Intravenous injection of neural progenitor cells improves cerebral ischemia-induced learning dysfunction

The ability of stem cells to enhance neurological recovery seen after cerebral ischemia has been reported. However, it remains to be clarified whether neural progenitor cells (NPCs) improve cerebral ischemia-induced learning dysfunction. We found in an earlier study that the direct injection of NPCs into the hippocampus prevents spatial learning dysfunction after cerebral ischemia. As the intravascular injection of cells represents a minimally invasive therapeutic approach, we sought to determine whether the intravenous injection of NPCs also would improve ischemia-induced spatial learning dysfunction. Cerebral ischemia was produced by the injection of 700 microspheres into the right hemisphere of rats. The injection of NPCs via a femoral vein on day 7 after the induction of ischemia improved the modified neurological severity score and reduced the prolongation of the escape latency seen in the water maze task on days 12-28 after cerebral ischemia. The intravenous injection of NPCs on day 7 did not affect the viable area of the ipsilateral hemisphere on day 28 compared with that of the non-treated ischemic rats. Furthermore, the NPCs injected via the vein were detected in the ipsilateral hemisphere; and they expressed brain-derived neurotrophic factor (BDNF) on day 28. The decrease in the BDNF level in the ipsilateral hemisphere was also inhibited by the injection of NPCs. These results suggest that the NPCs injected via the vein after cerebral ischemia improved spatial learning dysfunction, but without having any restorative effect on the damaged areas, possibly by acting as a source of neurotrophic factors.