Molecular Mechanism of Exercise Intensity on Neural Plasticity in Rats with Stroke

Abstract

Introduction: The goal of neuro-rehabilitation is to facilitate neural plasticity. Neural recoveries have been known to increase with exercise training, and effective exercise for recovery has been thought to be early, and mild-to- moderate intensity. However, evidence of mild-to-moderate exercise was mainly focused on hippocampal mRNA expressions previously. Furthermore, relation of exercise intensity to the neurotransmitters and molecules involved in nitric oxide synthase (NOS) pathway were not clearly manifested. Objectives: Aimed to investigate on the 1) changes in concentration of neurotransmitters during exercise, and 2) changes of neurotrophic, angiogenesis-related factors, and molecules associated with nitric oxide synthase pathway, which affect neural plasticity following different exercise durations and intensities after stroke in rats. Methods: The middle cerebral artery ischemia was induced in SD rats. One days following ischemia, treadmill training was performed for 30 minutes a i day. In experiment 1, rats were subjected to the control, 3-, 7-, 14-, and 28-day training group. In experiment 2, moderate (60 % of tolerable speed), and high (85% of the tolerable speed) intensity of treadmill trainings were done for 14 days. The Garcia test, and neurotransmitter sampling using the microdialysis were done in the last day of training. Concentrations of acetylcholine, serotonin, GABA, dopamine, and glutamates were quantified in the dialysates. The mRNA expressions of two immediate early genes (arc and c- fos), a neurotrophin (bdnf), and an angiogenesis-related factor (vegf) were measured using the RT-PCR. Proteins concerning NOS pathways (eNOS and nNOS), angiogenesis (VEGF), and long-term potentiation (NR2A/2B) were investigated in the Western blot. Immunofluorescence staining was done with antibodies to DAPI, GFAP, NeuN, nestin, and BrdU, and observed in the peri- infarct borderline zones. Results: Acetylcholine concentrations were raised in the 3-day exercise group, and then decreased in 14-day group. Glutamate concentrations were elevated in the 3-day training. The expression of bdnf mRNA was raised in day 14 with the increase of c-fos in the ischemic hemisphere. Levels of angiogenesis- related proteins such as eNOS, Akt, and VEGF were raised in day 14 in the contralateral hemisphere (Experiment 1). Following moderate-intensity trainings, NR 2A/2B ratios and VEGF levels increased in day 14. In contrast, high-intensity exercises induced increase of nNOS, in day 3 and 14, accompanied with elevated levels of immediate early genes (Experiment 2). BrdU+, nestin+ cells were observed 3 days following ischemia in the peri- infarct area. Conclusions: Moderate-intensity exercise for 2 weeks might be associated with neuroprotective mechanism such as neurotrophin, angiogenesis and LTP in rat stroke model. In contrast, high-intensity of training seemed to be associated with nNOS, a neurotoxic factor.