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

English Keywords:Spinal cord injury  Natural change  Motor endplate  Transmission electron microscope  Motor unit number estimation  Rat

English Abstract:

  【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.