Effect of treadmill exercise on the BDNF-mediated pathway in the hippocampus of stressed rats

- Physical exercise has an antidepressant-like effect.
- Immobilization stress decreases the levels of BDNF and p-Trk, Akt, GSK-3β, and mTOR.
- This stress decreases the expression of synaptic proteins.
- Treadmill exercise increases these proteins levels with or without stress.
- Exercise may increase synaptic protein levels via activation of PI3K/mTOR signaling.

A growing body of evidence suggests that exercise enhances hippocampal plasticity and function through BDNF up-regulation, which is potentiated by antidepressant treatment. However, little is known about the molecular mechanisms mediating the effect of exercise. The present study investigated the effect of treadmill exercise on PI3K/Akt signaling, which mediates synaptic plasticity in the hippocampus of stressed rats. Rats were subjected to immobilization stress 2 h/day for 7 days. The rats were run on the treadmill at a speed of 15 m/min, 30 min/day, for 5 days. Western blotting was used to assess changes in the levels of phospho-tyr490-Trk receptor, phospho-ser473-Akt, phospho-ser9-GSK-3β, phospho-ser2448- mTOR, and phosphor-thr389-p70S6K, and in BDNF and various synaptic proteins. Immobilization stress significantly decreased BDNF expression and phosphorylation of Trk receptor, Akt, GSK-3β, mTOR, and p70S6K in the hippocampus of rats; furthermore, synaptophysin, PSD-95, neuroligin 1, and β-neurexin were decreased. Treadmill exercise significantly attenuated the decreased expression of these proteins. Moreover, exercise significantly increased PI3K/Akt signaling in the absence of immobilization stress. These results suggest that treadmill exercise reverses stress-induced changes in the rat hippocampus via an increase in PI3K/Akt signaling and may induce a functional reconnection of hippocampal synapses that mediate antidepressant actions.