Effects of psychoactive drugs on short-term memory in rats and rhesus monkeys

To examine the effects of drugs on short-term memory in animals, the delayed discrimination experiment in rats and the delayed matching to sample experiment in rhesus monkeys were conducted. Nicotine at 0.125 mg/kg, s.c. in rats and at 0.5 mg/kg, s.c. in monkeys increased the percentages of correct choices. Scopolamine at 0.06-0.12 mg/kg, s.c. in rats and at 0.015 mg/kg, s.c. in monkeys decreased the percentages of correct choices. However, supposedly memory-specific, delaytime-dependent disruptive effects by scopolamine were found only in monkeys. Diazepam at 0.5-2 mg/kg, s.c. did not change the correct choices in rats. However, diazepam at 1-4 mg/kg, i.g. decreased the correct choices in monkeys regardless of the delay time. Chlorpromazine at 0.25-1.5 mg/kg, s.c. showed inconsistent effects in rats. In monkeys, chlorpromazine at 0.25-0.5 mg/kg, s.c. had no effect. These results suggested that using both rats and monkeys would be useful for evaluating the effects of drugs on memory.