| Objective: Cerebral vascular diseases (CVD) which are common in neurological diseases are divided into two parts: ischemic CVD and hemorrhagic CVD. According to domestic data, the percentage of cerebral infarction in CVD is 59.2%～85%. The ischemic injury is an important course of neurological deficit and the ischemic-reperfussion plays another important role in the pathophysiology of cerebral ischemic injury. When cerebral ischemic-reperfussion happened, the cellularenery metabolism disorder, free radical injury, the toxicity of excitatory amino acids, intracellular calcium overloaded and so on cause the aggravation of brain injury. Furthermore,the brain edema is one of the most evident histological changes after cerebral ischemic-reperfussion injury. Although lots of improve- ments have been made on the mechanism, prevention and treatment of brain edema, the treatment options are limited to osmotic agents such as mannitol, albumin and surgical decompression, and other maneuvers, none of which correct the molecular-level mechanisms responsible for brain edema. So the researches on this become the focus of clinical and primary studies. Aquaporins(AQPs)which called water channel protein, are related to water transport across membrane. The AQPs are expressed widely in the animal and plant kingdoms. AQP-4 that can only transport water is one of the most important AQPs expressed in the brain. AQP-4 is expressed in astroglia cells at the Blood Brain Barrier (BBB) and in ependyma and pial surfaces contacted with CSF. Many studies have testified that AQP-4 is closely associated with the onset and development of brain edema in cerebral diseases, such as cerebral ischemia,tumor,traumetic injury,inflammatory diseases and so on. But the relationship between AQP-4 and cerebral ischemic- reperfussion injury is poorly understood. The purposes of this study are to establish a reliable and reproducible animal model of brain ischemic-reperfussion, to observe the changes of behavioral function and brain water content, to confirm the AQP-4 expression and cell location in brain tissues and to analyze the relations among the neurological function, brain edema and AQP-4 expression on the basis of the brain ischemic-reperfussion rat model.Method: 60 adult male Sprague-Dawley rats were used in this study. The brain ischemic-reperfussion model was established by occluding middle cerebral arteries (MCA) with nylon sutures for three hours and then removed the sutures. The control group underwent the same operation as the model group except nylon suture insertion. At 6 h,24 h,48 h,72 h,7d after operation,all the rats were tested for neurological behavior using three different methods, including Longa Score, Berderson Score,Beam Walking Score. Then the rats were sacrificed, the brain tissues were quickly moved from the skull. The olfactory bulb and the frontal part (4 mm thick) was coronally cut and deserted. The frontal part (3 mm thick) of the other cerebrum was for brain water content measurement, which was calculated as the percentage changes between wet weight and dry weight using the following formula:(WW-DW)/ WW×100%.The postal parts were used for histological examination. This part of brain tissues was dealled after several procedures, including fixed in 4% formalin, dehydrated by different concentrations of ethanol and then embedded in paraffin. Then the brain tissues were cut into 5μm slices. Parts of slices were stained with hematoxylin and eosin to observe the inflammatory infiltration, the microgliocyte proliferation. Remained parts of slices were used to observe the AQP-4 expression using routine immunohistochemical methods. All the observations were done in both ipsilateral and contralateral of the ischemic region.Result: different neurological deficit was observed at different time points after brain ischemic-reperfussion. As the consequences of anesthesia and operation injury, the neurological deficits there were severe at 6 h, but there was no significant differences between two groups, P>0.05. During the 24 h to 72 h, there were significant differences between two groups, P<0. 05. At 7 d, the neurological function of the operation group almost recovered. At 6 h and 7 d, the brain water content of the ischemic-reperfussion and control group have no significant difference, P>0. 05. At 24 h (82.42±0.118),48 h (85.40±0.099) and 72 h (84.87±0.154), significant difference exsisted between two groups, P <0. 05,and the difference was highest at 48 h. Significant differences also exsisted between the ipsilateral and contralateral at 24 h,48 h and 72 h, P <0. 05. The HE stain of the model group indicated that around the ischemic region there were a few scattered neutrophils and the shape of neurons had no obverious changes at 6 h. At 48 h and 72 h, brain tissues around the ischemic focus were obviously swollen and necrotic, and there were a compact band of cells including inflammatory cells, cluster of intact erythrocytes and some cell debris. In the control group, there were no significant changes in the brain tissue. The immunohistochemistry stain indicated that there were up-regulated of AQP-4 expression in the brain tissues after brain ischemic-reperfussion compared with that of the control group. The expression of AQP-4 around the ischemic region gradually increased at 6 h (110.03±4.41) after cerebral ischemic-reperfussion, reached its peak at 48 h～72 h (116.06±9.53;126.18±2.64;140.06±1.19), and reduced but was slightly higher than control group at 7 d, P<0.05. The AQP-4 selectively expressed in the cell membrane of astrocytes and its foot processes adjacent to endothelial cells, and the positive stain was buffy, the positive cells were vacuolus. slightly stain was observed in the brain tissues of the control group and contralateral of the ischemic region. Conclusion: The model established in this study was reliable and reproducible. After cerebral ischemic-reperfusion, the changes of neurological behavior scores and the brain water content were consistent, which suggested that brain edema was the most important cause leading to neurological function deficit after cerebral ischemic-reperfusion. Moreover, the up -regulated of AQP-4 and the brain water content were also consistent in 72 h after operation; at 7 d, the brain edema resolved but the AQP-4 expression was also slightly higher than control group. This result suggested that the up-regulated of AQP-4 expression is closely associated with the occurrence and development of brain edema in the lateral period of cerebral ischemic- reperfusion, AQP-4 may play an important role in the clearance of the redundant brain water.
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