Changes in secondary lesions to motor neurons caudal to the injury site of spinal cord in rats

Abstract

Objective To explore the changes in secondary lesions to motor neurons caudal to a damage site on the spinal cord of rats. Methods Forty female adult Sprague-Dawley rats were given incomplete spinal cord injuries (SCIs) at the T10 level using a modification of Allen's method. Locomotor function was evaluated using an inclined plane test, modified Tarlov scores and the Basso-Beattie-Bresnahan (BBB) scale before the operation and 1,2, 3,4 and 5 weeks post surgery. Histomorphological changes at T10 and L5 were observed under a light microscope.Results ①Morphology of the distal spinal cord: 1 week after SCI, neurites and Nissl bodies of the motor neurons had decreased. By the 2nd week the decrease had become more obvious. At the 3rd week after SCI, neurites and Nissl bodies had not decreased further, but neuron atrophy and apoptosis were found. At the 4th to the 5th week after SCI, neurites and Nissl bodies had increased significantly. ②Morphology of the damage site: At the 1 st week after SCI, hemorrhage and inflammation as well as nerve fiber necrosis were observed. By the 2nd week astrocytes had-increased and a few nerve fibers had grown at the damage site. At the 3rd week, regeneration of nerve fibers and astrocytes were found. At the 4th to the 5th week after SCI astrocytes and nerve fibers had not increased further. ③Locomotion function: The angles of the inclined plane test, Tarlov scores and BBB scores had decreased significantly at the 1st, 2nd, 3rd, 4th and 5th week post injury compared with those before the SCI. The values at the 2nd, 3rd, 4th and 5th week were all significantly better than those at the 1st week after SCI. There was an increasing trend in scores from the 3rd week to the 5th week, but without significant differences compared with the 2nd week after the operation. Conclusions Secondary degeneration and damage, including decreases in neurites and Nissl bodies, neuron atrophy and apoptosis may occur in the motor neurons distal to the damage site in the early stage after SCI. This correlates with changes in the pathology of local damage. Key words: Spinal cord injury; Motor neurons; Secondary lesions