| Objectives: To investigate the expression of MMP-9 and the cellular distribution of apoptosis after a spinal cord injury (SCI) model in rats and the effect of methylprednisolone on the expression of MMP-9 and cellular distribution of apoptosis so as to observe the effect of MMP-9 on neurocyte apoptosis after SCI. And then we can provide a theoretical base of molecular biology for the pathological process of insecondary-SCI and new idea of the treatment of insecondary-SCI. To investigate the effects and mechanism of MP on the nerve cell apoptosis after SCI so as to provide new theoretical base of SCI therapy by MP.Methods: 126 adult male SD rats (the weight is between 350 and 400 gram) were divided randomly into 3 groups: sham operation group, Allen's weight drop injury group and spinal cord injury with high does methylprednisone group. The first one was composed of 42 rats and the last two groups were both 42 rats too. Three groups were divided into the designated subgroups, i.e. 1h,6h,12h,1d,3d,5d and 7d after injury. And each subgroup contains 6 rats. In sham operation group, just the vertebral plate was removed after anesthesia. Building acute spinal cord injury model in rats with modified Allen's method by a 10g×5cm impact on the posterior T9-10 spinal cord in the SCI group. In MP group, the same model was made. By the standard of 30mg/kg, methylprednisolone was injected through caudal vein 30min after injury and the rats in SCI group were just injected the same amount of normal sodium. Rats were sacrificed at 1h,6h,12h,1d,3d,5d and 7d after injury. Five segments of each spinal cord were cut for morphological studies, including hematoxylin and eosin staining (HE), immunohisto chemical stainin and the terminal deoxy nucleotidy transferase-mediated deoxy-uridine triphosphate nick end labeling (TUNEL) methods. We used the SPSS 11.5 to process data and analyze the correlation of MMP-9 and apoptotic index.Results:①Immunohistochemistry staining: MMP-9 was negative in the sham operated group in the selective time. In the Acute Spinal Cord Injury group, the positive cells were noted primarily at the first hour, higher than before at sixth hour, achieved the maximum at the first day (the mean density was 0.310±0.019), could last for three days (the mean density was 0.261±0.024). Since then the positive cells reduced, but could be noted at the seventh day. The positive cells were expressed in the neurons which were ischemia, endothelial cells in vessel and the neutrophilic leukocytes. Compared to the sham operated group, the mean density was notable differences(P<0.05). In the MP group, the mean density of MMP-9 at the first hour was different obviously from other time points(p<0.05). However there was no difference between the 6h and 7d(P>0.05).② TUNEL staining: The positive cells weren't noted in the sham operated group. In the Acute Spinal Cord Injury group, the positive cells were noted primarily at the first hour, higher than before at sixth hour, achieved the maximum at the first day(the mean AI was 31.176±3.091), began to reduce at the fifth day, also could be noted at the seventh day. The positive cells were main in the neurons in the gray matter, but could be noted in the glial cells. The injury group compared to the sham group, the AI was notable differences(p<0.05). In the injury groups, the first day group compared to the other groups were notable differences, the sixth hour group compared to the seventh day group were different, but weren't notable. The positive cells were few in the group therapy, began to increase at sixth hour, achieved the maximum at the first day and could be lasted for(the mean AI was 21.928±2.141), began to reduce at the fifth day, also could be noted in seldom time. The MP group compared to the injury group were notable differences(p<0.05). In the MP group, the first day group compared to the other groups, the AI were notable differences(p<0.05,but the twelfth hour compared to the seventh day group weren't different.③Correlation about the mean density of MMP-9 and the mean AI of apoptotic cells: The expression of MMP-9 and the changes of AI were positive correlation(r=0.936, P<0.05).Conclusions:①The expression of MMP-9 in wounded spinal cord tissue was significantly higher after SCI model in rats, and reached a peak at the 24th hour, and descends gradually after the third day, and a few positive MMP-9 cells were still found in a week. The experimental results indicate that: the expression of MMP-9 after SCI may be relates to the pathological process of secondary spinal cord injury.②There is the nerve cell apoptosis in the wounded spinal cord tissue after SCI. After SCI, the apoptosis index gradually increased, and reached a peak at the 24th hour, and descends gradually after the third day, and a few positive apoptotic cells were still found in a week. The experimental results indicate that: there is the secondary apoptosis after SCI, and the secondary apoptosis result in further aggravated in primary spinal cord.③The express of MMP-9 after SCI was correlated with the secondary nerve cell apoptosis positively. The express of MMP-9 induced the secondary apoptosis of spinal cord cell, and be closely interrelated with the occurrence and development of the secondary spinal cord.④The methylprednisolone inhibited the expression of MMP-9 in the wounded spinal cord tissue after SCI, thereby it would ameliorate the degree of secondary spinal cord injury in rats.
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