The Study On The Relationship Between SEP And Pathological Changes In Chronic Spinal Cord Injury Of Rats

Objective:Establishing a chronic spinal cord compression model by placing water absorbing volumetric expansion material in the spinal cord of the rats has been recognized, and it has been widely used in experimental research. This study was designed to explore the situations of spinal cord injury and pathophysiological changes after establishing the rat model.Method:96 healthy adult male SD(Sprague-Dawley) rats numbered sequentially were randomly divided into experimental group(n=48) and control group(I group, n=48) by random digits table. The C6 posterior vertebral laminas of the rats in the experimental group were resected to exposing the spinal cord. Water absorbing volumetric expansion material was placed in the cervical spinal canal of C5 segment from the defect and the wound was directly sewn, while the rats in the control group were only removing the cervical vertebral lamina of C6 segment. After successful establishment of the rat model, 1 day, 2 days, 3 days, 7 days, 10 days, 14 days, 21 days and 28 days, respectively recording the rat's BBB score, SEP signal characteristics and the pathological changes of spinal cord as A group, B group, C group, D group, E group, F group, G group, H group, and the control group was set to I group. The SEP signal curves were processed and analyzed to obtain the final data. HE staining was used to observe the pathological changes and ischemic conditions of the spinal cord. TUNEL method was used to detect the apoptosis of injured spinal cord tissues, and observing the time and space distribution of apoptotic cells. Finally, recording the expression of GFAP protein in the spinal cord tissue through immunohistochemistry method, and the statistical analysis was performed.Results:Hindlimb motor function Basso Beattie Bresnahan(BBB) scores of after 3 days of the model building were significantly worst than that of the 7 days group and the twenty-eighth days group(p<0.05). Signal latency and amplitude decreased were found in all the somatosensory evoked potential signals of the experimental group, especially in the group F. The shape of the SEP signal curve is gradually close to normal one as the compression time prolonged. The white matter loosen, the reticular pattern, demyelinating changes, and the edema of the nerve and glial cells were found in the compressive spinal cord under the microscope. All the experimental groups can see varying degrees of nerve cell number decrease, but also observed microglial cell proliferation and around the nerve cells. The microglial cell massively proliferation which around the decreased nerve cells were shown in all the experimental group. But in group F, there was a large amount of spinal cord tissue liquefaction, local visible hemorrhage and necrosis and the anterior horn motor neurons were significantly reduced, while no scar formation was found. It is shown that the number of apoptotic cells were partial correlated with the compression time by TUNEL staining. Immunohistochemical staining: The glial cells gradually proliferated, cytoplasm of astrocytes with more process of the cells were observed from group A to group G, while the expression of GFAP tended to be stable in group G and group H. Thus, it showed that a few astrocytes appeared in the injury region in the first day after surgery, and the number of GFAP-positive cells reached the peak in the 21 day after operation in the rat model of chronic cervical cord injury. At the same time visible scar formation formed and reactive astrocytes proliferation were the most obvious without significant increase. The number of GFAP-positive cells in the control group were were significantly different with the number of GFAP positive cells in experimental group A and B(p<0.05).Conclusion:Establishing a chronic spinal cord compression model by placing water absorbing volumetric expansion material in the spinal cord of the rats well simulates the clinical symptoms of chronic progressive spinal cord injury. The experimental results have proved the correlation between the number of apoptotic cells and the time of spinal cord compression. Progressive spinal cord injury occurred after animal model building, but the time of reaching peak is the 14 days after operation, and the astrocyte reactive proliferation is the most significant. Therefore, the model provides more theoretical basis for the further experimental study.