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

迟发性截瘫是兔短暂性脊髓缺血后8 ~ 24小时发生的一种独特现象。这种类型的截瘫也有报道在人类胸腹动脉瘤手术后短暂性主动脉闭塞。因此，阐明延迟性截瘫发病机制将为脊髓缺血损伤的保护提供策略依据。利用兔短暂性（15 min）脊髓缺血模型（15 min），我们试图确定哪种类型的神经元死亡是主要的，细胞凋亡还是坏死，并阐明小胶质细胞和巨噬细胞的作用。为了研究细胞凋亡在迟发性截瘫中的作用，我们在再灌注后8、24、48小时评估后肢运动功能，并对腰椎进行形态学（HE和TUNEL染色）和生化（α-fodrin分解产物和匀浆脊髓DNA变化模式的测量）检查。未见运动神经元凋亡，其他动物均未见。在任何动物中，caspase-3介导的α-fodrin分解产物和DNA阶梯均未检测到增加。为了明确小胶质细胞和巨噬细胞在截瘫迟发性发病中的作用，形态学研究了小胶质细胞、巨噬细胞和星形胶质细胞在再灌注后2、4、8、12、24、48小时的反应时间过程。小胶质细胞早在再灌注后2小时就开始在灰质的所有区域增殖，而与神经元损伤的严重程度无关。在神经元严重损伤的动物中，小胶质细胞反应继续增强，再灌注12 h后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小时开始消退，直到再灌注后48小时才发现巨噬细胞。虽然星形胶质细胞反应也早在再灌注后2小时发生，但在严重的神经元损伤情况下观察到其肥大和增生。提示迟发性截瘫与凋亡性运动神经元死亡无关，而与坏死细胞死亡有关。没有证据表明小胶质细胞、巨噬细胞和星形胶质细胞在短暂缺血后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