This study examined the differences in NOS expression after a spinal cord injury (SCI) in young and adult rats.

20 Sprague-Dawley rats (5 weeks and 16 weeks) were anesthetized with halothane, and laminectomies were performed at the level of the eleventh thoracic vertebra. The spinal cord injury was induced using the dropping method. Immunohistochemistry for nNOS and iNOS and NADHP-d for eNOS were performed on the spinal cord after SCI 1 and 7 days after surgery. The behavior of the rats subjected to spinal cord injury were examined by BBB scoring. The differences between the young and adult rats were analyzed using a paired t-test with significance set at p<0.05.

There was a decrease in the number of nNOS immunoreactive cells, and an increase in the number of iNOS immunoreactive cells and NADPH-d positive (eNOS reactive) blood vessels in the spinal cords of the adult rats 1 and 7 days after SCI. On the other hand, in the young rats, the number of nNOS immunoreactive cells in the spinal cords was maintained 1 day after SCI, and NADPH-d positive (eNOS reactive) blood vessels were abundant in the spinal cords 1 and 7 days after SCI. There was a higher iNOS immunoreactivity in the spinal cords of the adult rats after SCI than in the young rats. The motor dysfunction of the hind limbs was slightly lower in the young rats was than in the adult rats. In addition, the recovery of the motor dysfunction was more rapid in the young rats than in the adult rats.

An increase in the neuroprotective eNOS reactivity was prominent in young rats, whereas an increase in neurodestructive iNOS expression was prominent in the adult rats.