Time course of elevated ethanol intake in adolescent relative to adult rats under continuous, voluntary-access conditions

Background: Adolescence is a period of elevated alcohol consumption in humans as well as in animal models. Previous studies in our laboratory have shown that adolescent Sprague-Dawley rats consume approximately 2 times more ethanol on a gram per kilogram basis than adult animals in a 2-bottle choice free-access situation. The purpose of the present study was to examine the time course and pattern of elevated ethanol intake during adolescence and the adolescent-to-adult transition, contrast this intake with ontogenetic patterns of food and water intake, and determine whether adolescent access to ethanol elevates voluntary consumption of ethanol in adulthood. Methods:Adolescent [postnatal day (P)27-28] and adult (P69-70) male Sprague-Dawley rats were singly housed with continuous access to both water and 1 of 3 experimental solutions in ball-bearing-containing sipper tubes: unsweetened ethanol (10% v/v), sweetened ethanol (10% v/v+0.1% w/v saccharin), and saccharin alone (0.1% w/v). Results: Ethanol consumption plateaued at approximately 7.5 g/kg/d during the first 2 weeks of measurement (i.e., P28-39) in early adolescence, before declining sharply at approximately P40 to levels that were only modestly elevated compared with adult-typical consumption patterns that were reached by approximately P70. In contrast, intake of food and total calories showed a more gradual decline into adulthood with no distinguishable plateaus in early adolescence. When adolescent-initiated and adult-initiated animals were tested at the same chronological age in adulthood, animals drank similar amounts regardless of the age at which they were first given voluntary access to ethanol. Conclusions: Taken together, these data suggest that the elevated ethanol intake characteristic of early-to-mid adolescence is not simply a function of adolescent-typical hyperphagia or hyperdipsia, but instead may reflect age-related differences in neural substrates contributing to the rewarding or aversive effects of ethanol, as well as possible modulatory influences of ontogenetic differences in sensitivity to novelty or in ethanol pharmacokinetics. Voluntary home cage consumption of ethanol during adolescence, however, was not found to subsequently elevate ethanol drinking in adulthood.