Pulmonary Nociceptors are Potentially Connected with Neuroepithelial Bodies

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Abstract

Airway sensory receptors regulate cardiopulmonary function by providing constant information about the mechanical and chemical status of the lung to the central nervous system (CNS). There are at least three airway sensor types: slowly adapting receptors (SARs), rapidly adapting receptors (RARs), and C-fiber receptors (CFRs). We recently identified additional A-delta fiber receptors in intact rabbits that are different from SARs and RARs. Having a high mechanical threshold, they respond to hypertonic saline and are termed high threshold A-delta receptors (HTARs). SARs and RARs monitor airway mechanical changes, whereas HTARs and CFRs sense chemical alterations and may serve as nociceptors. As with nociceptors in other tissue, the latter are activated during lung inflammatory processes. Also, the airway houses neuroendocrine cells aggregated in organoids called neuroepithelial bodies (NEBs). NEBs are richly innervated by nerve fibers from different origins. Similar in structure to the carotid bodies, NEBs are believed to be sensors, with at least some sensory fibers that have cell bodies in the nodose ganglia. Therefore, they may serve CNS reflex functions. Strategically located at airway bifurcations, NEBs may signal the chemical composition of or presence of irritants in the air. This study intends to explore the possibility that NEBs are associated with nociceptors.