Sex differences in the microglial response to stress and chronic alcohol exposure in mice

Women are more susceptible to stress-induced alcohol drinking, and preclinical data suggest that stress can increase alcohol intake in female rodents; however, a comprehensive understanding of the neurobiological processes underlying this sex difference is still emerging. Neuroimmune signaling, particularly by microglia, the brain's macrophages, is known to contribute to dysregulation of limbic circuits following stress and alcohol exposure. Females exhibit heightened immune reactivity, so we set out to characterize sex differences in the microglial response to stress and alcohol exposure.

Male and female C57BL/6J mice were administered alcohol over 15 or 22 trials of a modified Drinking in the Dark paradigm, with repeated exposure to inescapable footshock stress and the stress-paired context. Mice were perfused immediately after drinking and we performed immunohistochemical analyses of microglial density, morphology, and protein expression in subregions of the amygdala and hippocampus.

We observed dynamic sex differences in microglial phenotypes at baseline and in response to stress and alcohol. Microglia in the hippocampus displayed more prominent sex differences and heightened reactivity to stress and alcohol. Chronic alcohol exposure decreased density of amygdala microglia and lysosomal expression.

We analyzed multiple measures of microglial activation, resulting in a comprehensive assessment of microglial changes mediated by sex, stress, and alcohol. These findings highlight the complexity of microglial contributions to the development of AUD and comorbid mood and stress disorders in men and women.