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BACKGROUND: The application of exogenous antioxidant is always the focus in the prevention and treatment of cerebral ischemia. Phycocyanin has the effects against oxidation and inflammation, but its role in the pathophysiological process of cerebral ischemia reperfusion injury still needs further investigation.OBJECTIVE: To observe the effects of phycocyanin on the expression of superoxide dismutase (SOD),apoptosis and form of the nerve cells in rats after cerebral ischemia reperfusion injury.DESIGN: A randomized control animal experiment.SETTING: Institute of Cerebrovascular Disease, Medical School Hospital of Qingdao University.MATERIALS: Fifty-two healthy adult male Wistar rats of clean degree, weighing 220-260 g, were used. Phycocyanin was provided by the Institute of Oceanology, Chinese Academy of Sciences.METHODS: The experiments were carried out in Shangdong Key Laboratory for Prevention and Treatment of Brain Diseases from May to December 2005. ① All the rats were divided into three groups according to the method of random number table: sham-operated group (n=4), control group (n=24) and treatment group (n=24). Models of middle cerebral artery occlusion/reperfusion (MCAO/R) were established by the introduction of thread through extal and intal carotid arteries in the control group and treatment group. After 1-hour ischemia and 2-hour reperfusion, rats in the treatment group were administrated with gastric perfusion of phycocyanin suspension (0.1 mg/g), and those in the control group were given saline of the same volume, and no treatment was given to the rats in the sham-operated group. ②The samples were removed and observed at ischemia for 1 hour and reperfusion for 6 and 12 hours and 1, 3, 7 and 14 days respectively in the control group and treatment group, 4 rats for each time point, and those were removed at 1 day postoperatively in the sham-operated group. Forms of the nerve cells were observed with toluidine blue staining. Apoptosis after cerebral ischemia reperfusion was detected with TUNEL technique. SOD expression was detected with immunohistochemical technique. ③ The intergroup difference was compared with the t test.MAIN OUTCOME MEASURES: The apoptosis of the nerve cells and SOD expression were mainly observed in each group.RESULTS: Finally, 52 rats were involved in the analysis of results. ① Number of apoptotic cells: In the sham-operated group, a few apoptotic cells could be observed in brain tissue. The apoptotic cells at each time point in the control group and treatment group were obviously more than those in the sham-operated group (P ＜ 0.05). In the treatment group, the numbers of apoptotic cells at 12 hours, 1 and 3 days after reperfusion were significantly fewer than those in the control group, and those at 6 hours, 7 and 14 days were similar to those in the control group. ② Number of SOD positive cells: In the sham-operated group, there was weak expression of SOD in brain tissue, and the positive cells were extremely few, the positive cells at each time point were significantly more in the control group and treatment group than in the sham-operated group (P＜ 0.05). In the treatment group, the numbers of positive cells at 6 and 12 hours, 1 and 3 days after reperfusion were significantly fewer than those in the control group, and those at 7-14 days were similar to those in the control group. ③ Cellular forms: In the control group, the karyopyknosis occurred in the nerve cells,which were irregularly distributed, nucleolus disappeared, and some scattered cell fragments were observed.The forms of the nerve cells in the treatment group were generally normal.CONCLUSION: Phycocyanin plays a neuroprotective role in cerebral ischemia reperfusion injury by activating the SOD expression and inhibiting apoptosis.