Project Summary/Abstract Autism spectrum disorder (ASD) is a neurodevelopmental disorder associated with impaired social communications and behavioral abnormalities, which affects ~1 in 54 children in the United States (CDC.gov). SCN2A, encoding neuronal voltage-gated sodium channel Nav1.2, has been identified as one of the leading genes associated with ASD. We have characterized a novel Scn2a-deficient mouse model that is generated via targeted gene-trap knockout (gtKO) strategy and possesses a built-in genetic rescue element. Our preliminary data revealed profound behavioral abnormalities in homozygous Scn2agtKO/gtKO mice including anxiety-like behaviors, impaired nesting and social deficits. We also identified elevated excitation-inhibition (E/I) balance in pyramidal neurons of mPFC, which has been implicated in ASD and social deficits. However, a critical gap exists regarding how in vivo neuronal firings in mPFC are affected by elevated E/I balance and to what extent the manipulation of E/I balance will alter the behavioral outcomes in Scn2agtKO/gtKO mice. To address this gap, we propose to test an overarching hypothesis that Scn2a deficiency increases E/I balance, impairs neuronal responses in mPFC, and results in social deficits that can be rescued with targeted genetic and pharmacological interventions. In Aim 1, we will assess the synaptic properties and in vivo firing of neurons in mPFC using brain- slice patch-clamp recording and Neuropixels in vivo recording. Our findings are expected to provide cellular-level and local network level neuropathological mechanisms of Scn2a deficiency. In Aim 2, we will determine neuronal firings and behavioral outcomes in response to manipulating E/I balance in mPFC microcircuit using optogenetics and chemogenetics. Our findings will bolster the significance of E/I balance modulation for correction of behavioral deficits. In Aim 3, we will evaluate the efficacy of timed genetic and pharmacological rescue to determine optimal windows for intervention. Our study is significant in the following ways: i) SCN2A deficiency to be studied is among the leading monogenetic forms of ASD; ii) Excitation and inhibition (E/I) balance of mPFC microcircuit to be thoroughly dissected is closely associated with social deficits; and iii) Genetic rescue and pharmacological intervention to be tested are of clear clinical relevance, and will provide translational basis to inform therapeutic development for the treatment of Scn2a-deficiency related disorders. Our study has the following innovations: i) use of novel Scn2agtKO/gtKO mice that display profound cellular and behavioral deficits; ii) innovative ways to achieve genetic and pharmacological rescue; and iii) use of cutting-edge technologies including high density Neuropixels in vivo recordings. The applicant is an early stage investigator (ESI), whose team has extensive expertise in sodium channel electrophysiology, animal behaviors, genetics and pharmacology. The team i...