Comparison of SLN-evoked swallows during rest and chewing in the freely behaving rabbit

Interactions between the swallowing central neural pathway and the chewing central neural pathway were examined in freely behaving, unanesthetized rabbits. Pharyngeal swallows were elicited by electrical stimulation of the superior laryngeal nerve (SLN) and defined by thyrohyoid muscle (TH) activity in the electromyogram (EMG). Recordings were obtained from rabbits at rest and during chewing. The number of swallows elicited by the SLN stimulation was significantly increased (P<0.001) during quiet oral function (at rest) and during chewing. The increased number of swallows from each baseline was similar, signifying that the effect of the SLN stimulation was similar in generating swallowing in both groups. The swallows induced with SLN stimulation were very similar to natural swallows as defined by the temporal pattern of the EMG duration and the timing of EMG activities. Our results suggest that: (1). the peripheral inputs to the swallowing pathway may rarely be modulated by the chewing pathway in the generation of swallows; (2). the swallowing pathway and the chewing pathway may interact at the level of the rhythm generators; (3). each animal has its own threshold for eliciting pharyngeal swallowing, and the threshold may be independent of the number of chews.