SUPERIOR LARYNGEAL NERVE-STIMULATION IN THE CAT - EFFECT ON OROPHARYNGEAL SWALLOWING, ESOPHAGEAL MOTILITY AND LOWER ESOPHAGEAL SPHINCTER ACTIVITY

Superior laryngeal nerve (SLN) stimulation can activate the brainstem swallowing mechanism to produce a complete swallowing sequence consist ing of oropharyngeal, oesophageal and lower oesophageal sphincter (LOS ) components. However, little is known of the effect of SLN stimulatio n (peripheral-sensory input from the pharynx) on the characteristics o f oesophageal motor activity, especially in the smooth muscle portion. The present study examined the effect of varying stimulus train lengt h and frequency on each of the three components of the reflex. Acute s tudies were performed in urethane anaesthetized cats. Oesophageal moti lity was monitored using conventional manometric techniques, and oroph aryngeal swallowing by the mylohyoid electromyogram. SLN stimulus trai n length (1-10 sec) and frequency (5-30 Hz) were varied independently. Increased train length or frequency resulted in (1) an increase in or opharyngeal swallowing and incidence of the complete swallowing respon se, (2) an increase in latency to onset of the oesophageal peristaltic wave, (3) reduction of the amplitude of the evoked peristaltic contra ction in the smooth muscle portion, without altering its velocity, (4) increased LOS relaxation, and increased LOS after contraction. The LO S contraction was abolished by atropine (100 mu g kg(-1)). Therefore, increased SLN stimulation not only results in excitation of the centra l swallowing program and the oropharyngeal stage of swallowing but has major effects on the oesophageal and LOS stages of swallowing. Affere nt SLN stimuli can impact on the control mechanisms for each stage, to inhibit or excite the stages in different ways.