Afferent properties and reflex functions of bronchopulmonary C-fibers

Cough and ventilatory adjustments evoked by aerosolised capsaicin and distilled water (fog) in man

“…The C-fibre receptors have also been implicated (Lee and Pisarri, 2001;Widdicombe, 2001). Recently, a peculiar type of low-threshold mechanoreceptors has been described in the guinea pig extrapulmonary airways and has been suggested to be the actual cough receptor (Canning et al, 2004;Mazzone, 2005;Mazzone et al, 2005).…”

“…Recently, a peculiar type of low-threshold mechanoreceptors has been described in the guinea pig extrapulmonary airways and has been suggested to be the actual cough receptor (Canning et al, 2004;Mazzone, 2005;Mazzone et al, 2005). Although several in vivo experiments (Pisarri et al, 1991(Pisarri et al, , 1992Mohammed et al, 1993) indicate that in many animal species both the airway RARs and C-fibre receptors are activated by non-isosmolar solutions and capsaicin, a direct involvement of the latter sensor type in cough mediation is controversial (e.g., Widdicombe, 2001;Lee and Pisarri, 2001). Indeed, recent lines of evidence suggest a modifying and amplifying role for capsaicin-sensitive nerves in cough and other defensive reflexes in awake animals (Canning et al, 2006).…”

“…One type is characterised as rapidly adapting receptors (RARs), with prominent mechanical and less pronounced chemical sensitivity; their role in cough mediation is widely recognised (Widdicombe, 2001). The other type is represented by the sensory endings of the non-myelinated C-fibres (C-fibre receptors); they have little mechanical sensitivity but are exquisitely responsive to endogenous and exogenous chemicals (Lee and Pisarri, 2001). The role of these sensory endings in cough mediation is still object of * Corresponding author.…”

“…Whilst the ventilatory response evoked by RAR activation mainly consists of hyperpnoea, i.e., an increase in tidal volume without consistent changes in respiratory rate (Coleridge and Coleridge, 1986;Yu et al, 1998;Sant'Ambrogio and Widdicombe, 2001), stimulation of C-fibre receptors causes rapid shallow breathing, i.e., an increase in respiratory rate associated with a reduction in the depth of breathing (Lee and Pisarri, 2001). We have recently shown that, in humans, coughing induced by fog inhalation is preceded by increases in respiratory drive and minute ventilation by way of selective increases in the volume component of the breathing pattern (Lavorini et al, 2001), pointing at the possibility that the sensors primarily stimulated were the RARs.…”

Is TRPV1 a useful target in respiratory diseases?

“…The afferent activity arising from C-fiber endings plays an important role in regulating respiratory functions under both normal and pathophysiologic conditions. Capsaicin, a pungent ingredient of chili peppers, is known to activate airway C-fibers, and this activation has long been associated with the initiation of several central reflexes, including increases in respiratory rate, parasympathetic bronchoconstriction, mucus hypersecretion, vasodilation, as well as urge to cough sensations and sensations of dyspnea [2,3].…”