Intrahippocampal Injections of Ghrelin and Aerobic Physical Exercise: Effects on Learning and Passive Avoidance Memory in Rats

Ghrelin, an endogenous ligand for the growth hormone secretagogue receptors, plays a considerable role in important neurological effects related to food intake and energy homeostasis. As was found, regular physical activity may provide significant improvement of the cognitive functions in various behavioral situations. We aimed to evaluate the effects of ghrelin and physical training (aerobic exercises) on passive avoidance memory in rats. Experiments were performed on 64 three- to four-month-old rats. Experimental groups received intrahippocampal injections of 3.0 nmol ghrelin or/and performed aerobic exercises (running on a motorized treadmill) for 8 weeks. It was found that the combined influence of ghrelin and aerobic exercise significantly improves acquisition, consolidation, and retrieval of passive avoidance memory in rats, and the combined effects are considerably greater than the effects of separate applications of ghrelin and performance of exercise. It is supposed that aerobic exercise contributes to an increase in the endogenous production of ghrelin.