Place conditioning: age-related changes in the rewarding and aversive effects of alcohol.

BACKGROUND: Alcohol abuse levels are very high in adolescents, creating a significant societal issue. It has been shown that people who begin alcohol use as adolescents are more likely to become addicts than people who initiate alcohol use as adults. It is important to note that the development of addiction in humans is more rapid with initiation in adolescence than in adulthood.
METHODS: To determine changes in the reinforcing efficacy of alcohol as a function of adolescent development, we used a place-conditioning paradigm. In this study, we assessed the ability of ethanol to support a conditioned place preference (CPP) or aversion. Animals [postnatal days (PND) 25, 35, 45, and 60] were tested for alcohol-induced conditioning in response to a range of ethanol doses (0.2, 0.5, 1.0, and 2.0 g/kg intraperitoneally) or saline.
RESULTS: In general, there was a trend for alcohol to produce an aversion to the ethanol-paired compartment at higher doses. These patterns differed significantly as a function of age. Younger animals (PND 25) exhibited a CPP to a low dose and an aversion at high doses. Late-adolescent (PND 45) animals exhibited a CPP at two moderate doses but a conditioned place aversion at the highest dose. PND 35 and 60 animals did not exhibit a CPP at any examined dose, and PND 60 animals exhibited a progressive aversion with increasing dose.
CONCLUSIONS: The data show that the developmental processes of adolescence influence general responsiveness to alcohol. Specifically, late-adolescent animals (PND 45) seem to prefer doses of alcohol that are either not reinforcing (0.5 g/kg) or are aversive (1.0 g/kg) at other ages. These processes need to be examined thoroughly to understand the development of addiction in adolescence. This is especially important given that alcohol abuse in adolescence may interfere with the usual pattern of brain development as it relates to alcohol reinforcement.