Adolescent alcohol exposure decreased sensitivity to nicotine in adult Wistar rats

Many adolescents engage in heavy alcohol use. Limited research in humans indicates that adolescent alcohol use predicts adult tobacco use. The present study investigated whether adolescent intermittent ethanol (AIE) exposure alters nicotine sensitivity in adulthood. Adolescent male Wistar rats (postnatal day 28-53) were exposed to AIE exposure that consisted of 5 g/kg of 25 percent ethanol three times per day in a 2 days on/2 days off regimen. Control rats received water with the same exposure regimen. In adulthood, separate groups of rats were tested for nicotine intravenous self-administration (IVSA), drug discrimination and conditioned taste aversion (CTA). The dose-response function for nicotine IVSA under a fixed-ratio schedule of reinforcement was similar in AIE-exposed and control rats. However, AIE-exposed rats self-administered less nicotine at the lowest dose, suggesting that low-dose nicotine was less reinforcing in AIE-exposed, compared with control rats. AIE-exposed rats self-administered less nicotine under a progressive-ratio schedule, suggesting decreased motivation for nicotine after AIE exposure. The discriminative stimulus effects of nicotine were diminished in AIE-exposed rats compared with control rats. No group differences in nicotine CTA were observed, suggesting that AIE exposure had no effect on the aversive properties of nicotine. Altogether, these results demonstrate that AIE exposure decreases sensitivity to the reinforcing, motivational and discriminative properties of nicotine while leaving the aversive properties of nicotine unaltered in adult rats. These findings suggest that drinking during adolescence may result in decreased sensitivity to nicotine in adult humans, which may in turn contribute to the higher rates of tobacco smoking.