Effects of lingual nerve afferents on swallowing in sheep

We investigated in sheep the effects of stimulation of the thick afferent f ibers running through the lingual nerve (LN) upon the activity of some of t he muscles and medullary interneurons or motoneurons which are active durin g swallowing. Using electromyography (EMG), and extra- and intracellular ne uronal recording, we demonstrated that LN stimulation inhibited triggering and/or distal progression of deglutition reflexly induced by stimulation of the superior laryngeal nerve (SLN). This inhibition appeared as a delay, o r the interruption or total suppression, of the EMG and neuronal swallowing activities, depending on the interval between SLN and LN stimulation. It w as apparent at the lever of the muscles and motoneurons of the nucleus ambi guus, as well as at the level of the interneurons of the dorsal medulla wit hin or around the nucleus of solitary tract, which are assumed to be the co re of the organizing system for swallowing. the so-called central pattern g enerator (CPG). Taking into account the stimulation parameters used in our experiments, it was likely that only LN-mechanosensitive fibers were excite d. These fibers were involved in the jaw-opening reflex, and possibly in ma stication regulation. Therefore, inhibition of swallowing could result from interactions between the hindbrain mastication and swallowing CPGs. Howeve r, it was also possible that mechanosensitive afferents acted upon the swal lowing CPG directly or indirectly through supra-medullary, especially corti cal, loops.