Comparative effects of ethanol on motor activity and operant behavior

Ethanol effects on two types of motor activity and on lever responding for food delivered on a fixed-ratio 20 (FR 20) reinforcement schedule were compared using C57BL/6 (C57) mice. Low doses of ethanol (1-2 g/kg) transiently elevated horizontal activity and high doses (2.5 and 3.0 g/kg) reduced this behavior throughout testing with a slight recovery toward the end of a 16-min test period. In contrast, similar ethanol doses produced a monotonic reduction in both vertical activity and lever responding for food under the FR 20 schedule. The ethanol-induced reduction in FR 20 lever responding was less prolonged than the reduction in vertical activity but was more prolonged than the reduction in horizontal activity. Because vertical activity and lever responding for food delivered on the FR 20 schedule were never elevated, were reduced at ethanol doses that either stimulated or depressed horizontal activity, and were unaffected by low ethanol doses that did not affect horizontal activity, it is unlikely that either are sensitive to the stimulatory effects of ethanol. Accountable mechanisms for the different effects of ethanol on the three behaviors are unknown; however, the present study eliminates ethanol dose, postinjection time, testing time, and food deprivation condition as possible reasons for the differences.