The machanism of delayed motor neuron death after transient spinal cord ischemia

迟发性截瘫是兔脊髓短暂缺血后8 ~ 24 h发生的一种独特现象。在胸腹部动脉瘤手术中短暂性主动脉闭塞后，也报告了这种类型的截瘫。因此，阐明延迟性截瘫的发病机制将为我们提供保护脊髓免受缺血性损伤的策略。本研究采用兔脊髓短暂性缺血（15 min）模型，探讨神经元死亡的主要类型，即凋亡和坏死，以及小胶质细胞和巨噬细胞的作用。评估后肢运动功能，并对腰髓进行形态学检查在再灌注后8、24或48 h进行HE和TUNEL染色以及生化检查（α-胞衬蛋白降解产物的测量和匀浆脊髓DNA变化的模式）。无运动神经元凋亡 ...更多信息 在任何动物身上都能找到。为明确小胶质细胞和巨噬细胞在延迟性截瘫发病中的作用，我们在形态学上研究了小胶质细胞、巨噬细胞和星形胶质细胞反应的时间过程（再灌注后2、4、8、12、24、48 h）。无论神经元损伤的严重程度如何，早在再灌注后两小时，小胶质细胞就开始在灰质的所有区域增殖。在严重神经元损伤的动物中，再灌注12 h后小胶质细胞反应继续增加，并开始观察到巨噬细胞。而在轻度神经元损伤的动物中，这种早期激活在24 h开始消退，直到再灌注后48 h才发现巨噬细胞。虽然再灌注后2小时也出现星形胶质细胞反应，但在严重神经元损伤的情况下，可观察到星形胶质细胞的肥大和增生.结果表明，迟发性截瘫与运动神经元的凋亡无关，而与坏死细胞的死亡有关.没有证据表明短暂缺血后小胶质细胞、巨噬细胞和星形胶质细胞的反应对运动神经元具有细胞毒性。这些胶质细胞和巨噬细胞似乎在防止缺血性损伤的扩展中起作用。少

Delayed onset paraplegia is a unique phenomenon that occurs 8 h to 24 h after transient spinal cord ischemia in rabbits. This type of paraplegia was also reported in humans after transient aortic occlusion in thoracoabdominal aneurysm surgery. Therefore, to elucidate the mechanism of delayed onset of paraplegia will give us the strategy to protect the spinal cord against ischemic injury. Using transient (15 min) spinal cord ischemia model in rabbits (15 min), we sought to determine which type of the neuronal death is predominant, apoptosis or necrosis, and to elucidate the role of microglia and macrophage.To examine the involvement of apoptosis in the delayed onset paraplegia, hindlimb motor function was assessed and the lumbar spinal cord was examined morphologically (HE and TUNEL staining) and biochemically (measurements of the breakdown products of α-fodrin and the patterns of DNA changes of the homogenated spinal cord) at 8, 24, or 48 h after reperfusion. No apoptotic motor neuron … More was found in any animals. There was neither detectable increase in a caspase-3-mediated breakdown product of α-fodrin nor DNA laddering in any animals.To clarify the role of microglia and macrophage in the delayed onset of paraplegia, the time course of the reactions of microglia, macrophage, and astrocyte was investigated morphologically (at, 2, 4, 8, 12, 24, 48 h after reperfusion). Microglia started to proliferate as early as two hours after reperfusion in all the area of the gray matter irrespective of the severity of neuronal injury. In the animals with severe neuronal injury, the microglial reaction continued to increase and macrophage started to be observed 12 h after reperfusion. Whereas in the animals with slight neuronal injury, this early activation began to subside at 24 h and no macrophage was found until 48 h after reperfusion. Although astroglial reaction also occurred as early as two hours after reperfusion, its hypertrophy and hyperplasia were observed in the case of severe neuronal injury.The results suggest that the delayed onset paraplegia is not associated with apoptotic motor neuron death but with necrotic cell death. There is no evidence that the reactions of microglia, macrophage, and astrocyte after transient ischemia is cytotoxic to motor neurons. These glial cells and macrophages appear to play a role in preventing the extension of ischemic damage. Less