Accelerated acquisition of ethanol tolerance in isolated mice.

Male mice were kept in isolation (isolated mice) or in groups of 8 mice per cage (grouped mice). After 6 weeks all mice received two daily intraperitoneal injections of 3.5 g/kg ethanol at 8 a.m. and 5 p.m., and sleep time was monitored after the a.m. injection. Brain ethanol levels upon awakening were assayed in sample groups. This procedure was repeated for 3 consecutive days. Isolated mice had a shorter sleep time than grouped mice (p less than 0.001) and they woke up with higher brain ethanol levels (p less than 0.01). Both groups had a progressive decline in sleep time during repeated ethanol exposure (p less than 0.001). However, isolated mice achieved the reduction in half the time it took grouped mice (p less than 0.001). The sleep time significantly correlated with brain ethanol levels upon awakening (r = -0.4967, p less than 0.001). It is suggested, therefore, that isolation in mice reduces brain sensitivity to ethanol and accelerates the rate of acquisition of functional tolerance to ethanol.