Effects of Hippocampal Microinjection of Irisin, an Exercise-Induced Myokine, on Spatial and Passive Avoidance Learning and Memory in Male Rats

Abstract

Irisin is a soluble and exercise-induced myokine and/or adipokine hormone; generated by FNDC5 (a gene precursor) and also, it can ameliorate both motor performance and hippocampal neurogenesis. This study was designed to evaluate the effect of intra-dentate gyrus (DG) microinjection of irisin on both spatial and passive avoidance (PA) learning and memory in male rats. In this study, male Wistar rats were randomly divided into a control group (saline), irisin—receiving group (0.5, 1, and 1.5 μg/rat), and dimethyl sulfoxide-receiving group (DMSO) Morris Water Maze (MWM) and Shuttle Box (SB) tests were used to evaluate spatial and PA learning and memory, respectively. The results of MWM test showed that treatment with irisin (1 and 1.5 μg/rat) in day 3 and 4 of the training (acquisition) period caused a significant reduction in escape latency of rats in experimental group compared to control group. Subsequently, the results of probe-trial experiment in day 5 showed that treatment with irisin (1.5 μg/rat) enhanced formation of short-term memory compared to control group. In the retention trial, the results of SB test revealed that, all rats treated by irisin (0.5, 1, and 1.5 μg/rat) showed an increase in step-through latency (STLr) compared to control group (p < 0.05, p < 0.001, and p < 0.01, respectively). Also, the administration of irisin caused a decrease in the time spent in the dark box by rats. The results of the present study suggested that microinjection of irisin has led to the enhancement of both spatial and passive avoidance learning and memory. Further studies are needed to investigate how exactly the treatment with irisin influences memory and learning at the molecular level.