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 chloralose-anesthetized cats. Both vagoaortic nerves were cut, and both sinus nerves were left intact. Each neuron, based on the presence of cardiac and respiratory rhythmicities in its resting activity and reaction to systemic hypoxia (10% O₂ in N₂ for 2 min), was classified into one of three classes. Class I neurons (n = 29, 64%) were activated during systemic hypoxia and had a pronounced cardiac and inspiration-related rhythmicity in their resting activity. Class II neurons (n = 12, 27%) were inhibited during systemic hypoxia, and their cardiac and respiratory rhythmicities were either negligible or totally absent. Class III neurons (n = 4, 9%), similarly to class I, had a pronounced cardiac and inspiratory rhythmicity but were not affected by systemic hypoxia. The systemic hypoxia was always accompanied by an increase in blood pressure. We conclude that class I and possibly class III neurons innervate the arteries of upper airways. We also discuss the possibility that class II neurons are responsible for regulating the smooth muscles of upper airways.