INTERGANGLIONIC SEGREGATION OF DISTINCT VAGAL AFFERENT FIBER PHENOTYPES IN GUINEA-PIG AIRWAYS

1. The present study addressed the hypothesis that jugular and nodose vagal ganglia contain the somata of functionally and anatomically dist inct airway afferent fibres. 2. Anatomical investigations were perform ed by injecting guinea-pig airways with the neuronal tracer Fast Blue. The animals were killed 7 days later, and the ganglia were removed an d immunostained with antisera against substance P (SP) and neurofilame nt protein (NF). In the nodose ganglion, NF-immunoreactive neurones ac counted for about 98% of the Fast Blue-labelled cells while in the jug ular ganglion they accounted for approximately 49%. SP and NF immunore activity was never (n = 100) observed in the same cell suggesting that the antisera labelled distinct populations. 3. Electrophysiological i nvestigations were performed using an in vitro guinea-pig tracheal and bronchial preparation with intact afferent vagal pathways, including nodose and jugular ganglia. Action potentials arriving from single air way afferent nerve endings were monitored extracellularly using a glas s microelectrode positioned near neuronal cell bodies in either gangli on. 4. The nodose ganglion contained the somata of mainly fast-conduct ing tracheal A delta fibres whereas the jugular ganglion contained equ al numbers of C fibre and A delta fibre tracheal afferent somata. The nodose A delta neurones adapted rapidly to mechanical stimulation, had relatively low mechanical thresholds, were not activated by capsaicin and adapted rapidly to a hyperosmotic stimulus. By contrast, jugular A delta and C fibres adapted slowly to mechanical stimulation, were of ten activated by capsaicin, had higher mechanical thresholds and displ ayed a slow adaptation to a hyperosmotic stimulus. 5. The anatomical, physiological and pharmacological data provide evidence to support the contention that the vagal ganglionic source of the fibre supplying th e airways ultimately dictates its neurochemical and physiological phen otype.