Developmental differences in the acquisition of tolerance to ethanol.

This study was designed to compare the development of tolerance to ethanol in adolescent and adult rats. Rats were pretreated with ethanol (4 g/kg) twice daily by intragastric gavage for 3 or 7 days, and then challenged with a single IP dose of ethanol (5 g/kg). Throughout the pretreatment period body temperature was measured before and after the morning dosage. During the IP challenge test we measured body temperature, duration of the loss of righting reflex, and blood ethanol level upon regaining the righting reflex. The adolescent rats that were pretreated for 7 days developed greater tolerance to the effects of ethanol on body temperature during the pretreatment period. No tolerance was observed in animals that received only 3 days of pretreatment. Ethanol decreased body temperature to a greater extent in adolescent animals than adults in response to the IP challenge dose, but there was no significant difference between control and pretreated animals in either age group. The time to regain the righting reflex was lower in adolescent rats than in adults. Post hoc analyses indicated that 7 days of ethanol pretreatment diminished the effects of the IP ethanol challenge on the loss of righting reflex in adolescent but not adult rats. Although adolescent rats regained the righting reflex with higher blood ethanol levels than adults, there was no significant effect of ethanol pretreatment on that measure. These findings indicate that the development of tolerance to the temperature regulatory effects of ethanol is more marked in the adolescent rat than in the adult. This developmental difference in ethanol sensitivity is consistent with other recent findings and suggests that adolescence may be a period of unique sensitivity to a number of the behavioral and physiological effects of ethanol.