Decreased neuronal nitric oxide synthase expression and cell migration in the peri-infarction after focal cerebral ischemia in rats

Neuronal nitric oxide synthase (nNOS) regulates neurogenesis in the normal developing brain, but the role of nNOS in neurogenesis of the adult ischemic brain remains unclear. The aim of this study was to investigate the temporal and spatial relationship between cell migration from the ependymal/subventricular zone (SVZ) to periinfarction and nNOS expression in the rat. Ependymal/ subventricular zone cells were prelabeled with fluorescence dye DiI. Focal cerebral ischemia was induced by occlusion of the left middle cerebral artery. At 1, 3, 7, 14 and 21 days after ischemia, the rats were killed in order to determine the number of migrating cells, the colocalization of DiI and nNOS as well as nNOS quantity in specific regions. Compared to non-ischemic control and 1 day post-ischemia, the number of DiI-labeled cells in the selected regions increased at 3 days and peaked 14 days following ischemia. During 3-7 days post-ischemia, none of the migrating cells expressed nNOS and decreased nNOS expression was observed in the regions where migrating cells passed through. These results suggest the possible association between ependymal/SVZ cell migration and decreased nNOS expression within the areas including the migrating routes towards the peri-infarction.