Dictionary of Allergies .. Reflex bronchoconstriction

In addition to eliciting reflex bronchoconstriction via classic cholinergic pathways, it has recently been proposed that a reflex mechanism involving non adrenergic, non cholingeric (NANC) nerves may be activated via stimulation of non-myelinated C-fibre nerve endings which have been identified in human airways. Stimulation of these nerves may elicit an axon reflex involving antidromic conduction along afferent nerve collaterals, resulting in the release of neuropeptides such as substance P, neurokinin A, and calcitonin gene-related peptide (CGRP). These agents are potent inducers of bronchial smooth muscle contraction, bronchial oedema, plasma exudation and hypersecretion of mucus [1].

Sensory information in the lung is generated by airway receptors located throughout the respiratory tract. This information is mainly carried by the vagus nerves and yields multiple reflex responses in disease states (cough, bronchoconstriction and mucus secretion). Airway receptors are also essential for breathing control and lung defense. A single sensory unit contains homogeneous or heterogeneous types of receptors, providing varied and mixed behavior. Thus, the sensory units are not only transducers, but also processors that integrate information in different modes[2].

References

1. Barnes P.J.: Asthma as an axon reflex. Lancet 1:242-45. (1986).
2. Yu J. Airway receptors and their reflex function--invited article. Adv Exp Med Biol. 2009;648:411-20