ANATOMICAL AND ELECTROPHYSIOLOGICAL COMPARISON OF THE SENSORY INNERVATION OF BRONCHIAL AND TRACHEAL PARASYMPATHETIC GANGLION NEURONS

Anatomical and electrophysiological techniques were used to examine di fferences in the level of sensory nerve terminals localized in parasym pathetic ganglia in guinea pig trachea and bronchus. We quantified sub stance-P-immunoreactive nerve terminal profiles within the ganglia and the amplitude of capsaicin-sensitive depolarization (slow excitatory postsynaptic potential or sEPSP) evoked by vagus (bronchial) or recurr ent (tracheal) nerve-stimulation. Substance-P-immunoreactive axon prof iles per intrinsic tracheal neuron were fewer in number than per bronc hial ganglion neuron. The average amplitude and duration of the capsai cin-sensitive sEPSPs were similar in tracheal and bronchial ganglion n eurons. Furthermore, capsaicin evoked a nearly equal depolarization of bronchial and tracheal ganglion neurons. The sEPSPs were reduced in b oth areas by a selective neurokinin-3 receptor antagonist, SR142801. T hese results demonstrate that although the number of sensory nerve fib ers in tracheal ganglia an significantly less than those in the bronch us, this did not translate to an obvious physiological difference in s EPSP amplitude.