Firing properties of identified superior laryngeal neurons in the nucleus ambiguus in the rat.

Superior laryngeal motoneurons control muscles in the larynx and recent work has shown they also have axon collaterals that project to cardiac vagal neurons in the nucleus ambiguus. The present study was undertaken to identify and examine the firing properties of superior laryngeal neurons (SLNs) in the rat. SLNs typically fired spontaneously and repetitively at a rate of 4-7 Hz. The firing was continuous and showed little bursting activity. Firing evoked afterhyperpolarizations were insensitive to apamin but blocked by charybdotoxin. The voltage-gated currents in SLNs consist of a TTX-sensitive Na current and a 4-aminopyridine sensitive K current. It is likely that the activity of these neurons not only control respiratory laryngeal muscles, but may also provide an interaction between the respiratory system and the control of the heart rate.