Some effects of scopolamine on a passive avoidance response in rats

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.