Electrophysiological properties of respiratory laryngeal motoneurons and effects of thiopental.

Transmembrane potentials of the respiratory laryngeal motoneurons were recorded in decerebrate, vagotomized and paralyzed cats. Twenty inspiratory and thirteen postinspiratory neurons were identified. Periodic membrane potential (MP) fluctuations as well as patterns of postsynaptic potentials (PSPs) were characterized in each type of neurons by measuring the input resistance and injecting Cl- to reverse inhibitory PSPs. On the basis of PSP patterns, two subtypes of inspiratory neurons could be distinguished. Thiopental (2-3 mg/kg, i.v.) produced depolarization together with reduction of firing in most laryngeal neurons. Excitatory and inhibitory PSPs were both depressed and MP fluctuations became smaller in each phase of the respiratory cycle. Elevation of the firing threshold and separation of IS-SD spikes often occurred after thiopental. These results suggest that thiopental depresses the laryngeal motoneuron through inhibition of synaptic transmission and of spike generation.