BACKGROUND: Mechanical injury can cause the changes of polygene expression spectrum in rat cerebral cortical nerve cells, and then result in the changes of intracellular protein expression. At present, dielectrophoresis is combined with mass spectrum technique to detect the expression of different proteins in rat cortex after brain injury, but the protein chip technique requires further investigation. OBJECTIVE: To analyze the differences of protein expression spectrum in rat cerebral cortex before and after closed traumatic brain injury using WCX-2 protein chip technique. DESIGN: A randomized controlled animal experiment.SETTING: Training Division of the Medical College of Chinese Peoples Armed Police Force. MATERIALS: Seventy-two male SD rats of clean degree, 350 - 450 g, were provided by the Experimental Animal Center, Academy of Military Medical Sciences of Chinese PLA. Urea, trifluoroacetic acid, CHAPS and Tris (Sigma, USA); WCX-2 (Ciphergen, USA). Ultra-high speed hypothermia centrifuger (Bechman, USA); Rotary tissue microtome (Keuca, Germany); Biochip processor and PBS II-C protein chip reader (Ciphergen, USA).METHODS: The experiments were carried out in the Institute of Molecular Pathology, Central Laboratory, and Department of Pathology, Medical College of Chinese Peoples Armed Police Force from June 2005 to March 2006.①Grouping and treatment: The experiments were completed in molecular pathological institute, central laboratory and pathological department.①The rats were randomly divided into control group (n =12) and brain injury group (n =60). Marmarous weight-dropping models were duplicated at different time points in the brain injury group. In the control group, the rats were only treated by incising the skin of head top, without fixing the stainless steel hitting backup plate at the vault of skull, and obtain brain cortex for pathological and protein chip research, and they were killed after 24 hours. The rats in the brain injury group were killed at 4, 8,12, 24 and 48 hours after model establishment.②Pathological observation: Longitudinal section was made on cerebral cortex, and sections of 5 u m were prepared, then stained with hematoxylin and eosin (HE).③Protein chip analysis: 100 mg cerebral cortex was collected from each rat, and the protein content in sample was detected with Bradford method, meanwhile, WCX-2 protein chip was used to analyze the protein spectrum. The data were automatically collected with Ciphergen proteinchip 3.0 software, and the results were analyzed using Biomarker Wizard software to compare the differences of protein spectrum in rat cortex between the groups.MAIN OUTCOME MEASURES: Results of the pathological observation of cerebral cortex and the protein spectrum analysis.RESULTS:①Pathological changes of cerebral cortex: In the control group, no necrosis and edema was observed. In the brain injury group, injures of different severity occurred at different time points; After4 hours, focal or scattered red nerve cells could be observed, the size of some cells was increased, cytoplasmwas lightly stained, and only nuclear fragments were seen; After 8 hours, the necrotic nerve cells wereincreased, and the number of nerve cells was reduced, astrocytes (neuronophagia) could be seen in partialcytoplasm; there was small vascular dilatation, and endothelial cell proliferation; interstitial edema, regionalrarefaction lightly stained. After 12-48 hours, the necrotic nerve cells were reduced, and astrocytesproliferated.②Results of protein spectrum analysis: The WCX-2 experiment found that the expressions of5 639, 3 212 and 7 536 u proteins in cerebral cortex changed after injury in the brain injury group. The peakintensity of 5 639 u protein in the brain injury group at 8 hours after injury was higher than that in the controlgroup (P＜0.05); The peak intensity of 3 212 u protein in the brain injury group at 48 hours after injury washigher than that in the control group (P＜0.05); The peak intensity of 7 536 u protein at 24 hours after injurywas higher than that in the control group (P＜0.05).CONCLUSION: Brain injury can cause the changes of protein expression spectrum in cerebral cortex, it is suggested that brain injury can induce the expression of protein.