependent on infralimbic cortex (IL). Based on these findings we hypothesize that Anx and SF are processed by unique neural systems, and repeated convergence of these signals interact within IL to induce plasticity, resulting in social safety learning and anxiolysis. Following SoFiA expression, rats were either sacrificed 30 minutes {for gene expression or Neural Activity Regulated Gene (NARG) analysis} or perfused 90 minutes (for cFos immunoreactivity analysis) after SI session on social training day 5. This led to gaining insights into regions of brain involved in SoFiA response as well as the underlying molecular mechanisms. We identified amygdala, specifically the central amygdala (CeA), basomedial amygdala (BMA) and basolateral amygdala (BLA) as potential candidate regions in SoFiA response. Next, we investigated the role of IL and its efferent pathways in SoFiA expression using inhibitory DREADDs and intersectional chemogenetics to inhibit IL projection neurons and/or axons. We identified that specific projection neurons within the IL are pivotal for SoFiA expression, and that within these projections, the ones that specifically projected to the amygdala are most crucial for expression of SoFiA. / 2021-07-01