Effect of stress on the voluntary intake of a sweetened ethanol solution in pair-housed adolescent and adult rats

Abstract

Background: Data regarding the effects of stressors on ethanol intake are mixed. Previous experiments reporting greater voluntary intake of ethanol in adolescent than adult rats have examined intake in isolate-housed animals. Given that the stress of isolate housing may differ ontogenetically as well as confound interpretation of other stressor effects, the present study examined stressor/ethanol interactions among pair-housed adolescent and adult rats.

Methods: Sprague-Dawley male rats were implanted with identification tags that allowed individual monitoring of home cage intake of water and either a 10% (v/v) ethanol solution containing 0.1% (w/v) saccharin or saccharin alone over a 14-day access period. Animals were given zero, one, or eight daily 15-min footshock sessions, with shock-induced freezing and pre-, post-, and recovery corticosterone levels determined on the first and last footshock exposure days. After the access period, withdrawal was assessed with a plus maze, and tolerance to ethanol-induced loss of righting reflex was examined.

Results: Nonstressed adolescents drank considerably more sweetened ethanol than did adults, with chronic stress suppressing this adolescent consumption. Ethanol access in adolescents disrupted within-session adaptation to footshock in terms of freezing behavior, although no such disruption was evident at either age when indexed hormonally. Despite relatively high ethanol intakes (up to 6 g/kg/day in the adolescents), no evidence for withdrawal-associated anxiogenesis emerged. Evidence for tolerance was mixed and, to the extent that it was present, was metabolic in nature.

Conclusions: Previous reports of heightened voluntary ethanol intake among adolescent rats are not a function of isolate stress but are evident in pair-housed animals. Adolescents were more sensitive to ethanol/stress interactions than were adults, with the elevated ethanol intake of pair-housed adolescents selectively disrupted by chronic stress, a stress-induced disruption not evident in adults. Likewise, ethanol disrupted behavioral adaptation to the footshock stressor among adolescents but not adults.