Facilitation of reflex swallowing from the pharynx and larynx.

To evaluate the cooperative effect of afferent signals from the pharynx and larynx on reflex swallowing, the interactive effect of afferent signals from the pharyngeal branch of the glossopharyngeal nerve (GPN-ph) and superior laryngeal nerve (SLN) was analyzed in detail in urethane-anesthetized rats. The electromyographic activity of the mylohyoid muscle was recorded as an indicator of swallowing activity. The onset latency of reflex swallowing was measured to evaluate the effects of electrical stimulation of these nerves, and found to become shorter following an increase in the GPN-ph and/or SLN stimulus frequency. During simultaneous electrical stimulation of the GPN-ph and SLN (frequency: 5-10 Hz, intensity: 30 muA, duration: 1.0 ms for each), the onset latency of reflex swallowing became shorter than that for stimulation of each nerve independently. The present findings suggest that spatiotemporal summation of afferent signals from the GPN-ph and SLN results in an increase of motoneuronal activity in the medullary swallowing center, thus enhancing reflex swallowing.