Exploring the effects of adolescent social isolation stress on the serotonin system and ethanol-motivated behaviors.

RATIONALE: Alcohol is one of the most frequently used drugs of abuse and has a major impact on human health worldwide. People assigned female at birth and those with adverse childhood experiences are stress-vulnerable and more likely to report drinking as a means of "self-medication." Prior studies in our laboratory showed that adolescent social isolation stress (SIS) increases vulnerability to ethanol (EtOH) intake and consumption despite negative consequences in female rats. OBJECTIVES: Here, we explored modulation of the dorsal raphe nucleus (DRN)-serotonin (5-HT) system, a sexually dimorphic neurotransmitter system involved in stress-reward interactions, to determine its contribution to EtOH-motivated behaviors in rats that have undergone SIS. RESULTS: We employed electrophysiological and functional neuroanatomy strategies to show that both SIS and EtOH exposure induce persistent hypofunction of the DRN 5-HT system, particularly in females. Chemogenetic activation of DRN 5-HT neurons attenuated reward value for both EtOH and sucrose and elevated punished responding for EtOH in a stress-dependent manner. CONCLUSIONS: Our results highlight an inverse relationship between EtOH consumption and the 5-HT system, the sex- and stress-dependent nature of this relationship, and a connection between DRN 5-HT signaling and acute responding to rewards and punishment. These data support the DRN 5-HT system as a potential target to treat aberrant alcohol consumption and drinking despite negative consequences in stress-vulnerable populations.