Effect of stimulation of the laryngopharynx with water and salt solutions on voluntary swallowing in humans: characteristics of water receptors in the laryngopharyngeal mucosa.

Stimulation of water receptors in the laryngopharynx (LP) with water facilitates voluntary swallowing in humans. Based on measures of swallowing intervals (SIs) in repetitive swallowing, we investigated characteristics of laryngopharyngeal water receptors in humans. Healthy adult volunteers were instructed to perform repetitive swallowing as quickly as possible during infusion of a solution into the LP. Infusion of water shortened SI, suggesting that water excites water receptors. Infusion of 0.3 M NaCl solution prolonged SI, suggesting that the NaCl solution inhibits activity of water receptors. SI increased with increasing concentration of NaCl. Anion or cation substitutions indicated that excitation of water receptors is due to absence or reduced concentration of Cl(-). With diminution of peripheral inputs, cortical inputs would play a dominant role in voluntary swallowing. With infusion of a nonstimulating solution (0.3 M NaCl at 0.2 mL/min), SI varied greatly from subject to subject, suggesting that the ability of central regulation of swallowing to initiate repetitive voluntary swallowing varies among subjects. Facilitation of swallowing by chemosensory inputs from water receptors appeared strongly in subjects with longer SI with infusion of the nonstimulating solution. It appears that chemosensory activation compensates for the difficulty in initiating swallowing via the central neural mechanism.