Effect of Stimulation of the Laryngopharynx with Water and Salt Solutions on Voluntary Swallowing in Humans: Characteristics of Water Receptors in the Laryngopharyngeal Mucosa

Chemical Senses, Oct 2010

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.

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Effect of Stimulation of the Laryngopharynx with Water and Salt Solutions on Voluntary Swallowing in Humans: Characteristics of Water Receptors in the Laryngopharyngeal Mucosa

Advance Access publication August Effect of Stimulation of the Laryngopharynx with Water and Salt Solutions on Voluntary Swallowing in Humans: Characteristics of Water Receptors in the Laryngopharyngeal Mucosa Yasuyuki Kitada 2 3 Rika Yahagi 1 2 Kazuhisa Okuda-Akabane 0 2 0 Department of Oral Biology, School of Dentistry, Iwate Medical University , 1-3-27 Chuoh-dori, Morioka 020-8505 , Japan 1 Division of Dysphagia Rehabilitation, Department of Oral Biological Science, Niigata University Graduate School of Medical and Dental Sciences , 2-5274 Gakkocho-dori, Chuo-ku, Niigata 951-8514 , Japan 2 a The Author 2010. Published by Oxford University Press. All rights reserved. For permissions , please 3 Morioka Taste and Swallowing Research Institute , 1-15-12 Higashi-Kuroishino, Morioka 020-0108 , Japan 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. human; laryngopharynx; swallowing; taste stimulus; water receptors Introduction Swallowing consists of a reflex sequence of muscle contractions that propels ingested materials and pooled saliva from the mouth to the stomach. Swallowing simultaneously serves to protect the respiratory tract from aspiration. Swallowing can be initiated either voluntarily or reflexively (Miller 1982) . Both inputs from the cerebral cortex and sensory inputs from mucosal receptors in the oropharynx can regulate the activity of the swallowing central pattern generator (CPG) located in the medulla oblongata and the CPG can trigger swallowing (Jean 2001; Ertekin and Aydogdu 2003) . Therefore, there might be interactions between sensory and cortical inputs for initiation of swallowing. However, the interaction between the 2 mechanisms has not been fully elucidated. by NaCl is due to Cl– in rabbits (Shingai 1977) and puppies (Boggs and Bartlett 1982) , whereas Cl– is not a crucial factor for inhibition of water response of water receptors in cats (Stedman et al. 1980) and rats (Shingai 1980) . Therefore, excitation of water receptors involves a diversity of mechanisms. Although taste receptor proteins triggering signal transduction events were identified by means of electrophysiology, molecular biology, genetic approaches, and also screening the mass of genome sequence data (Chandrashekar et al. 2006; Sugita 2006) , molecular mechanism of excitation of water receptors remains elusive. Although water applied to the throat has been used to induce swallowing reflex in humans (Hughes and Wiles 1996; Ertekin et al. 2001) , there are only a few reports on characteristics of water receptors. In humans, Shingai et al. (1989) measured the latency of reflex swallowing induced by application of water or salt solutions to the throat. They showed that water was the most effective stimulus for elicitation of swallowing reflex. Stimulation with solutions of various concentrations of NaCl affected the latency, but their effects were complicated because salt solutions above 0.05 M stimulated salt taste receptors in the posterior tongue (PT). Recently, we were able to stimulate water receptors in the LP in humans without stimulation of salt taste receptors in the PT even though a hypertonic saline solution was used as a stimulant (Yahagi et al. 2008) . That is, solutions were infused into the LP through a fine tube inserted into the LP orally during voluntary swallowing. Repetitive voluntary swallowing makes it possible to withdraw the infused solution from the LP quickly and thereby the solution could stimulate only a limited area of the LP in which water receptors are located. Infusion of water or salt solutions into the LP affected swal (...truncated)


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Kitada, Yasuyuki, Yahagi, Rika, Okuda-Akabane, Kazuhisa. Effect of Stimulation of the Laryngopharynx with Water and Salt Solutions on Voluntary Swallowing in Humans: Characteristics of Water Receptors in the Laryngopharyngeal Mucosa, Chemical Senses, 2010, pp. 743-749, Volume 35, Issue 8, DOI: 10.1093/chemse/bjq079