Alcohol drinking is attenuated by PDE4 inhibition but partial microglia depletion is not sufficient to block stress-induced escalation of alcohol intake in female mice

Stress is a major contributing factor to binge drinking and development of alcohol use disorders (AUD), particularly in women. Both stress and chronic ethanol can enhance neuroinflammatory processes, which may dysregulate limbic circuits involved in ethanol reinforcement. Clinical and preclinical studies have identified sex differences in alcohol intake in response to neuroinflammatory triggers. Since both cyclic AMP (cAMP) signaling and microglial activation contribute to neuroinflammation, we explored their contribution to stress-induced ethanol drinking in mice. To this end, we first trained C57BL/6J male and female mice to volitionally drink ethanol through a modified version of the "Drinking-in-the-Dark" paradigm. We then assessed whether exposure to foot shock stress followed by repeated exposure to the previously stress-paired context might alter volitional ethanol drinking. We observed that stress exposure resulted in a delayed increase in ethanol intake, but only in female mice. The anti-inflammatory drug Apremilast, an inhibitor of phosphodiesterase type 4 (PDE4; the primary enzyme for cAMP degradation in the brain), reduced ethanol intake and decreased preference for ethanol regardless of stress exposure in females. In contrast, a partial pharmacological depletion of microglia via PLX3397 treatment did not alter baseline ethanol drinking or stress-induced ethanol drinking significantly in female mice. This study shows that female mice are more susceptible to stress-induced ethanol drinking than males, and that this occurs even after partial microglial depletion. In addition, modulation of cAMP signaling by Apremilast administration reduced ethanol drinking regardless of stress exposure, supporting the idea that it might be useful for treatment of AUD.