臂丛损伤后脊髓前角运动神经元超微结构改变

Ultrastructural changes of motor neurons in spinal cord following brachial plexus injury

目的探讨大鼠臂丛损伤导致脊髓前角运动神经元死亡的机制。方法成年雄性SD大鼠24只,其中对照组6只,损伤组18只。建立3种臂丛损伤模型:右C7前根撕脱(A组);右C7前根撕脱+同侧C5～T1后根离断(B组);右C7前根撕脱+右C5与C6之间脊髓半横断(C组)。术后14d取C7节段脊髓,采用尼氏染色方法和透射电镜技术,观察脊髓前角运动神经元的存活率及其超微结构改变。结果术后2周A组脊髓前角运动神经元的存活率最高,B组居中,C组最低。3个臂丛损伤组C7前角均可见凋亡特征性改变:运动神经元内核染色质聚集靠边,核固缩、碎裂、核膜皱褶并内陷,并有染色质团块形成的凋亡小体。细胞体积缩小,胞浆内细胞器密集,线粒体轻度肿胀,核周粗面内质网减少,游离核糖体增多,胞浆内可见较多的空泡。神经元胞体周围的有髓神经纤维和无髓神经纤维呈轻度肿胀,髓鞘的板层结构消失。结论臂丛损伤诱导脊髓运动神经元死亡途径中存在凋亡和坏死两种机制,运动神经元可形成凋亡小体。

Objective To investigate the mechanism of motor neurons death following the brachial plexus injury. Methods Adult male Sprague-Dawley rats were divided into control group and injury group randomly. The rats of the injury group were subdivided into three kinds of models of brachial plexus injury： right C7 anterior root avulsion （group A）, C7 anterior root avulsion with right C5-T1 posterior roots breaking （group B）, right C7 anterior root avulsion with hemi-transect between C5 and C6 segment of spinal cord （group C）. C7 spinal cord was harvested respectively at the 14th day after operation. Nissel method and transmission electron microscope technique was used to observe the livability and the ultrastructural changes of motor neuron in spinal cord. Results By two weeks after the brachial plexus injury, the livability of motor neuron was highest in group A, group B was between group A and group C. There were significant differences among three injury groups （P〈0.01）. The motor neurons of anterior horn exhibited features of apoptosis, including increased electron density in both of the cytoplasm and nucleus in intact cell and nuclear, the shrunken nucleus, and the reduced soma size of the cell. Occasionally, apoptotic bodies were found in these cells. Moreover, that rough endoplasmic reticulum reduced and free ribosome increased could be observed in the motor neurons. The lamellar structure of myelin sheath was disappeared and became vacuolar. Conclusion Motor neurons death following brachial plexus injury is thought under two major forms： necrosis and apoptosis. Apoptosis body is found in motor neurons.