Establishment Of A Rat Model Of Delayed Spinal Cord Paraplegia And Study Of Its Underlying Mechanisms

Objective:1. Imitate the influence of the surgical repair of thoracic and thoracoabdominal aortic aneurysms, on the blood supply for spinal cord, establish a model of delayed spinal cord paraplegia after the ischemia of spinal cord for rats which features close similarity to the real clinical environment, simple operation, high repeatability, high occurrence rate of delayed spinal cord paraplegia, low mortality and long survival time for laboratory animals, and discuss major risk factors which may lead to delayed spinal cord paraplegia.2. Observe the pathological change for the spinal cord of rats with delayed spinal cord paraplegia and discuss the possible pathogenetic mechanism of delayed spinal cord paraplegia.3. Based on the possible pathogenetic mechanism of the delayed spinal cord paraplegia proposed in this research, carry out corresponding treatment, observe the therapeutic effect, and confirm the hypothesis concerning the pathogenetic mechanism of delayed spinal cord paraplegia in this research.Methods:1. Select SD rats as the laboratory animal in this research. Imitate the surgical repair of thoracic and thoracoabdominal aortic aneurysms. After the thoracotomy, use a small aneurysm clip to block the descending aorta at the junction of the left subclavian artery and descending aorta so as to create ischemia of spinal cord at the lumbar segments. Divide the rats into different groups based on the body core temperature upon the blocking of descending aorta and the different time for blocking. Observe the occurrence rate of Delayed Spinal Cord Paraplegia, survival rate and survival time for the rats in different groups.2. Select the rats which underwent descending aorta blocking in the temperature of33.0±0.5degrees centigrade for40minutes and the rats which underwent sham operation as research object. Observe the testing result of the rats in terms of Nissl staining of spinal cord at the intumescentia lumbalis, double-labeled immunofluorescence, and REAL-TIME PCR,6hours,30hours and48hours after removing the block of descending aorta respectively.3. Select the rats which underwent descending aorta blocking in the temperature of33.0±0.5degrees centigrade for40minutes and the rats which underwent sham operation as research object. Divide the rats which underwent descending aorta blocking into normal saline group, minocycline30mg/kg group, and minocycline90mg/kg group based on whether minocycline is used as cytosatics for the microglia and the dose of minocycline used. Observe the occurrence rate of delayed spinal cord paraplegia, survival rate and survival time for the rats in different groups. Results:1. Among the rats which underwent descending aorta blocking in different groups, the occurrence rate of delayed spinal cord paraplegia is high for the rats which underwent descending aorta blocking in the temperature of33.0±0.5degrees centigrade for40minutes. Mortality does not increase with the rising occurrence rate of delayed spinal cord paraplegia. The survival time is at least7days. There is a time window of descending aorta blocking for delayed spinal cord paraplegia after surgery both in case of low temperature and normal temperature. The range of time window in the temperature of38.0±0.5degrees centigrade is from10.0min to11.5min. The range of time window in the temperature of33.0±0.5degrees centigrade is from18min to40min.2. After the descending aorta blocking in the temperature of33.0±0.5degrees centigrade for40minutes, observe the pathologic change of spinal cord at the intumescentia lumbalis. Nissl staining reveals that after removing the clip for6hours, the number of motor neuron of ventricornu at the intumescentia lumbalis does not have a significant difference compared with that in the sham operation group(P>0.05). However,30hours after removing the clip, the number of motor neuron of ventricornu begins to witness a decline. There was significant difference compared to the sham group (P<0.05). It experiences a continuous decline after removing the clip for48hours, and the vacuoles due to the necrosis of numerous motor neurons can be observed. The numbers of motor neurons were significantly decreased (P<0.05) between the sham group,6h group and30h group. Double-labeled immunofluorescence shows that Ibal, EL-1β and IL-6do not see a remarkable increase in expression after removing the clip for6hours compared with the sham operation group. However, after removing the clip for30hours, there is a significant increase (P<0.05) in express. IL-16and Ibal, IL-6and Ibal exhibit co-express in the ventral horns of spinal cord. The testing result of REAL-TIME PCR reveals that after removing the clip for30hours, the expression of IL-16and IL-6mRNA is significant higher (P<0.05) than that in the sham operation group and6h group.3. After removing the descending aorta blocking for one hour, the rats of the minocycline90mg/kg group outperform the rats of the normal saline group in terms of BBB grading for the motor function of lower limbs30hours,36hours,48hours,60hours and72hours after the operation. The difference is significant (P<0.05). The difference between the rats of the minocycline30mg/kg group and the normal saline group regarding the BBB grading330hours,36hours,48hours,60hours and72hours after the operation does not have any statistical significance(P>0.05).Conclusions:1. By blocking the descending aorta of SD rats in the temperature of 33±0.5degrees centigrade for40minutes, a model of Delayed Spinal Cord Paraplegia after ischemia of spinal cord can be established, which features high occurrence rate of delayed spinal cord paraplegia, low mortality and long survival time for laboratory animals, and close similarity to the surgical repair of thoracic and thoracoabdominal aortic aneurysms in the clinical environment. The blocking time and temperature for the descending aorta are two crucial factors which decide whether Delayed Spinal Cord Paraplegia may occur after the operation.2. After rewarming, the microglia is gradually activated. The activated microglia, along with the inflammatory factors, i.e. EL-1β and IL-6released by it, is probably one of the pathogenetic mechanisms for the Delayed Spinal Cord Paraplegia after the ischemia of spinal cord.3. The minocycline as the cytostatics for the microglia may to some extent prevent the occurrence of Delayed Spinal Cord Paraplegia after the ischemia of spinal cord.