Effects of intracerebroventricular injection of different doses of insulin on spatial memory in healthy male Wistar rats

As one of the best known protein hormones, insulin has been recognized to play key roles in a variety of important biological process. Insulin acts on peripheral target tissues such as the adipocyte, muscle and liver to regulate glucose homeostasis. In addition to its peripheral functions, insulin and its receptor have been detected in central nervous system (CNS). Some of its effects on cognitive behaviors especially on learning and memory have been reported. Sixty male Wistar rats were divided into 6 groups randomly (n=10). All groups underwent a stereotaxic surgery and a canula was implanted in their third ventricle. Saline and different doses of Insulin (, 4,8,16 and 32 mU) were injected intracerebroventricularly. Behavioral tests carried out in Morris water maze 30 min and 24 h after injections. Our results demonstrated that the low and intermediate doses of insulin (2, 4, 8, 16 mU) showed no significant differences in escape latency and distance traveled to find hidden platform, while higher dose (32 mU) decreased these two parameters significantly. In the probe trial also those groups that received higher doses of insulin (16, 32 mu) spent more time in the target quadrant comparing with sham group. The present study suggests that intracerebroventricular administration of insulin affect memory dose dependently and higher doses improve spatial learning and memory.