| Objective:There is a growing application of somatosensory evoked potentials(SEP) in the examination of acute spinal cord injury(SCI) and it has showed a great advantage over physical examination and imaging techniques. The study was designed to evaluate the validity and feasibility of somatosensory evoked potentials. In this experiment, SEP of the induced SCI models was studied to evaluate the ability of SEP to be used as a parameter of the spinal cord function and to indicate the severity of SCI. The aim of this research is to find the association between the results of SEP and the spinal cord function as well as the severity of SCI. And furthermore, to provide experimental evidence to the timing of decompression after a spinal cord injury.Method:In this study,40 mice with a body weight between 300 and 350g are divided into four groups in a random way. Several models have been designed to simulate human SCI. In the present study, the clip compression mice model were applied. It causes a ischemia lesion, which is common in human spinal cord injury. The mice were anesthetized with a mixture of Ketamine Hydrochloride and Xylazine by intrabdominal injection. The 1-3 thoracic lamina were removed in all mice, while the dura were left intact. The spinal cord was injured at T2 by an aneurysm clip with a power of a 40g weight which made a sudden impact on the surface of spinal cord. The compression time was set from 5 to 30 minutes. According to the time of compression, the animals were divided into 4 groups(control,5min, 15min,30min). Each group consisted of 10 mice. SEP was used to assess neurologic function of the spinal cord in this study. SEP were recorded by stimulating the posterior tibial nerve at the left ankle. A recording needle electrode were placed in the scalp between two ears. A reference needle electrode was inserted into the scalp of forehead. A ground electrode was placed into the right forelimb.In control group, the SEP was recorded before and after both anesthetization and operation. While in SCI groups, SEP was recorded at 5min,15min,30min, 60min,6 hours,24 hours,3 days,7 days after the aneurysm clip was removed and before spinal cord injury was induced. Latency and amplitude were measured for each wave. The latency of SEP was measured from the onset of the stimulus to the moment when the peak occurred. The amplitude of a positive peak was measured from the positive peak to the immediately preceding negative peak.Tarlov behavior score was measured before surgery and at 1,3,7 days after the aneurysm clip was removed.The effects of the SCI on the SEP were evaluated by the changes of latency and amplitude of peak. The data were analyzed by analysis of variance, t-test and linear correlation. P-value less than 0.05 was considered statistically significant.Result:A stable wave form of SEP was recorded before spinal cord injury was induced. Gradual decrease of both the peak latency and the peak amplitude was observed after induced spinal cord injury。In the control group, SEP stayed in a quite stable condition during the whole process of the experiment. In the 5min group, both amplitude and latency of the SEP showed an obvious recovery in 5 min after decompression, as time went by, the recovery was fast while it was more obviously showed in the latency. After 3 days, both latency and amplitude reached the level before SCI was induced. In the 15min group, as showed in the results, the decrease of amplitude and the increase of latency were more pronounced, and neither the amplitude nor the latency reached the level before SCI was induced until 7 days after the decompression. In the 30min group, the waves of SEP were totally undetectable immediately after severe spinal cord compression was given,60min after decompression, SEP was detected again; latency and amplitude failed to reach baseline levels 7 days after decompression. The data of latency and amplitude in each group were analyzed with analysis of variance by F-test. In control group, no statistically significant change of the latency or amplitude was detected. In SEP, the change of its amplitude is more obvious than the change of its latency.Tarlov motor scores in the control group were significantly better than those in the injury groups. As compression time increased, Tarlov motor scores tended to get lower. It was showed in the results that the severity of the damage is associated with how long the cord compression last. The 5min group got better neurologic recovery from SCI than the 30min group.Conclusion:The results of the experiment proved that there is a strong association between the change of SEP and spinal cord function。SEP can be applied to evaluate the neurologic function of SCI models as a method of great sensitivity. The latency and amplitude of SEP after spinal cord injury change in a certain way that shows coherence with the decompression time. The sensitivity is better in amplitude than in latency.The designed study indicates as following:Early decompression of the spinal cord may promote the recovery of neurologic function after SCI in experimental animals. The prognosis for neurologic recovery gets worse as the existence of spinal cord compression remains, and in agreement with behavioral tests which assessed the SCI. A relationship seems to be detected between the timing of decompression after spinal cord injury and the degree of neurologic recovery. Early decompression may be of great benefits for spinal cord injury according to the evidence provided by the study.Finally, as a noninvasive technique, SEP is of great value in monitoring spinal cord function。...
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