Aversive effects of ethanol in adolescent versus adult rats: potential causes and implication for future drinking

Many people experiment with alcohol and other drugs of abuse during their teenage years. Epidemiological evidence suggests that younger initiates into drug taking are more likely to develop problematic drug seeking behavior, including binge and other high-intake behaviors. The level of drug intake for any individual depends on the balance of rewarding and aversive effects of the drug in that individual. Multiple rodent studies have demonstrated that aversive effects of drugs of abuse are reduced in adolescent compared to adult animals. In this study, we addressed 2 key questions: First, do reduced aversive effects of ethanol in younger rats correlate with increased ethanol consumption? Second, are the reduced aversive effects in adolescents attributable to reduced sensitivity to ethanol's physiologic effects?

Adolescent and adult rats were tested for ethanol conditioned taste aversion (CTA) followed by a voluntary drinking period, including postdeprivation consumption. Multivariate regression was used to assess correlations. In separate experiments, adolescent and adult rats were tested for their sensitivity to the hypothermic and sedative effects of ethanol, and for blood ethanol concentrations (BECs).

We observed that in adolescent rats but not adults, taste aversion was inversely correlated with postdeprivation consumption. Adolescents also exhibited a greater increase in consumption after deprivation than adults. Furthermore, the age difference in ethanol CTA was not attributable to differences in hypothermia, sedation, or BECs.

These results suggest that during adolescence, individuals that are insensitive to aversive effects are most likely to develop problem drinking behaviors. These results underscore the importance of the interaction between developmental stage and individual variation in sensitivity to alcohol.