A Comparative Study of Behavioral and immunohistological Changes after Spinal Cord Injury between Young and Adult Rats

Abstract

Purpose: The aim of this study was to compare the behavioral and immunohistochemical changes in a spinal cord injury (SCI) between young and adult rats and to clarify the differences in the mechanism underlying the changes in a SCI between young and adult rats. Materials and Methods: A total of 25 young and 25 adult male Sprague-Dawley rats (5 weeks and 16 weeks old) were used. The rats were anesthetized with pentobarbital and laminectomies were carried out at the level of the 11th and 12th thoracic vertebra. Using a modified New York University Impactor, a SCI was induced by dropping a 10 gm weight at a height of 20 mm. The bladders were emptied manually twice a day to prevent urinary problems. The animals that received no surgery were used as the normal controls. Behavior tests were performed using the Basso-Beatti-Bresnahan (BBB) scoring system, 1 and 7 days after the weight drop injury. The difference in the BBB score between the young and adult rats were analyzed by a paired t-test with a p value Results: The hind limbs of young rats were paralyzed 1 day after surgery, but had recovered partially 7 days after surgery. However, the adult rats remained in the paralyzed status 7 days after surgery. The c-Jun expression level increased in the gray matter up to 7 days after the weight-drop injury in adult rats. The c-Jun expression level increased significantly in the gray matter 1 day after the injury in the young rats. However, the c-Jun expression level decreased significantly in the gray matter 7 days after the injury in the young rats compared with that of the 1 day post-injury. The GFAP expression level in the gray matter increased 1 day after the weigh-drop injury in the adult rats. However, it decreased in the necrotic region 7 days after the injury in the adult rats. GFAP expression in the gray matter increased gradually up to 7 days after the injury in the young rats. Conclusion: These results suggest that lack of recovery from a SCI in adult rats may be related to the continuous upregulation of c-Jun expression and/or the downregulation of GFAP after the weight-drop injury. In contrast, the upregulation of GFAP expression and/or the downregulation of c-Jun expression in the spinal cord might be related to a partial recovery in young rats after a weight-drop injury.