Origin and distribution of NADPH diaphorase-positive nerves in rat nasal mucosa

The aim of this study was to localize the distribution of (reduced) nicotinamide-adenine dinucleotide phosphate (NADPH) diaphorase-positive nerves in the rat nasal mucosa by NADPH diaphorase histochemistry, and to determine its origin by utilizing retrograde tracing with Fluoro-Gold (FG). Fine varicosities of NADPH diaphorase-positive nerve fibers were distributed around blood vessels (arterioles in particular), submucosal glands, and the subepithelial layer of the nasal mucosa. Most of the ganglion cells and nerve fibers in the sphenopalatine ganglion, and a few ganglion cells in the trigeminal ganglion, were stained by NADPH diaphorase, but no NADPH diaphorase-positive ganglion cells were found in the superior cervical ganglion. Retrograde tracing with FG and co-localization of NADPH diaphorase demonstrated that the FG-labeled ganglion cells in the sphenopalatine ganglion were NADPH diaphorase-positive, but the FG-labeled ganglion cells in both the trigeminal and the superior cervical ganglia were NADPH diaphorase-negative. In conclusion, NADPH diaphorase-positive nerves distribute around blood vessels, around submucosal glands, and in the subepithelial layer of the rat nasal mucosa, and their origin is the sphenopalatine ganglion. These findings imply that nitric oxide may be co-localized to the cholinergic innervation and be involved in vasomotor and secretomotor control of the nasal mucosa.