Histochemical and immunocytochemical study of nitrergic innervation in human nasal mucosa

Nitric oxide (NO) is a free radical gas that has been found to be produced in neuronal cells by the action of the enzyme brain nitric oxide synthase (bNOS). The aim of this study was to identify NO-containing nerve structures in the human nasal mucosa by localizing bNOS and to find out whether NO production is attached to the parasympathetic system. For this purpose, immunocytochemistry with antibodies to bNOS and neurofilament was performed. Additionally, nicotinamide-adenine dinucleotide phosphate diaphorase (NADPH-d), an enzyme that correlates with the localization of NO synthase, and acetylcholinesterase were visualized in a histochemical double staining technique on frozen sections. The NADPH-d and bNOS reactions were found in axons of nerve bundles and in subepithelial, glandular, and vascular nerve fibers. Arteries showed a distinctly developed nitric innervation, whereas no activity was found in nerve fibers supplying veins. A high coexistence of NADPH-d in parasympathetic nerves could be detected. These findings suggest that NO takes part in the nerve control functions of the human nasal mucosa.