Low-speed treadmill running exercise improves memory function after transient middle cerebral artery occlusion in rats

Physical exercise may enhance the recovery of impaired memory function in stroke rats. However the appropriate conditions of exercise and the mechanisms underlying these beneficial effects are not yet known. Therefore, the purpose of this study was to investigate the effect exercise intensity on memory function after cerebral infarction in rats. The animals were subjected to middle cerebral artery occlusion (MCAO) for 90 min to induce stroke and were randomly assigned to four groups; Low-Ex, High-Ex, Non-Ex and Sham. On the fourth day after surgery, rats in the Low-Ex and High-Ex groups were forced to exercise using a treadmill for 30 min every day for four weeks. Memory functions were examined during the last 5 days of the experiment (27–32 days after MCAO) by three types of tests: an object recognition test, an object location test and a passive avoidance test. After the final memory test, the infarct volume, number of neurons and microtubule-associated protein 2 (MAP2) immunoreactivity in the hippocampus were analyzed by histochemistry. Memory functions in the Low-Ex group were improved in all tests. In the High-Ex group, only the passive avoidance test improved, but not the object recognition or object location tests. Both the Low-Ex and High-Ex groups had reduced infarct volumes. Although the number of neurons in the hippocampal dentate gyrus of the Low-Ex and High-Ex groups was increased, the number for the Low-Ex group increased more than that for the High-Ex group. Moreover hippocampal MAP2 immunoreactivity in the High-Ex group was reduced compared to that in the Low-Ex group. These data suggest that the effects of exercise on memory impairment after cerebral infarction depend on exercise intensity.

► The effects of exercise on memory function after stroke depend on exercise intensity.
► Low-intensity exercise could improve some types of memory impairment.
► High-intensity exercise improved memory based only on negative reinforcement.
► Both low- and high-intensity exercise reduced the infarct volume.
► Low-intensity exercise promoted hippocampal plasticity linked to memory function.