Effect of cerebral administration of enalapril on spatial memory in scopolamine-induced amnesia in rats

  Numerous studies conducted in laboratory animals and humans indicate that angiotensin converting enzyme inhibitors reinforce memory and learning. In this paper we study the effect of injection of enalapril into the cerebral ventricles on spatial memory of white mice in the double- y maze, following the induction of an Alzheimer- like amnestic model with scopolamine. To estimate the duration of working memory, the adaptive response method was used following a temporal pause. Animals completing the training period were injected with 2.5 mg intraperitoneal scopolamine. Injection of this dose that was determined by the dose-response curve led to a significant decrease in the percentage of correct responses of working memory (p<0.01), without any effect on reference memory. Response delay time significantly increased in both types of memory (p<0.01). Therefore, an Alzheimer-like amnestic model was induced by this dose with a relatively isolated effect on current memory. Following induction of this amnestic model in mice, the effects of 3, 5 and 10 µg injections of enalapril on the percentage of correct responses and delay time were measured without pause and also by the adaptive response method with 5 and 30 second pauses. Enalapril led to an increase in correct responses of working memory in all doses without pause (p<0.01), while this effect was only observed at 3 and 10 µg doses of enalapril with pause (p<0.05). Enalapril led to a decrease in response delay in both types of memory (p<0.05). Considering these results and previous studies, it seems that enalapril blocks the inhibitory effect of endogenous angiotensin II on the cholinergic memory centers, and thereby leads to a reinforcement of memory, especially working memory.