大鼠胸段脊髓损伤后后肢神经肌肉的自然变化

A study of natural change of the nerves and muscles of hind limb in thoracic spinal cord injury rats

中文关键词:  脊髓损伤  自然变化  运动终板  透射电镜  运动单位计数  大鼠

英文关键词:Spinal cord injury  Natural change  Motor endplate  Transmission electron microscope  Motor unit number estimation  Rat

中文摘要:

  【摘要】 目的：观察大鼠完全性脊髓损伤后损伤平面以下周围神经和骨骼肌的自然变化，为脊髓损伤治疗与康复相关基础研究提供科学依据。方法：将50只健康成年雌性SD大鼠随机分为对照组（A组）5只、假手术组（B组）10只和脊髓损伤组（C组）35只，B组行单纯椎板切除术；C组在椎板切除基础上用横断法制成T10完全脊髓损伤模型。分别对3组大鼠术前，B组术后1、2周，C组术后1、2、4、12、24周进行BBB评分，并检测腓肠肌的运动单位计数（motor unit number estimation，MUNE）；再于各时间点处死大鼠，取坐骨神经和腓肠肌内侧头，应用光镜和透射电镜观察坐骨神经-运动终板-腓肠肌的形态变化。对3组所有结果进行对比分析。结果：C组术后各时间点的BBB评分与术前及A组、B组比较差异均有统计学意义（P＜0.05），C组术后4周时的BBB评分与其他时间点比较差异均有统计学意义（P＜0.05）。C组术前MUNE数值与A组、B组比较差异无统计学意义（P＞0.05）；C组术后各时间点与术前比较差异均有统计学意义（P＜0.05），术后4周与24周比较差异无统计学意义，其余各时间点比较差异均有统计学意义（P＜0.05）。A组和B组术后1、2周时坐骨神经有髓神经纤维髓鞘外形正常。C组术后1、2周时与A组、B组无明显差异；4周时部分有髓神经纤维髓鞘崩解、板层分离；12周时髓鞘崩解明显增多，高倍电镜观察见崩解的髓鞘板层清晰；24周时有髓神经纤维髓鞘崩解、融合，新生神经纤维管细壁薄，无髓神经纤维增多，高倍电镜观察见崩解的髓鞘板层模糊。A组肌细胞肌束膜及肌内膜边界清晰，肌细胞核位于肌膜下方。B组术后1、2周时与对照组无明显区别。C组术后1、2周时，除肌细胞截面积轻度缩小外，与对照组无明显不同；4周时肌细胞截面积缩小，局部肌细胞破坏；12周时多数肌细胞边界模糊，细胞核相对聚集，结缔组织增生明显；24周时肌细胞融合，细胞核密集，融合细胞间可见大小不一空隙，结缔组织增生更加明显。A组和B组术后1、2周运动终板结构清晰完整。C组术后1、2、4周时运动终板结构较A组、B组无明显差别；术后12周时相对完好运动终板与破坏运动终板并存，高倍电镜下观察见突触前膜、突触间隙、突触后膜层次分明，各层结构内可见细小颗粒，突触间隙内可见多个类圆形突触小泡，肌板清晰，同时也可见突触皱褶及突触前、后膜不可辨，肌板结构不清晰；术后24周时找不到运动终板。结论：大鼠完全横断性脊髓损伤后损伤平面以下周围神经和骨骼肌形态结构随时间退变程度逐步加重甚至消失；损伤后12周时已有明显变化，24周时出现显著的结构损害和功能丧失。

英文摘要:

  【Abstract】 Objectives: To investigate the natural change of peripheral nerves and skeletal muscles of hind limb after complete spinal cord injury(SCI) in rat models, and to provide scientific basis for the treatment and rehabilitation of spinal cord injury. Methods: Fifty healthy adult SD rats were randomly divided into control group(group A), laminectomy group(group B) and spinal cord injury group(group C). Complete SCI models were made by totally transecting the cord through laminectomy at T10 level in group C. For all groups, the sciatic nerve and gastrocnemius medialis were sampled for observation. Group A was sampled and observed one time, while for group B, pre-operation, 1 week and 2 weeks after operation were selected, and for group C, pre-operation, 1 week, 2 weeks, 4 weeks, 12 weeks and 24 weeks after SCI were selected. The study indexes included the nerve and muscle morphology, BBB score and motor unit number estimation(MUNE). Results: (1) After operation in group C, the BBB score at each observing time point was significantly lower than that of the group A and B(P<0.05), and partially increased at 4 weeks compared with other time points(P<0.05). (2)The MUNE values showed no difference between group C and group A at pre-operation(P＞0.05), between group C and group B at pre-operation (P＞0.05). The MUNE values showed significant differences between pre- and post-operation in group C(P<0.05), among all observing time points of post-operation(P<0.05) except for 4 weeks and 24 weeks. (3) In group C, 1 week and 2 weeks after operation showed no abnormal myelin axon morphology; at 4 weeks, part of myelin broke down, lamellar separated; at 12 weeks, myelin breakdown significantly increased, and lamellar of broken myelin was clear at the high magnification; at 24 weeks, myelin was in disintegration and fusion, regenerated myelin sheath was thin and unmyelinated nerve fibers increased, and lamellar of fragmented myelin was vague in the high magnification. (4)In group C, at 1 week and 2 weeks after operation, the muscle cell area appeared slightly smaller, yet no obvious difference with that of group A; at 4 weeks, the muscle cell area decreased, muscle cell boundary showed fuzzy; at 12 weeks, the hyperplasia of connective tissue was identified; at 24 weeks, muscle cell fusion and nuclear gathering appeared, while the connective tissue hyperplasia was obvious. (5)In group C, at 1 week, 2 weeks and 4 weeks after operation, the synaptic folds, pre- and post-synaptic membrane could be seen clearly with granular materials; at 12 weeks, relatively intact and destructive motor endplates coexisted. In the high magnification, synaptic folds, pre- and post-synaptic membrane was distinct, and messy synaptic folds, synaptic structure and uncontinuous Z line were also seen; at 24 weeks, the endplate structure could not be found. Conclusions: In transected SCI rats, morphological degeneration in peripheral nerves and skeletal muscles of hind limbs are gradually severe, which cause the collapse of the structure and complete loss of electrophysiological function at 24 weeks.