Adaptation of guinea‐pig vagal airway afferent neurones to mechanical stimulation

Abstract

1 Intracellular and extracellular electrophysiological recording techniques were employed to examine the mechanisms involved in adaptation of guinea‐pig airway sensory neurones to suprathreshold mechanical stimulation in vitro. Extracellular recordings performed using an in vitro airway preparation revealed two unambiguously distinct subsets of mechanically sensitive nerve endings in the trachea/bronchus. In one group of fibres, the mechanical stimulus caused a brief burst of action potentials, after which the nerve rapidly adapted. In the other group of fibres, repetitive action potentials were evoked as long as the stimulus was maintained above threshold. 2 The adaptation response strictly correlated with ganglionic origin of the soma. Those fibres derived from the nodose ganglion adapted rapidly, whereas those derived from the jugular ganglion were slowly or non‐adapting. 3 Intracellular recordings from airway‐identified neurones in isolated intact ganglia revealed that the majority of neurones within either the nodose or jugular ganglion adapted rapidly to prolonged suprathreshold depolarizing current injections. 4 The electrophysiological adaptation of nodose ganglion‐derived neurones following prolonged suprathreshold current steps was greatly reduced by 4‐aminopyridine. However, 4‐aminopyridine did not affect the adaptation of rapidly adapting nodose ganglion‐derived nerve endings in response to mechanical stimuli. 5 The data suggest that ganglionic origin dictates adaptive characteristics of guinea‐pig tracheal and mainstem bronchial afferent neurones in response to mechanical stimulation. Also, the rapid adaptation of nodose nerve endings in the trachea observed during a mechanical stimulus does not appear to be related to the adaptation observed at the soma during prolonged suprathreshold depolarizing current injections.