Estrogen signaling in the dorsal raphe regulates binge-like drinking in mice
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-HTDRN) 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 (ER) 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-HTDRN neurons from naive male mice had lower baseline neuronal firing activity but higher sensitivity to alcohol-induced excitation compared to 5-HTDRN neurons from naive female mice. Notably, this higher sensitivity was blunted by 17{beta}-estradiol treatment in males, indicating an estrogen-dependent mechanism. We further showed that both ER and ER{beta} are expressed in 5-HTDRN neurons, whereas ER agonist propyl pyrazole triol (PPT) depolarizes 5-HTDRN neurons and ER{beta} agonist diarylpropionitrile (DPN) hyperpolarizes 5-HTDRN neurons. Notably, both PPT and DPN treatments blocked the stimulatory effects of alcohol on 5-HTDRN neurons in males, despite the fact that they have antagonistic effects on the activity dynamics of 5-HTDRN neurons. These results suggest that ERs inhibitory effects on ethanol-induced burst firing of 5-HTDRN neurons may contribute to higher levels of binge drinking in females. Consistently, chemogenetic activation of ER- or ER{beta}-expressing neurons in the DRN reduced binge alcohol drinking. These results support a model in which estrogens act on ER/{beta} to prevent alcohol-induced activation of 5-HTDRN neurons, which in return leads to higher binge alcohol drinking.