Project Summary Women are more susceptible than are men to stress-related mood and anxiety disorders, underscoring the importance of identifying strategies to promote stress resistance in women. Exercise affords broad benefits to mental health in both sexes, but whether the degree of stress protection and underlying mechanisms differ between sexes is unknown. We recently discovered that female rats are more responsive to the stress-buffering effects of exercise than males. It takes voluntary wheel running (WVR) half the time to enable protection against the depression- and anxiety-like effects of inescapable stress (IS) in female rats (3 wk) than it does in males (6 wk). Enhanced stress protection from exercise in females is an entirely unexplored resilience phenomenon. The goal of this proposal is to examine the sex- and circuit-specific determinants of this process across multiple units of analysis (molecular, cellular, circuits, sex, and behavior). VWR prevents the behavioral sequelae of IS by constraining activation of serotoninergic (5HT) neurons in the dorsal raphe nucleus (DRN) during IS, but the mechanism by which exercise constrains DRN 5HT activity is unknown. Our preliminary data provide strong evidence that stress resistance in both sexes arises from engagement of sensorimotor circuits (dorsolateral striatum; DLS) responsible for maintaining exercise. We have found that the DLS is positioned to inhibit DRN 5HT neurons through a direct GABAergic projection (DLS-DRN circuit), and 6 wk of VWR potentiates the activity of the DLS-DRN circuit during IS. Importantly, although the DLS is required to maintain VWR behavior in both sexes, the DLS governs VWR earlier in females (4 d) than in males (4 wk). Dopamine (DA) in the DLS contributes to DLS-dependent behavior and females are known to have heightened stimulus-evoked dopamine (DA) responses compared to males. This is likely the case with VWR, as just a few bouts of VWR activates D1 receptor-expressing neurons in the DLS of females, but not males. The rapid recruitment of the DLS during VWR in females could accelerate plasticity in the DLS-DRN circuit required for constraining stress-induced 5HT activity. Indeed, stress resistance from 3 wk of VWR in females depends on activity of the DLS-DRN circuit during IS. These data suggest that once exercise becomes governed by the DLS, the DLS-DRN circuit now responds actively to future adversity, thereby inhibiting the DRN & enabling stress resistance. We hypothesize that DLS neural ensembles link exercise to stress resistance and are particularly responsive to exercise in females, due to heightened DA responses to exercise in females compared to males. Intersectional genetic approaches that tag, record, and manipulate neural circuit activity during initial exercise and later stress will be used to 1) identify the role of the DLS in the development of exercise-induced stress resistance and accelerated stress resistance in females, 2) determine the ...