The effect of intracerebroventricular administration of insulin on memory impairment-induced by scopolamine in male rats

Introduction: Cholinergic neuronal deficiency is one of the main causes of Alzheimer's pathology, which leads to learning and memory impairment. Scopolamine is a muscarinic cholinergic antagonist commonly used to induce Alzheimer's disease (AD). Insulin also regulates learning and memory function. Thus, the aim of this study was to determine the effect of central administration of insulin on passive avoidance learning. Methods: In this experiment, fifty-nine rats were divided into 6 groups: (1) intact, (2) sham, (3) scopolamine-saline, (4) scopolamine-insulin4, (5) scopolamine-insulin8 and (6) scopolamine-insulin16. In addition, scopolamine (70nmol/2μl) was injected into the right lateral ventricle, before the retrieval test of the inhibitory avoidance task. Then the effects of three doses of insulin (4, 8 or 16 mU/2μl) were investigated on the passive avoidance learning in an amnestic model induced by scopolamine. Results: Our results indicate that the retrieval of passive avoidance memory was significantly improved by intracerebroventricular administration of insulin in 4 and 8 mU/2μl doses but not in 16 mU/2μl. Conclusion: These results confirmed that insulin could improve the retrieval phase of passive avoidance memory that was impaired by scopolamine.