Immunohistochemical study on the distribution of neuronal nitric oxide synthase-immunoreactive neurons in the spinal cord of aged rat.

Despite in vivo studies suggesting an important function for nitric oxide (NO) in the spinal cord in the transmission of pain signals, sympathetic nerve activity and presumably other spinal functions, changes of neuronal NO synthase (nNOS)-containing neurons with aging in the spinal cord has not been investigated. In the present study, we demonstrated for the first time that the number of nNOS-immunoreactive neurons was significantly decreased in the central autonomic nucleus and the superficial dorsal horn of spinal cord in aged rats. Morphologically, the number and length of dendritic branches also seemed to be decreased. Combined with our previous studies, age-related decreases in the number of nNOS-immunoreactive neurons in the central autonomic nucleus and the superficial dorsal horn might be associated with the abnormality of micturition function or pain perception encountered in the elderly. However, the mechanisms underlying the decreased immunoreactivity for nNOS, and the functional implications require elucidation.