NITRIC-OXIDE SYNTHASE IMMUNOREACTIVITY IN THE RAT, MOUSE, CAT AND SQUIRREL-MONKEY SPINAL-CORD

The distribution of nitric oxide synthase-immunoreactive neurons was e xamined in the spinal cord of rats, mice, cats and squirrel monkeys at the light microscopic level. Some sections were processed for choline acetyltransferase immunoreactivity. Double-labeling techniques were u sed to assess possible co-localization of nitric oxide synthase and ch oline acetyltransferase immunoreactivity in the same spinal neurons. N itric oxide synthase-immunoreactive neurons were concentrated in three fairly well-defined regions of the spinal cord of all species.studied : (i) the intermediolateral cell column of the thoracic and sacral seg ments, (ii) lamina X of all segments, and (iii) the superficial layers of the dorsal horn of all segments. A few nitric oxide synthase-immun oreactive neurons were scattered in the deeper laminae and the ventral horn. There were fewer nitric oxide synthase-positive neurons in monk ey spinal lamina X and dorsal horn than in similar locations of rodent s and felines. Double-staining showed that not all choline acetyltrans ferase-positive neurons in the intermediate cell column and lamina X w ere nitric oxide synthase-immunoreactive. In the ventral horn, choline acetyltransferase-positive neurons (presumed motoneurons) were nitric oxide synthase-negative. In addition to cell bodies, nitric oxide syn thase-positive fibers were scattered in the dorsal, lateral and ventra l horns of all species. Finally, punctate nitric oxide synthase-immuno reactive fibers were seen traversing the dorsal, lateral and ventral w hite matter, and reaching the respective gray matter. The present stud y shows that, in spite of quantitative differences, the pattern of dis tribution of nitric oxide synthase-positive neurons in the spinal cord was similar across the four species. The concentration of nitric oxid e synthase-positive neurons in the autonomic nuclei and laminae I, II and X of all four species underscores a prominent role of these neuron s in visceral and sensory functions.