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

Abstract

The sensory nerve fibres supplying the guinea-pig trachea and main-stem bronchi are mainly vagal fibres with somata located within the nodose and jugular ganglia (Kummer et al. 1992;Riccio et al. 1996b). While subpopulations of these nerve endings can be excited by chemical and non-isoosmotic stimuli, the majority of them respond to mechanical stimuli (Riccio et al. 1996a;Pedersen et al. 1998). Of the fibres that respond to a von Frey fibre mechanical stimulus, there are both low threshold and high threshold mechanoreceptors. Previous studies from our laboratory have shown that the low threshold mechanoreceptors originate from somata within the nodose ganglion and the high threshold mechanoreceptors originate from somata within the jugular ganglion (Riccio et al. 1996a). Two types of mechanoreceptors have been characterized based on their response pattern to the mechanical forces imposed upon lung inflation, namely slowly adapting receptors (SARs) and rapidly adapting receptors (RARs).RARs, which discharge during lung inflation and then become refractory during maintained inflation, were first discovered in the airways by Knowlton & Larrabee (1946). Later, Widdicombe (1954) described RARs as irritant receptors that were largely located in the conducting airways and SARs as stretch receptors located primarily within the lung. Although this dichotomy has been established for some time, relatively little is known regarding the mechanism of adaptation to mechanical stimuli. A central question regarding the adaptation of sensory nerves to mechanical stimulation is whether the electrophysiological properties of the neurone per se can support the adaptive response, or whether the adaptation is secondary to the manner in which the nerve ending interacts with the airway tissue. Harper (1991) observed that the adaptation of somata within the dorsal root ganglia to prolonged suprathreshold depolarizing current steps mimicked the adaptation of the nerve endings arising from these somata to

The Role of Vagal Afferent Nerves in Chronic Obstructive Pulmonary Disease

“…The terminals are exquisitely sensitive to a punctate mechanical "touch" stimulus applied to the mucosa. The nerves respond primarily to the dynamic phase of a rampand-hold mechanical stimulus applied to the mucosa, thus resembling a rapidly adapting response (7). Unlike RAR nerves, however, these fibers are relatively insensitive to smooth muscle constriction or stretch (longitudinal or circumferential).…”

Central nervous system control of the laryngeal muscles in humans

“…On the other hand, the afferents involved in cough are located in the tracheal bifurcation and are also thought to have their cell bodies in the nodose ganglion although in the guinea pig these are contained in the jugular ganglion (McAlexander et al, 1999). The dorsal swallowing center in the nucleus tractus solitarius contains central patterning for swallowing with input to the laryngeal motor neurons via the solitari-ambiguus pathway (Jean, 2001).…”

The effect of spinal cord injury on vagal afferents.

“…Earlier research has shown that the adaptation response which underlies these two vagal populations in the lungs highly correlates with embryological origin (nodose versus jugular) (McAlexander et al, 1999). Afferent fibers from the placode-derived nodose ganglion, predominately rapidly adapt, whereas the majority of fibers that originate from the neural crest-derived jugular ganglion adapt slowly (McAlexander et al, 1999). It is noted that the adaptation response initiated at terminal endings does not always equate with the same electrophysiological response present at the soma (McAlexander et al, 1999).…”

“…For instance, mechanosensitive vagal afferents innervating the lungs have been shown to fall into either slowly adapting receptors (a burst of APs which are maintained as long as the stimulus is present) or rapidly adapting receptors (a brief burst of APs, after which, they rapidly adapt and may cease firing) (Knowlton andLarrabee, 1946, Widdicombe, 1954). Earlier research has shown that the adaptation response which underlies these two vagal populations in the lungs highly correlates with embryological origin (nodose versus jugular) (McAlexander et al, 1999). Afferent fibers from the placode-derived nodose ganglion, predominately rapidly adapt, whereas the majority of fibers that originate from the neural crest-derived jugular ganglion adapt slowly (McAlexander et al, 1999).…”

“…Afferent fibers from the placode-derived nodose ganglion, predominately rapidly adapt, whereas the majority of fibers that originate from the neural crest-derived jugular ganglion adapt slowly (McAlexander et al, 1999). It is noted that the adaptation response initiated at terminal endings does not always equate with the same electrophysiological response present at the soma (McAlexander et al, 1999). This feature may be particularly relevant when considering the use of pharmaceuticals as ionic channel blockers for studies/therapies.…”