Ethanol Self-Administration Reduces mGlu2/3 Protein Expression Specifically in the Nucleus Accumbens and mGlu2/3 Activation Suppresses Binge Drinking.

Background: Alcohol use disorder is associated with dysregulated glutamatergic signaling within mesocorticolimbic circuits that govern reinforcement and excessive ethanol intake. Group II metabotropic glutamate receptors (mGlu2/3) act primarily as presynaptic autoreceptors that regulate glutamate release. However, how voluntary alcohol intake alters mGlu2/3 expression within reward circuitry remains unclear. Methods and Results: We examined the effects of operant alcohol self-administration on mGlu2/3 protein expression and assessed the functional impact of group II receptor modulation on binge-like ethanol intake. Male C57BL/6J mice self-administered sweetened ethanol or sucrose under behaviorally matched conditions for 35 days. Immediately after the final session, tissue punches from the nucleus accumbens (NAc), amygdala, and prefrontal cortex were collected for Western blot analysis. Operant ethanol self-administration selectively reduced mGlu2/3 protein expression in the NAc, with no changes detected in the amygdala or prefrontal cortex. Both monomeric and dimeric mGlu2/3 protein levels were reduced, and a composite index revealed coordinated downregulation of receptor expression. In separate cohorts, systemic administration of the mGlu2/3 agonist LY379268 dose-dependently reduced binge-like ethanol intake in a limited-access home-cage drinking model, whereas positive allosteric modulation of mGlu2 receptors with LY487379 was ineffective. Conclusions: These results show that low-dose operant ethanol self-administration produces an ethanol- and region-specific reduction of mGlu2/3 protein expression in the NAc and that pharmacological activation of group II receptors, potentially involving mGlu3-specific receptors, is sufficient to suppress binge-like ethanol consumption. These data identify presynaptic mGlu2/3 dysregulation as a mechanism contributing to ethanol-related behaviors and support group II metabotropic glutamate receptors as therapeutic targets for alcohol use disorder.