Expression of nNOS in the human larynx.

Although intrinsic laryngeal neurons and ganglia have been studied in various species, they have been overlooked in humans. We aimed to investigate the presence of intrinsic laryngeal neurons in humans and, if present, to analyze their neuronal nitric oxide synthase (nNOS) expression. An immunohistochemical study using anti-nNOS antibodies was performed on samples obtained from four cadavers. Intrinsic laryngeal nNOS+ neurons were assessed in the submucosal layer, but nNOS+ nerves were found in all histological layers of the larynx. nNOS expression was also found in striated muscle fibers of larynx. This might reveal the anatomical basis of an upwards extension of the nonadrenergic noncholinergic system in human airways, but further experiments are needed to assess an exact role of NO influence on neural transmission and muscular functions of human larynx.