Sex differences in insular cortex function in persistent alcohol drinking despite aversion in mice

One major hallmark of alcohol use disorder (AUD) is the persistence of drinking despite negative consequences. Among indicators of AUD vulnerability, binge drinking has been identified as one of the strongest risk factors. Although the lifetime prevalence of both binge drinking and AUD has historically been higher in men than women, this gap has dramatically narrowed in the last decade. Additionally, sex differences in AUD and binge drinking have been found in clinical and preclinical studies. At the neurobiological level, the insular cortex plays an important role in AUD, with the anterior (aIC) and posterior (pIC) divisions supporting different functions. However, the contributions of the aIC and pIC sections in sexual dimorphism of alcohol binge drinking and the persistence of alcohol drinking despite aversion remain to be uncovered. Using the drinking in the dark model in mice, we validated that female mice have a higher binge ethanol intake compared to males. To evaluate persistent ethanol consumption despite aversion, we supplemented ethanol with the bitter compound quinine, and found a higher persistent drinking in females compared to males. Using fiber photometry recordings, we revealed that aIC activity was increased during binge and persistent ethanol consumption independently of sex, whereas pIC glutamatergic neuron activity was higher during persistent ethanol drinking, specifically in female mice. Using chemogenetics, we revealed that inhibition of aIC glutamatergic neurons reduced intake of bitter solutions independently of the solvent (ethanol or water) in both sexes. In addition, inhibition of pIC glutamatergic neurons exclusively reduced persistent ethanol drinking in females, while decreasing quinine consumption only in males. These findings suggest a sex-dependent function of the pIC in the persistence of ethanol consumption, providing a starting point in understanding sex-specific functions of the insular cortex in the neurobiology of AUD.