Increased expression of nitric oxide synthase in the gracile nucleus of aged rats.

Aging is associated with disturbances in autonomic cardiovascular control. The purpose of this study was to test the hypothesis that changes in nitric oxide occur with aging in brainstem nuclei involved in autonomic cardiovascular control. The principal and unexpected finding in this study was that NADPH-diaphorase reactivity, which is considered a marker of neuronal nitric oxide synthase activity, was decidedly increased in the neuronal bodies of the gracile nucleus but decreased in the axons and axon terminals in old compared with young rats. In situ hybridization also revealed that nitric oxide synthase gene expression was enhanced predominantly in the gracile nucleus neurons of aged rats. The differences between the young and old rats were most dramatically evident in the gracile nucleus, but not evident in other brainstem nuclei. The significance of this finding as it might relate to autonomic or other specific neural dysfunction with aging is not evident at this time.