| BackgroundSpinal cord ischemia-reperfusion injury (SCIRI) is one of the difficulties of neuroscience research. SCIRI refers to the phenomenon that obvious spinal cord dysfunction occurs when spinal cord gets blood reperfusion a certain time after ischemia. In some cases, even it resulted in the phenomenon of irreversible spinal cord delayed neuronal death. The main damage caused by spinal cord ischemia-reperfusion injury is secondary injury after reperfusion, which determined the prognosis of spinal cord ischemia-reperfusion injury. Therefore, protecting the spinal cord neurons to avoid spinal cord neurons lipid peroxidation or apoptosis is the key to the treatment of spinal cord ischemia and reperfusion injury.Despite many strategies have been developed to increase the ischemic tolerance of spinal cord and minimize the incidence of neurological complications, spinal cord ischemia occurred in the patients undergoing thoracic aorta or thoracoabdominal aorta aneurysm surgery. The quoted figure3%to18%was incidence of residual permanent injury (acute and/or delayed paraplegia) caused by the ischemic episode. Spinal cord ischemia/reperfusion (I/R) injury could also take place during spinal surgery of tumor, disc decompression and deformity. The social expense associated with the medical management and lost earnings of this disorder over the course of one’s life was significant.ObjectiveTo investigate the effect of dexmedetomidine on hind limb function, histopathology, Bcl-2, Bax, Caspase-3malondialdehyde (MDA), superoxide dismutase (SOD) following spinal cord ischemia-reperfusion injury in rabbits and the mechanism underlying its neuroprotective effects.MethodsSpinal cord ischemia-reperfusion injury and its change rule was directly related to the degree of spinal cord secondary injury degree and injury mechanism, and it had an important influence on the choice of animal models for the meaning of the results of the study. Many factors had yet to establish satisfactory to spinal cord ischemia injury model, the SCIRI model was various, including common abdominal aorta block and lumbar artery block method of spinal cord ischemia reperfusion model was established, but there was no uniform classification and grading, research and application of single SCIRI model, obviously cannot meet the needs of the clinical treatment. At present, the SCIRI research mainly in lumbar spinal cord as the research object, and tend to choose the rabbit as experiment object. Lumbar spinal cord blood supply mainly from kidney ventral aorta, abdominal aorta in rabbits and lumbar artery walls were relatively thick, inner diameter thick, not easy bleeding when free, direct branch of lumbar arteries of abdominal aorta, often with intravenous lines, and high blood pressure, blood vessel wall thin, easily injured, once the injured blood vessels, bleeding due to smaller retroperitoneal clearance was difficult, and different species of the rabbit lumbar artery anatomical differences, lumbar artery for more than3, the number of the lumbar artery branch, direction, and the diameter of the obvious variation may directly affect the stability of the model and the results of the study. In addition, because of the retroperitoneal space was small, for finding the lumbar artery ligation and all, especially under the branch and common iliac artery ligation on renal artery branch, operation difficulty was bigger, longer operation time, all this high selective segmental artery ligation operation method of operation. The animal experiment adopts improved Zivin legal system for spinal cord ischemia-reperfusion injury model. The specific steps were as follows:Heparin sodium (150u/kg) was administered intravenously and allowed to circulate for5minutes. During this interval, the abdomen was sterilely prepared and draped. A midline laparotomy was made and the viscera reflected to the right. After opening the retroperitoneum, the abdominal aorta and vena cava were collectively clamped with Satinsky clamps just distal to the left renal artery, and again proximal to the aortoiliac bifurcation. Each animal un-derwent40minutes of warm spinal cord ischemia, with the clamps removed just before closure. Abdominal cavity was washed with gentamicin80000units and metronidazole10ml and abdominal incision was layered suture if there was no ooze blood in the abdominal cavity after abdominal operation.Spinal cord ischemia reperfusion model was built by modified Zivin method. A total of24rabbits were randomly divided into three groups:(1) sham group (n=8): animals were underwent surgical procedure but not aorta occluded;(2)1/R group (n=8):abdominal aorta was occluded for40minutes, followed by reperfusion; and (3) dexmedetomidine group (n=8):dexmedetomidine was infused60minutes before abdominal aorta occlusion and was occluded for40minutes, followed by reperfusion. Neurological function was evaluated4h,12h,24h,48h after reperfusion and spinal cord segment (L2-5) was harvested for histopathological evaluation. DNA fragmentation was assessed by TUNEL method. The expression of Bcl-2, Bax and Caspase-3was detected by immunohistochemical analysis and western blot analysis. Malondialdehyde (MDA) and total superoxide dismutase (SOD) activity were also assayed by Elisa.ResultsAll experimental animals were to survive in test cycle (2days). The animal survival rate was100%.5cases had postoperative urine retention whose bladder function improved by conservative therapy (massage). Breathing, heart rate, blood pressure, body temperature and other vital signs were stable. No redness and purulent secretion was found in postoperative abdominal incision.1. Hindlimb function was recorded using the Tarlov Scoring System. All rabbits in I/R control group had some progressive, functional decline. Rabbits treated with ulinastatin (I/R+DEX) did not have the same progression or severity as I/R controls. A statistically significance was observed between ulinastatin treatment and I/R group at12to48hours (P<0.01).2. Group S, I/R group and DEX+I/R group48h after reperfusion of spinal cord tissue section HE staining, observed under optical microscope can be found:S groups showed structure of nerve cells in the normal form,more normal motor neuron number, clear outline, no scattered around nere cells vacuolation,cells into polygon,cytoplasm uniform red dye, in the austenite in granular distributed evenly. The wnucleolus is obvious. I/R group displayed that nerve cell structure was not clear. The normal motor neuron number was absolutely small. Nerve cells pyknosis, Austenite light, dye, vacuolization in cytoplasm, nuclear atrophy were seen. Nucleoli disappeared; Hemorrhage stove was visible in the organization of blood vessels and the essence. DEX+IR group displayed basic normal nerve cell morphological structure and mild edema. The number of normal cells was more than I/R group. The nerve cells have also been cytoplasm and nuclear quality fuzzy change and cavitation relatively was less than I/R group.No significant bleeding was seen. DEX+I/R group dexmedetomidine pretreatment group) spinal cord anterior horn motor neurons normal percentage of the I/R group, ischemia reperfusion group) increased significantly, the difference was statistically significant (P<0.05).3. TUNEL-positively staining cells were minimally detected in the sham group, whereas the I/R group showed a significant number of TUNEL-positively cells. Ulinastatin intervention significantly decreased the number of TUNEL-positively staining cells compared to the I/R group4. The number of the positive cells containing Bcl-2protein expression (brown stain) increased in the DEX+I/R group compared to I/R control group. The number of positive cells containing Bax and Caspase-3protein expression (brown stain) decreased in the DEX+I/R group compared to I/R control group. But no obvious changes were observed in the sham group with regard to Bax, Bcl-2and Caspase-3.5. Following ischemia-reperfusion injury, the SOD activity in the DEX+I/R group was elevated significantly compared with the I/R group, but MDA content in spinal cord tissue was decreased significantly compared with I/R group Conclusions1. It can be confirmed that dexmedetomidine can protect spinal cord neurons after spinal cord ischemia reperfusion injury by pathological changes.2. In the spinal cord ischemia reperfusion injury, dexmedetomidine can reduce neuronal apoptosis, thus protect the spinal cord by promoting the expression of Bcl-2and inhibiting the expression of Bax, Caspase-3.3. It was shown that dexmedetomidine had neuroprotection, which was associated with the inhibition of lipid peroxidation. |
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