Summary Stress hormones elicit profound and complex effects throughout the lifespan, and adolescent brain is particularly sensitive to stressors. One important but understudied question is the sexually dimorphic effects of early life stress. Using mice exposed to prolonged post-weaning social isolation stress, we have found distinct behavioral phenotypes that are reminiscent to human symptoms - elevated aggression in males, and diminished sociability in females. The goal of this project is to understand the physiological and molecular mechanisms underlying the sex-specific divergent effects of chronic adolescent isolation stress. We hypothesize that circuit-specific alterations of neuronal functions in stressed males and females, which are driven by circuit-specific changes in gene expression, mediate the sexually dimorphic consequences of early life stress. To test this, we will use the combination of cutting-edge techniques to address three Specific Aims: (1) To identify differential behavioral and physiological changes induced by stress in male and female mice. A battery of behavioral assays will be made to identify stress-induced phenotypes in both sexes. Slice recordings of synaptic currents and in vivo multichannel recordings of neuronal activity in behaving animals will be performed to examine the involvement of prefrontal cortex (PFC), basolateral amygdala (BLA) and ventral tegmental area (VTA) in the heightened aggression in stressed males and diminished sociability in stressed females. (2) To determine neuronal circuits mediating differential effects of stress in male and female mice. By combining chemogenetic technology to manipulate neuronal activity in specific brain circuits with in vivo recordings of calcium signal and neuronal spikes in behaving animals, we will examine whether the disturbed PFCBLA and PFCVTA pathway after chronic isolation stress plays a causal role in controlling the sexually dimorphic behavioral effects of stress. (3) To investigate molecular mechanisms underlying the circuit-specific effects of stress in male and female mice. We will perform RNAseq to analyze the alteration of mRNA profile in PFC, BLA, and VTA from males and females exposed to adolescent isolation stress to determine molecular basis for the sexually dimorphic effects of stress. We will also use viral-based gene transfer to manipulate key molecules to determine their roles in different aspects of stress effects in both males and females. This proposal will address important issues on neuronal underpinnings of the sex-specific diverse consequences of adolescent stress. The identified mechanisms will offer insights into the development of novel precision therapy to mitigate the distinct deficits in males and females after stress exposure.