Sensory nerves and airway inflammation: role of A delta and C-fibres.

It is generally accepted that stimulation of primary afferent sensory neurons, that innervate the airways, by chemical and mechanical stimuli leads to a range of homeostatic and defensive reflexes such as cough. However, there is still much debate regarding the exact type of sensory fibre involved in evoking these reflex events. The current dogma suggests that the major fibre types implicated in participating in reflex events of a protective nature are the A delta fibres and those stimulated in response to inflammation by noxious stimuli and mediators associated with tissue damage are the unmyelinated C-fibres. Furthermore, the C-fibre afferents are also believed to be responsible for mediating local axon reflexes, the release of neuropeptides and neurogenic inflammation. This review will concentrate on describing the characteristics of these sensory fibres and their proposed role in airway defensive reflexes and their possible exaggerated function in response to the inflammatory process.