Adolescent Parvalbumin Expression in the Left Orbitofrontal Cortex Shapes Sociability in Female Mice.

The adolescent social experience is essential for the maturation of the prefrontal cortex in mammalian species. However, it still needs to be determined which cortical circuits mature with such experience and how it shapes adult social behaviors in a sex-specific manner. Here, we examined social-approaching behaviors in male and female mice after postweaning social isolation (PWSI), which deprives social experience during adolescence. We found that the PWSI, particularly isolation during late adolescence, caused an abnormal increase in social approaches (hypersociability) only in female mice. We further found that the PWSI female mice showed reduced parvalbumin (PV) expression in the left orbitofrontal cortex (OFC L ). When we measured neural activity in the female OFC L , a substantial number of neurons showed higher activity when mice sniffed other mice (social sniffing) than when they sniffed an object (object sniffing). Interestingly, the PWSI significantly reduced both the number of activated neurons and the activity level during social sniffing in female mice. Similarly, the CRISPR/Cas9-mediated knockdown of PV in the OFC L during late adolescence enhanced sociability and reduced the social sniffing-induced activity in adult female mice via decreased excitability of PV + neurons and reduced synaptic inhibition in the OFC L Moreover, optogenetic activation of excitatory neurons or optogenetic inhibition of PV + neurons in the OFC L enhanced sociability in female mice. Our data demonstrate that the adolescent social experience is critical for the maturation of PV + inhibitory circuits in the OFC L ; this maturation shapes female social behavior via enhancing social representation in the OFC L SIGNIFICANCE STATEMENT Adolescent social isolation often changes adult social behaviors in mammals. Yet, we do not fully understand the sex-specific effects of social isolation and the brain areas and circuits that mediate such changes. Here, we found that adolescent social isolation causes three abnormal phenotypes in female but not male mice: hypersociability, decreased PV + neurons in the left orbitofrontal cortex (OFC L ), and decreased socially evoked activity in the OFC L Moreover, parvalbumin (PV) deletion in the OFC L in vivo caused the same phenotypes in female mice by increasing excitation compared with inhibition within the OFC L Our data suggest that adolescent social experience is required for PV maturation in the OFC L , which is critical for evoking OFC L activity that shapes social behaviors in female mice.