BACKGROUND:The majority of studies focus on the lesions of spinal cord injury, while little evidence is available on the change of morphology and structure of distal nerve, muscle and motor endplates fol owing spinal cord injury.
OBJECTIVE:To investigate the time window change of the morphology of motor neurons and skeletal muscles caudal to the lesion after spinal cord injury in rats.
METHODS:Fifty healthy adult Sprague-Dawley rats were randomly divided into three groups:control group (n=5;without treatment), sham operation group (n=10), and spinal cord injury group (n=35). The sham operated rats only received laminectomy. In the spinal cord injury group, rats were subject to complete T 10 spinal cord injury by total laminectomy and cord transverse resection. Then the morphological change including sciatic nerve, motor endplate and median gastrocnemius was observed for each group at 1, 2, 4, 12, 24 weeks after injury.
RESULTS AND CONCLUSION:(1) The myelin sheath layers of sciatic nerve were separated partial y at 4 weeks in rats with spinal cord injury, the myelin sheaths were fragmented with the regeneration of thin-myelinated and unmyelinated axons at 12 weeks. There was a decrease in myelinated axons and an increase in thin-myelinated and unmyelinated axons at 24 weeks. (2) The synaptic gutters of motor endplate, the presynaptic and postsynaptic membrane and synaptic space were distinct at 4 weeks in rats with spinal cord injury, the degenerated motor endplates coexsisted with the intact ones at 12 weeks. The motor endplate disappeared at 24 weeks. (3) There was a slight decrease in muscle cross-sectional area at 2 weeks in rats with spinal cord injury, but no structural change was found, the membrane of myocytes was partial y weakened at 4 weeks, the border of myocytes was obscure with hyperplasia of connective tissue at 12 weeks, and myocytes gathered and in fusion at 24 weeks. As natural history of completely transected spinal cord injury in rats, there were significant changes in morphology of peripheral nerve, motor endplate and skeletal muscles caudal to the lesion at 12 weeks, and the changes were destructive at 24 weeks.