Effects of physostigmine on operant serial discrimination/reversal learning in rats.

Two experiments examined the effects of physostigmine on acquisition and performance of operant serial reversals by rats. In Experiment 1, four groups of rats (n = 6/group) were injected with either vehicle or 0.03 mg/kg physostigmine five minutes prior to each session, or vehicle or 0.5 mg/kg physostigmine immediately after each session of a three-stimulus (bright, dim or flashing light) repeated discrimination/reversal procedure. Rats treated with physostigmine pre- or postsession learned significantly more reversals over 50 sessions than animals injected with vehicle. Experiment 2 used only two discriminative stimuli, a light and a 2,500 Hz tone. Following establishment of a stable daily reversal baseline, postsession injections of physostigmine significantly increased the number of trials to criterion on the next session compared to each subject's control baseline. Results are attributed to enhanced between-session transfer of previously learned discriminated instrumental responses by physostigmine-treated animals.