Nitric oxide as a modulator of medullary pathways.

1. The present study has employed in vitro electrophysiology and chemical neuroanatomy to determine whether nitric oxide (NO) could be considered a modulator at neurons involved in medullary cardiovascular control pathways. 2. The NO donor diethylamine-NO caused concentration-related depolarizations of the rat isolated nodose ganglion preparation that were sensitive to blockade by inhibitors of soluble guanylate cyclase. 3. Incubation of rat medulla oblongata sections (50 microns) with a polyclonal antibody to NO synthase (NOS) revealed a topographic network of NOS-containing neurons. Specifically, NOS-positive neurons were found throughout the entire rostral-caudal axis of the nucleus tractus solitarius (NTS) and also in the area postrema, dorsal motor nucleus of the vagus, nucleus ambiguous, caudal and rostral ventrolateral medulla, nucleus gigantocellularis and lateral paragigantocellularis. 4. These data indicate that NO has functional actions on centrally projecting rat vagal afferent neurons that ultimately innervate the NTS. Furthermore, neurons that contain the enzyme NOS and that are, therefore, capable of using NO are localized in medullary nuclei concerned with both parasympathetic and sympathetic cardiovascular control pathways.