RAT SPINAL-CORD NEURONS CONTAIN NITRIC-OXIDE SYNTHASE

We describe the distribution and characteristics of nitric oxide synth ase-containing neurons in rat spinal cord using a polyclonal affinity- purified antibody against rat cerebellar nitric oxide synthase. Numero us neurons were stained throughout the entire rostrocaudal extent of t he spinal cord. Cell bodies, dendrites and axons stained in a uniform manner. Nitric oxide synthase immunoreactivity was intense in neurons of laminae I-IV and X throughout the entire spinal cord. Neurons in th e intermediolateral cell column of the thoracic and lumbar spinal cord were also intensely stained for nitric oxide synthase. The sacral cor d demonstrated substantial nitric oxide synthase immunostaining within lamina VII. For the entire cord, scattered neurons in laminae V, VI, VII, and VIII were weakly positive. In addition, punctate nitric oxide synthase staining throughout laminae I, III and surrounding some larg e motor neurons in the ventral horn suggested the presence of nitric o xide synthase at synapses. Axons and dendritic terminals located in th e gray and white matter were also stained. The majority of nitric oxid e synthase positive neurons in the intermediolateral cell column were double-labelled by subcutaneously injected FluoroGold confirming that these cells were preganglionic autonomic neurons. Most NADPH-diaphoras e-stained neurons were also nitric oxide synthase-positive. The distri bution of nitric oxide synthase-containing neurons in spinal cord sugg ests that nitric oxide plays a role in spinal cord neurotransmission i ncluding: preganglionic sympathetic and parasympathetic, somatosensory , visceral sensory and possibly motor pathways. In particular, the aut onomic nervous system appears enriched with nitric oxide synthase immu noreactivity. The precise role of each neuron type remains to be demon strated in physiologic and pathophysiologic paradigms.