Some effects of CNS cholinergic neurons on memory.

The aim of this study is to observe the relationship between the impairment in passive avoidance task induced in rats by the i.p. administration of muscarinic antagonists, scopolamine and methyl-scopolamine, and the change in acetylcholine (ACh) output induced by these drugs. Initially we studied the effects of these drugs on the animals' performance of a step-through passive avoidance task. We then measured the change in ACh levels after administration of these drugs using an in vivo brain dialysis technique. Scopolamine was effective in impairing the performance of the passive avoidance task, while methyl-scopolamine did not have clear effects on the performance of the task. With regard to ACh output, scopolamine increased ACh dose-dependently and methyl-scopolamine also affected ACh release. These data suggest that the accumulation of ACh in the synaptic cleft may be involved in the memory deficit induced by scopolamine.