An experimental study of the kinetics of neuronal nitric oxide synthase during the early phase of cerebral ischemia in focal cerebral ischemic rats *
Neuronal nitric oxide synthase (nNOS) is responsible for neurotoxicity during incipient cerebral ischemia. The objective of this study was to investigate the correlation between cerebral ischemic lesions and nNOS expression after middle cerebral artery occlusion (MCAO) in male Wistar rats weighing 200-250 g. MCAO was performed using the intraluminal suture method, and the rats were randomly assigned to a control group, and 1-hr., 2-hr., and 4-hr. MCAO groups. Ischemic areas were subdivided into two regions including the ischemic core and ischemic penumbra, respectively. After MCAO, nNOS and nNOS mRNA were determined by immunohistochemistry and in situ hybridization, respectively. The number of positive cells with nNOS mRNA in the ischemic hemisphere did not significantly increase following ischemic loading, being comparable to those in non-ischemic sites. In the ischemic core site, however, an increase in positive cells with nNOS itself was observed at and after 1-hr. of ischemia. In the peripheral areas. such an increase was observed at 4-hr. after ischemia and thereafter. In contrast, an increase in positive cells with caudate putamcn in the non-ischemic sites was observed at and after 2-hr. of ischemia. To ascertain nNOS enzymatic activity, plasma No2- and No3- (NOx) levels in the jugular vein of the ischemic side were measured. Plasma NOx levels significantly increased at and after 2-hr. of ischemia. However, this increase was inhibited by administration of 7-nitroindazole, a selective nNOS inhibitor. Based on these findings, it is conceivable that nNOS expression is stimulated by ischemia, with such a mechanism being predominantly regulated through its translation phase, rather than the process associated with mRNA. Areas with nNOS expression extended from the core site to the ischemic penumbra, with the lapse of time of ischemia, and resulted in expression even in a part of the non-ischemic hemisphere. Findings obtained by determination of NO metabolites indicate that nNOS might possess enzymatic activity. This is consistent with evidence that the neurotoxic activity of NO produced by mediation via nNOS extended from the core site to the ischemic penumbra with the lapse of time after ischemia. It was also found that local cerebral ischemia would have an influences on the non-ischemic hemisphere. (Accepted on September 3, 2001) Kawasaki Igakkaishi 27(3) : 209-218, 2001
