Suppression of jaw-opening and trigemino-hypoglossal reflexes during swallowing in the cat

law-opening and trigemino-hypoglossal reflexes can be evoked by innocuous a s well as noxious afferents from intra-oral structures. It has been reporte d that the amplitude of the jaw-opening reflex evoked by weak electrical st imulation of the upper lip is subject not only to tonic suppression but als o to phase-linked modulation during mastication. In this study, we investig ated whether the jaw-opening and trigemino-hypoglossal reflexes are modulat ed during swallowing. Data were obtained from 8 chloralose-anesthetized cat s. Reflexes were monitored by electromyographic activities recorded from th e anterior digastric, genioglossus, and styloglossus muscles and, after par alysis, by the efferent discharge in the digastric and hypoglossal nerves. Swallowing was elicited either by water dropped on the tongue or by repetit ive stimulation of the superior laryngeal nerve. Jaw-opening and trigemino- hypoglossal reflexes were evoked by stimulation of the lingual nerve, and t he evoked afferent volley was recorded from the Gasserian ganglion so that the threshold of the lingual nerve could be determined, The following resul ts were obtained: (1) The jaw-opening and trigemino-hypoglossal reflexes ev oked by stimulation of the low-threshold, but not high-threshold, lingual a fferents were remarkably suppressed during swallowing; and (2) both the jaw -opening and trigemino-hypoglossal reflexes evoked by low-threshold lingual afferents were suppressed during fictive swallowing after the animals were paralyzed. We conclude that the jaw-opening and trigemino-hypoglossal refl exes evoked by low-threshold lingual afferents are suppressed during swallo wing by a central motor program.