Regulation of common carotid arterial blood flow by nitrergic neurons in the medulla of cats

Glutamate stimulation of the dorsal facial area, an area located dorsal to the facial nucleus, increases common carotid arterial blood flow. Nitrergic neurons are important in cardiovascular regulatory areas. We investigated whether the nitrergic neurons might be present and play a role in the dorsal facial area to regulate the arterial blood flow. Injections of l-arginine (an NO precursor) and sodium nitroprusside (an NO donor) into the area caused dose-dependent increases in the arterial blood flow. Injection of NG-nitro-arginine methyl ester (l-NAME, an NO synthase inhibitor) or methylene blue (a guanylate cyclase inhibitor) decreased the arterial blood flow. Nitrergic neurons and fibers were found in the dorsal facial area by histochemical staining of nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase, a maker of NO synthase. In conclusion, nitrergic neurons are present in the dorsal facial area and appear to release NO tonically in stimulating the area to cause increase in common carotid arterial blood flow.