Inspiratory-activated and inspiratory-inhibited airway vagal preganglionic neurons in the ventrolateral medulla of neonatal rat are different in intrinsic electrophysiological properties

This study investigates the firing properties of the inspiratory-activated and inspiratory-inhibited airway vagal preganglionic neurons located in the external formation of the nucleus ambiguus. The results showed that inspiratory-activated and inspiratory-inhibited neurons are distributed with different density and site preference in this area. Inspiratory-inhibited neurons exhibit significantly more positive resting membrane potential, more negative voltage threshold and lower minimal current required to evoke an action potential under current clamp. The afterhyperpolarization in inspiratory-activated neurons was blocked by apamin, a blocker of the small-conductance Ca(2+)-activated K(+) channels; and that in inspiratory-inhibited neurons by charybdotoxin, a blocker of the large-conductance Ca(2+)-activated K(+) channels. Under voltage clamp, depolarizing voltage steps evoked tetrodotoxin-sensitive rapid inward sodium currents, 4-aminopyridine-sensitive outward potassium transients and lasting outward potassium currents. 4-Aminopyridine partially blocked the lasting outward potassium currents of inspiratory-activated neurons but was ineffective on those of inspiratory-inhibited neurons. These findings suggest that inspiratory-activated and inspiratory-inhibited neurons are differentially organized and express different types of voltage-gated ion channels.