Central ghrelin inhibits reflex swallowing elicited by activation of the superior laryngeal nerve in the rat

The effect of ghrelin on rhythmic reflex swallowing was examined in urethane–chloralose anesthetized rats. Swallowing was monitored by recording electromyographic activities of the suprahyoid muscle. Fourth ventricular administration of ghrelin decreased swallowing frequency during electrical stimulation of the central cut end of the superior laryngeal nerve (SLN stimulation). A significant decrease in swallowing frequency was observed after ghrelin administration at doses of 3, 10, 30 and 100 pmol. The administration of ghrelin with growth hormone secretagogue receptor antagonist ([D-Lys3] GHRP-6) did not change swallowing frequency during SLN stimulation. Neither mean blood pressure nor heart rate changed after the administration of 10 pmol ghrelin. Bilateral vagotomy did not disrupt the ghrelin response. These observations indicate that the ghrelin response does not depend on either cardiovascular or abdominal responses. Microinjection of ghrelin (0.3 pmol) into the vicinity of the solitary tract inhibited swallowing induced by SLN stimulation. Fourth ventricular administration of orexin-A (3 nmol) also inhibited reflex swallowing elicited by SLN stimulation. These results suggest that ghrelin and other orexigenic peptides inhibit reflex swallowing by modifying neural activities of the dorsal medulla where the swallowing center is housed.