Objective      To study the time course of COX-2 mRNA and protein expression in rat cortex after global cerebral ischemia reperfusion insult.       Methods      The rat model of global cerebral ischemia reperfusion was established by bilateral common carotid arteries occlusion and systemic hypotension. Morris water maze was used to investigate spatial learning and memory function of the rats. Histological examination by HE staining was employed to examine the morphologic changes of rat cortex neurons. The SOD activity

and MDA content in rat cortex were evaluated by xanthinoxidase assay and TBA assay respectively. Expression of COX-2 mRNA and protein in the cortex was examined by reverse-transcription polymerase chain reaction (RT-PCR) and Western blotting

respectively.       Results      Compared with the sham group

all global cerebral ischemia rats showed significantly longer incubation period of seeking the platform

significantly less frequent cross-platform movement (

P

0.05) and shorter dwelling times in the platform quadrant (

P

0.01). Cortex neurons in the model group showed obvious karyopycnosis with remarkable cell loss and irregular cell contours. The SOD activity was obviously decreased and the MDA content was significantly increased in the global cerebral ischemia reperfusion group. The COX-2 mRNA and protein expression in rat cortex was remarkably increased in global cerebral ischemia reperfusion group. The COX-2 mRNA level reached the peak at 48 h (

P

0.05) after reperfusion and the protein reached the peak at 7 d (

P

0.01) after reperfusion.       Conclusion      Global cerebral ischemia reperfusion insults significantly increase the expression of COX-2 in rat cortex in a time-dependent manner.