PROPERTIES OF POSTGANGLIONIC SYMPATHETIC FIBERS ISOLATED FROM THE RIGHT RECURRENT LARYNGEAL NERVE

The pattern of response of 45 single postganglionic sympathetic axons dissected from the right recurrent laryngeal nerve was examined in chl oralose-anesthetized cats. Both vagoaortic nerves were cut, and both s inus nerves were left intact. Each neuron, based on the presence of ca rdiac and respiratory rhythmicities in its resting activity and reacti on to systemic hypoxia (10% O-2 in N-2 for 2 min), was classified into one of three classes. Class I neurons (n = 29, 64%) were activated du ring systemic hypoxia and had a pronounced cardiac and inspiration-rel ated rhythmicity in their resting activity. Class II neurons (n = 12, 27%) were inhibited during systemic hypoxia, and their cardiac and res piratory rhythmicities were either negligible or totally absent. Class III neurons (n = 4, 9%), similarly to class I, had a pronounced cardi ac and inspiratory rhythmicity but were not affected by systemic hypox ia. The systemic hypoxia was always accompanied by an increase in bloo d pressure. We conclude that class I and possibly class III neurons in nervate the arteries of upper airways. We also discuss the possibility that class II neurons are responsible for regulating the smooth muscl es of upper airways.