Effects Of Mild Hypothermia On The INOS Expression And Apoptosis Following Focal Cerebral Ischemia-reperfusion In Rats

Objective To explore the neuroprotective mechanism of mild hypothermia bystudying the effect of mild hypothermia on inducible nitric oxide synthase (iNOS)expression and apoptosis following focal cerebral ischemia-reperfusion in rats.Methods The middle cerebral artery (MCA) of Sprague-Dawley rat wasoccluded for 2 hours by using the intraluminal suture method and thenrecirculated. iNOS activities in the ischemic brain were measured at the differenttime after ischemia respectively, and the time course graph of iNOS expressionwas made. The rats were randomly assigned to sham-operated group (Sham),normthermic group (NT) and intraischemic hypothermia group (IH). Brains werecollected to measure different items at the time in accordance with iNOS activitypeak. The infarction volume and histological morphological damage wereinvestigated; iNOS proteins, iNOS activity, nitric oxide (NO) concent andapoptosis were measured in the different brain regions;The dual staining wasperformed to detect the relation between the iNOS expression and apoptosis.Results 1. iNOS activity peak at 48h postischemia in normthermic group. 2.The increase of iNOS activity and iNOS immunoreactivity were detected instriatum and cortex at 48h postischemia in normthermic group. iNOSimmunoreactivity in cortical penumbra was significantly higher than that in thestriatum and the cortical core. TUNEL-positive cells mostly localized in thecortical penumbra. Dual staining showed the expression of iNOS protein inTUNEL-positive cells. It implicated that iNOS expression has a correlation withapoptosis in region and cellular localization. 3. Mild hypothermia significantlyreduced the infarct volume and ameliorated the histopathological damage in brain.It mainly salvaged the part of cortical tissue. 4. Mild hypothermia reduced iNOSprotein expression in the different brain regions, especially in the corticalpenumbra, as well as suppressed iNOS activity and NO generation in the cortexand striatum. Furthermore, mild hypothermia decreased the number of apoptosis.Conclusion 1. In the late phase of cerebral ischemia-reperfusion, NO generatedby iNOS involved in the pathological process following cerebral ischemia-reperfusion. 2. It is in the ischemic penumbra that iNOS expression has amarked correlation with apoptosis in the region and cellular localization, as wellquantity. 3. Mild hypothermia has a positive neuroprotective effect. 4. It isassumed that the inhibition of iNOS expression and reduction of sequent NOproduction to suppress apoptosis may be one of the mechanism of hypothermicneuroprotection.