Abstract
BACKGROUND: Despite the fact that adolescent rats have repeatedly been found to consume more ethanol than adult rats in a variety of ethanol access paradigms, the exact cause of the increase in ethanol consumption during adolescence is not known. One possibility is that age differences in sensitivity to ethanol's rewarding effects may contribute to the elevated intake seen among adolescents. Human studies have shown that autonomic effects of ethanol, particularly ethanol-induced tachycardia, are correlated with the positive hedonic properties of the drug and, hence, may serve as a biomarker for reward. METHODS: In this experiment, a limited-access self-administration paradigm was used to examine the autonomic effects of ethanol in outbred male adolescent and in adult Sprague-Dawley rats under circumstances likely to reveal the rewarding value of ethanol. RESULTS: The results indicated that voluntary ethanol consumption was greater in adolescent than adult rats and that only adolescents consumed enough of the saccharin-sweetened ethanol solution to show a tachycardic effect greater than that seen in response to saccharin alone. CONCLUSIONS: To the extent that these tachycardic properties of ethanol are associated with the rewarding/hedonic properties of ethanol as previously reported in humans, these findings support the suggestion that adolescent animals may have found the ethanol-containing solution to be more rewarding than the saccharin solution. A similar effect was not seen in adults, findings consistent with the notion that adult rats may not consume enough ethanol under these circumstances to experience its positive rewarding properties.