Cross-dependence on
ethanol and
pentobarbital was studied in rats reinforced on
diazepam, using an intravenous
self-administration method. Five rats were allowed to self-administer
diazepam 2.0 mg/kg per injection intravenously by pressing a lever on a continuous reinforcement schedule over a 20 day period. The total daily dose of
diazepam delivered reached 50 mg/kg/day. Thereafter,
ethanol (50 or 100 mg/kg per injection) and then
pentobarbital (6 mg/kg per injection) were substituted for
diazepam for 3 and 2 days, respectively. During these substitution periods, responding for
self-administration, food intake and
body weight were recorded. When
ethanol was substituted,
self-administration responding increased and then decreased. Food intake and
body weight also decreased during this period. These changes during the
ethanol substitution session resembled those observed during withdrawal sessions. In contrast, when
pentobarbital was substituted, no significant changes in
self-administration responses, food intake or
body weight were seen. These findings suggest that
diazepam produces cross-dependence on
pentobarbital, but not on
ethanol at the doses used in this experiment.