The VGLUT3-p.T8I Mutation Alters Striatal Acetylcholine Dynamics in Response to Social Stressors and Drives Selective Social Avoidance in Male Mice

The nucleus accumbens (NAc) is a key structure translating dopaminergic inputs into social avoidance following repeated social defeat. Within the NAc, dopamine (DA) release is modulated in part by cholinergic interneurons (CINs). CINs express the vesicular glutamate transporter type 3 (VGLUT3), which supports glutamate co-release and regulates vesicular acetylcholine (ACh) loading, thereby fine-tuning cholinergic signaling. A rare human VGLUT3-p.T8I missense variant is associated with compulsive behaviors toward food and drugs of abuse. We hypothesized that p.T8I disrupts NAc ACh dynamics and affects social avoidance following social defeat. Male and female mice expressing the VGLUT3-p.T8I variant were exposed to a 10-day chronic social defeat stress (CSDS) paradigm. Social avoidance toward the aggressor strain and a C57BL/6 (B6) conspecific was measured using the social interaction and 3-chamber tests, and anxiety-like behavior was evaluated in the elevated zero maze. Fiber photometry was used to monitor ACh and DA dynamics in the NAc medial shell (NAcMsh) during CSDS and social interaction. After CSDS, VGLUT3T8I/T8I males showed aggressor strain-specific social avoidance and increased anxiety-like behavior compared to WT mice. Mutants showed blunted CSDS-induced ACh increase during attacks but enhanced ACh release upon re-exposure to the CD1 aggressor strain correlating with avoidance severity. DA dynamics were minimally affected. Females, regardless of genotype, displayed a male-mutant-like phenotype. In males, the VGLUT3-p.T8I variant alters NAcMsh ACh signaling and promotes selective social avoidance toward aggressors and elevated anxiety after CSDS, highlighting a potential cholinergic mechanism underlying stress-induced social avoidance with broader relevance to psychiatric disorders.