Estrogen signaling in the dorsal raphe regulates binge-like drinking in mice

Summary The ovarian hormone estrogens promote binge alcohol drinking and contribute to sex differences in alcohol use disorder. However, the mechanisms for estrogen-induced binge drinking are largely unknown. This study aims to test if estrogens act on 5-hydroxytryptamine neurons in the dorsal raphe nucleus (5-HT DRN ) to promote binge drinking. We used the drinking in the dark (DID) behavioral test in mice to mimic binge drinking in humans. We found that female mice drank more alcohol than male mice in chronic DID tests. This sex difference was associated with distinct alterations in mRNA expression of estrogen receptor α (ERα) and 5-HT-related genes in the DRN, suggesting a potential role of estrogen/ERs/5-HT signaling in binge alcohol drinking. In supporting this view, 5-HT DRN neurons from naïve male mice had lower baseline neuronal firing activity but higher sensitivity to alcohol-induced excitation compared to 5-HT DRN neurons from naïve female mice. Notably, this higher sensitivity was blunted by 17β-estradiol treatment in males, indicating an estrogen-dependent mechanism. We further showed that both ERα and ERβ are expressed in 5-HT DRN neurons, whereas ERα agonist propyl pyrazole triol (PPT) depolarizes 5-HT DRN neurons and ERβ agonist diarylpropionitrile (DPN) hyperpolarizes 5-HT DRN neurons. Notably, both PPT and DPN treatments blocked the stimulatory effects of alcohol on 5-HT DRN neurons in males, despite the fact that they have antagonistic effects on the activity dynamics of 5-HT DRN neurons. These results suggest that ERs’ inhibitory effects on ethanol-induced burst firing of 5-HT DRN neurons may contribute to higher levels of binge drinking in females. Consistently, chemogenetic activation of ERα- or ERβ-expressing neurons in the DRN reduced binge alcohol drinking. These results support a model in which estrogens act on ERα/β to prevent alcohol-induced activation of 5-HT DRN neurons, which in return leads to higher binge alcohol drinking.