Detection of cholinergic mediation of behavior in 7-, 9-, and 12-day old rat pups.

A training procedure that permitted infant rats (7, 9, and 12 days old) to acquire a T maze discrimination to escape footshock (Experimental 1) was used to study the effects of the cholinergic antagonist, scopolamine hydrobromide (0, 0.2 mg/kg and 0.8 mg/kg) (Experiment 2). These results indicated that (1) Scopolamine had no effect on T maze choice behavior, unlike previous results for 15- and 23-day old rats, but (2) scopolamine did increase latency to choice in the discrimination task at all ages, an effect previously seen in 15-day old animals, but opposite that seen after scopolamine administration to 23-day old animals or adults. This "paradoxical" effect of scopolamine on response latency is present approximately two weeks prior to earlier estimates of the time course of maturation of the cholinergic system.