Introduction: Cholinergic systems are involved in learning and memory. Scopolamine as muscarinic acetylcholine receptor antagonist, is used for creation of impairment in the memory. The purpose of this study are evaluation of effect scopolamine on avoidance memory and the effect of this phenomenon on the number of neurons in the hippocampal CA1 region of male Wistar rats. Material & Methods: in this study, Thirty-five male Wistar rats (20 ± 200 g) were divided randomly into five groups. Control group (Healthy samples) and 3 Experimental group with sham group (saline) were tested by the method of passive avoidance (shuttle box) in doses of 0.2, 0.5 and 1 mg/kg (intraperitoneally) as a single dose. After one week, from rats were taken memory of test. Finally, with dissection brains of rats and tissue operations and neurons stained with cresyl violet and photographs of the samples, neurons were counted in hippocampal CA1 region. Results: our results showed that injection of scopolamine after training to rats, caused memory Destruction compared with the group that had received saline. The number of neurons in the hippocampal CA1 region in response to scopolamine with dose 1 mg/kg (5/2 ± 27/97) showed a significant decrease to compared with controls (7/1 ± 31/87). This decrease was seen at other doses with lower difference. Conclusion: memory impairment-induced by scopolamine is probably associated with neuronal loss.

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