Influence of iNOS-induced apoptosis by mild hypothermia in the ischemic penumbra following bfocal cerebral ischemia-reperfusion in rats

Objective To explore the possible neuropmtective mechanisms of mild hypothermia by studying its effects on inducible nitric oxide synthase(iNOS)expression and apoptosis following focal cerebral ischemia-reperfusion in rats.Methods A total of 54 male Sprague-Dawley (SD)rats were randomly assigned to sham-operated group(Sham group),normothermia ischemia group (NT group)and mild hypothermia group(MH group).Ischemia/reperfusion models were induced by occlusion of the middle cerebral artery using the intraluminal suture method.At 48 h post-ischemia,the rats were anesthetized and their brains were removed.Adjacent sections were stained with hematoxylin and eosin(HE)for evaluation of iNOS protein expression and state of apoptosis in different cerebral regions.The dual immunohistochemical staining was performed to detect the relation between the iNOS protein expression and apoptosis,and measure the content of nitric oxide(NO).Results In the NT group,iNOS immunoreaction in ischemic penumbra(IP)of rat cortex was remarkably higher than that in the striatum and ischemic core of rat cortex;TUNEL-positive cells were also mainly localized in the cortical IP and the dual immunohistochemical staining detected expression of iNOS protein in TUNEL-positive cells.In the MH group,the expression of iNOS protein was significantly down-regulated in the IP and NO generation was reduced to suppress the number of apoptotic cells in the IP. Conclusion Mild hypothermia may exert its neuroprotective effects through inhibiting iNOS protein expression in the cortical IP and reducing NO generation to suppress apoptosis.