Anatomical and immunohistochemical considerations on the microinnervation of trachea in humans

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.

Intrinsic neuroendocrine cells in the outer wall of the human pyriform recess

The extrinsic neural supply of the hypopharynx is well established. However, little is known about the intrinsic neurons and neuroendocrine cells (NECs) of the human hypopharynx that are under the influence of the extrinsic nerves. We aimed to identify and characterize such cell populations within the outer wall of the pyriform recess. We applied antibodies for neuron-specific enolase (NSE), calretinin (CR) and neurofilaments (NF) to autopsy samples from four donor cadavers. Within the lamina propria and the muscle layer of the pyriform recess outer wall, usually in perivascular areas, we found NSE-, CR- and NF-positive cells, mostly apolar, that were considered on a histological and immunohistochemical basis to be NECs. Although these cells have not, to our knowledge, been described previously in this anatomical location, their presence within the hypopharynx wall may explain the appearance of rare forms of local primary neuroendocrine carcinomas.

Tracheal telocytes

Recently, a novel type of stromal cell – the telocytes (TC) – was identified in mouse trachea. These cells are known to possess the ultrastructural characteristics, which support their role in intercellular signaling. We found TC in all stromal compartments of the tracheal wall. TC with long prolongations (telopodes, Tp) were lining longitudinally the collagen bundles, and were serially arranged (end-to-end connections of Tp were found). Noteworthy, Tp frequently establish stromal synapses with mast cells (MC). Primary cilia were also identified in TC. In conclusion, tracheal TC could be involved in the tracheal regulation (e.g. secretion, contractility). The tandem TC-MC deserves further investigations.