Objective: To investigate the protective mechanism of mesenchymal stem cells (MSCs) on cerebral ischemia-reperfusion injury in rats.Methods: 192 SD rats were randomly divided into sham-operated group, operated group, control group and MSCs-treated group. Before the transplantation, MSCs were labeled by bromodeoxyuridine(BrdU). One day after the reperfusion, 1×106 MSCs were injected via ipsilateral internal carotid artery and the same dose of PBS were given to the control group. Rats cerebral ischemia-reper...