Some effects of scopolamine on a passive avoidance response in rats

Summary Results are reported for the effects of scopolamine and methscopolamine on a passive avoidance response in rats. Scopolamine in adequate doses severely disrupted both the acquisition and the retention of this response. Since methscopolamine was without effect, it was concluded that the site of action is in the central nervous system.It was found that the retention deficit cannot be attributed to dissociation and, surprisingly, that rats trained and injected with scopolamine on two consecutive days perform as well as normal controls on the second day. The possibility that this latter effect was due to tolerance found no experimental support.These results seem to suggest that scopolamine can produce response disinhibition. A neuronal hypothesis and a possible site of action for scopolamine were proposed to explain the behavioral data.This work was supported by Research Grant MH 08486-01 from the National Institute of Mental Health, United States Public Health Service. The author gratefully acknowledges the assistance of Allan Krebs who ran some of the animals in Experiments I and II and of Howard Moltz who made many helpful suggestions regarding a draft of this paper.