Adaptive Under Duress: Endocannabinoid and Glial Control of Stress-Related Behaviors

Abstract

Stress-related psychiatric disorders are characterized by maladaptive defensive responding and impaired regulation of affective state. Although neuronal mechanisms underlying these behaviors have been widely studied, the contribution of neuromodulatory and glial systems remains less defined. This dissertation examines how endocannabinoid (eCB) signaling and astrocyte activity within cortico-limbic circuits regulate threat processing, behavioral flexibility, and acute stress coping. Using systemic pharmacological inhibition to reduce 2-arachidonoylglycerol (2-AG), the behavioral pharmacology portion of this work demonstrates that endogenous 2-AG is a critical determinant of defensive state transitions. In learned threat paradigms, reduced 2-AG heightened both passive and active defensive responses, indicating that endogenous 2-AG normally constrains defensive reactivity as threat imminence escalates. Conversely, during innate threat exposure, reduced 2-AG amplified escape-like responses and diminished exploratory behavior between threats, suggesting that 2-AG promotes flexible behavioral selection according to environmental demands. These findings identify 2-AG as a context-dependent regulator of adaptive threat responses. The second component of the dissertation investigates whether medial prefrontal cortex (mPFC) astrocytes contribute to acute stress coping and whether this depends on astrocytic eCB signaling. In vivo fiber photometry recordings revealed that mPFC astrocytes exhibit robust calcium elevations during exposure to aversive environments and during active stress coping, with activity scaling according to stressor intensity and behavioral effort. Pharmacological reduction of 2-AG attenuated astrocyte calcium responses without altering behavior, indicating sensitivity of astrocyte activity to eCB tone. Selective deletion of cannabinoid receptor type 1 (CB1R) from mPFC astrocytes diminished calcium transient magnitude and spread, altered spontaneous astrocytic activity, and impaired active coping during acute restraint stress, demonstrating that astrocyte CB1R signaling is necessary for proper recruitment of astrocytic networks during aversion. Collectively, these studies identify complementary roles for 2-AG and astrocyte signaling in regulating defensive behavior and acute stress coping. Through integration of behavioral analyses, cell-type–specific manipulations, and in vivo calcium imaging, this dissertation establishes that 2-AG supports context-appropriate defensive state transitions, and that astrocyte CB1R signaling governs mPFC astrocyte engagement during stress. These findings underscore astrocyte–eCB interactions as essential modulators of cortico-limbic function and highlight glial eCB pathways as potential therapeutic targets for stress-related psychiatric disorders.