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 < 0.001) and they woke up with higher brain ethanol levels (p < 0.01). Both groups had a progressive decline in sleep time during repeated ethanol exposure (p < 0.001). However, isolated mice achieved the reduction in half the time it took grouped mice (p < 0.001). The sleep time significantly correlated with brain ethanol levels upon awakening (r = 0.4967, p < 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.