Intracellular analysis of respiratory-modulated hypoglossal motoneurons in the cat.

Intracellular recordings from hypoglossal motoneurons in the brainstem of cats are described, along with postsynaptic potentials evoked by superior laryngeal, vagal and carotid sinus nerve stimulation. The study concentrates on hypoglossal motoneurons with respiratory-related discharge, which can be categorized into inspiratory, inspiratory/early-expiratory and expiratory patterns. Seven cells were labelled with horseradish peroxidase, their location and morphology are described. Stimulation of laryngeal receptors by balloon inflation or by water injection into the larynx, or mimicked by electrical stimulation of the superior laryngeal nerve results in enhanced postinspiratory activity in those cells (inspiratory/early-expiratory, expiratory) already receiving postinspiratory excitation; or actually produces a wave of postinspiratory depolarization in cells (inspiratory) previously quiescent during that period. It is concluded that the firing pattern of the respiratory-modulated hypoglossal motoneurons is unlikely to be static but depends on other factors, one of these being the level of ongoing, or previous laryngeal receptor stimulation.