Discrimination between oral amobarbital and diazepam effects in rats

Amobarbital (40 mg/kg) and diazepam (8 mg/kg) were orally intubated in 8 male and 8 female rats 60 min before the 10‐min discrimination sessions. Presses on different levers, depending on the drug given, were reinforced by food pellets on a 10‐sec fixed interval schedule. Within 27 sessions, divided between the 2 drugs, the rats made reliably more than 50% of their presses on the reinforced lever prior to the first food pellets of the session. Additional training sessions included higher doses of both drugs (60–120 mg/kg amobarbital; 12–32 mg/kg diazepam). The amobarbital choice predominated after the high amobarbital doses (80–120 mg/kg) but was close to 50% after all diazepam doses. Response rates were decreased by the highest doses of amobarbital but not diazepam. In a subgroup of 7 high‐dose discriminators, the reinforced lever was predominantly chosen after high doses of either drug. In a subgroup of 7 high‐dose nondiscriminators, the high diazepam doses induced a majority of amobarbital choices but the high amobarbital doses induced a greater preponderance of amobarbital choices. The discriminative performance by both subgroups indicated qualitatively different effects of the 2 drugs in spite of their similar sedative effects. A low response rate by both subgroups after a lower dose of both drugs and in nondrug tests indicated that both drug effects were distinctively different from the nondrug condition.