Effects of intra-dentate gyrus microinjection of myokine irisin on long-term potentiation in male rats

Induction of long-term potentiation (IP) increases the storage capacity of synapses in the hippocampal dentate gyrus (DG). Irisin is a myokine generated from FNDC5 (a gene precursor) during exercise. Although intra-cornu am monis 1 administration of irisin fortifies LIP in mice with Alzheimer's disease, the effects of intra-DG injection of irisin on the LIP in rats remains to be elucidated in vivo. In this study, male Wistar rats were randomly divided into a control group (saline), irisin (0.5,1, and 1.5 mu g/rat), and dimethyl sulfoxide (DMSO). After treatment, the population spike (PS) amplitude and slope of excitatory postsynaptic potentials (EPSP) were measured in the DG of rats in vivo. Moreover, following completion of the experiments, the stimulating and recording sites in the hippocampus were confirmed histologically from brain sections. Furthermore, biochemical assays like malondialdehyde (MDA), total antioxidant capacity (TAO), and total oxidant status (TOS) were evaluated (the antioxidant markers were analyzed in the plasma). Our results suggest that all doses of irisin (0.5, 1, 1.5 mu g/rat) caused an increase in the EPSP slope and PS amplitude when compared with the control group. In addition, the results obtained showed that irisin decreased TOS and MDA levels while increasing TAC levels as a marker of lipid peroxidation in plasma. The present report provides direct evidence that irisin affects the activity-dependent synaptic plasticity in the dentate gyrus.