Gustatory stimulation of the oropharynx fails to induce swallowing in the sleeping dog.

Abstract

Very little is known about the influence of sleep in initiation of swallowing in response to gustatory stimulation of the oropharynx. The aim of the present study was to examine the effect of sleep on swallowing. Studies were performed in a group of four dogs trained to sleep naturally in our laboratory. During nasal breathing, tap water, 0.9% NaCl, 0.5 mol/L glucose, 0.5 mol/L NaHCO3, or acetic acid (pH 5.2) were infused at 0.5 mL/s on the dorsum of the tongue using a special feeding tube. The entire surface of the tongue was mapped for initiation of swallowing in the awake and sleeping animal. Swallowing never occurred during non-rapid eye movement and rapid eye movement sleep. Infusion of a solution either did not cause any reaction, resulting in dribbling of the test fluid through the opening between the jaws, or caused arousal that was occasionally followed by a swallow. Arousal-swallow complex occurred most significantly after application of acid and when the fluid was applied to the posterior tongue area. Wakefulness is a prerequisite for swallowing.