Adolescent Stress Increases Adult Ethanol Self-administration and Alters Ventral Tegmental Area GABA Signaling

Alcohol use disorders (AUDs) continue to be a significant public health problem. Early life stress and adversity have long-lasting effects on a wide range of behaviors, including responses to drugs of abuse. Epidemiological evidence indicates that exposure to early life stress contributes to alcohol use disorders and, while it is known that stress and alcohol both act on overlapping mesolimbic circuitry, the cellular mechanisms underlying the relationship between stress and alcohol intake are not well understood. Previous work has demonstrated that acute stress increases ethanol intake mediated by changes in GABA signaling within the ventral tegmental area (VTA). Here we investigated if adolescent stress exposure might elicit long-term, persistent increases in ethanol self-administration associated with altered VTA GABA signaling. To this end, we exposed adolescent postnatal day (PND) 28 male rats to 14 days of chronic variable stress (CVS) and then examined operant ethanol self-administration begun at least 30 days later. We found that adolescent stress exposure resulted in significantly increased ethanol self-administration in adulthood. In contrast, adult (PND 82) male rats exposed to the same CVS protocol did not display increased ethanol self-administration that was begun 30 days later. Furthermore, we found that adolescent stress exposure resulted in enhancement of ethanol-induced GABA signaling onto VTA dopamine neurons and impairments in VTA GABA chloride homeostasis. The results indicate that adolescence is a period vulnerable to stress, which produces long-term changes in VTA GABA signaling associated with increased ethanol self-administration behavior.