Intracellular activity of superior laryngeal nerve motoneurons during fictive swallowing in decerebrate rats.

We examined the swallowing-related intracellular activity of motoneurons of the superior laryngeal nerve (SLN) in decerebrate, paralyzed and artificially-ventilated rats, to elucidate the neuronal mechanism of the pharyngo-esophageal and laryngo-esophageal coordination during swallowing. The majority of the SLN motoneurons exhibited respiratory rhythm (n=16; 13 inspiratory, one expiratory and two non-respiratory neurons). During fictive swallowing evoked by electrical stimulation of the SLN, all these motoneurons showed a hyperpolarization-depolarization sequence in their membrane potentials. The hyperpolarization, which was shown to consist of inhibitory postsynaptic potentials, started at the onset of the hypoglossal swallowing burst, lasted during the burst, and was followed by a depolarization at the end of the burst. This hyperpolarization-depolarization pattern implies that the SLN motoneurons may be involved in the 'inhibitory chain' within the swallowing pattern generator, which may be cardinal in the sequential activation of different populations of motoneurons innervating the swallowing-related muscles.