Yorinobu, UCHIYAMA, Rika, YAHAGI, Kazuhisa, OKUDA-AKABANE, Norio, MATSUMOTO, 研究, Original, 岩手医科大学歯学部口腔生理学講座, 岩手医科大学歯学部歯科補綴学第一講座, Department of Oral Physiology, School of Dentistry, Iwate Medical University, and Department of Removable Prosthodontics, School of Dentistry, Iwate Medical University
Both voluntary and reflex components are involved in normal swallowing. Swallowing depends on the bulbar central pattern generator (CPG). Therefore, the relationship between the voluntary component (central input) and reflex component (sensory input) may be important to understand the central mechanisms for deglutition. There are water receptors, mechanoreceptors (tactile receptors and deep mechanoreceptors) and taste receptors in the oral mucosa. In this study, the role of sensory receptors in voluntary swallowing was investigated. Twenty healthy volunteers (mean±SD, 28.9±9.7 years) were enrolled in this study. A fine tube was inserted into the pharyngolaryngeal region (PL) or the tongue base (TB). Stimulating solution at room temperature was delivered into the PL or the TB through this tube. Each subject was instructed to repeat swallowing as fast as possible. EMG activity was recorded from suprahyoid muscles during swallowing. The swallowing interval (SI) between two consecutive swallows in each infusion was measured. SIs were shorter in the case of water infusion into the PL than in the case of water infusion into the TB, suggesting that water receptors are localized in the PL. Infusion of 0.15M NaCl into the PL prolonged SI, because 0.15M NaCl inhibits water receptors. However, infusion of 0.15M NaCl into the TB shortened SI, suggesting that excitation of Na^+taste receptors can facilitate voluntarily swallowing. SI with resting saliva infusion into the PL was almost the same as that with water infusion, suggesting that resting saliva can excite water receptors. In the weak mechanical stimulation (infusion rate of 0.2ml/min), SIs varied greatly from subject to subject. Therefore, the variation in SI cannot be explained by difference in sensitivity of the mucosal receptors among subjects. It appears that the ability of CPG to perform repetitive voluntary swallowing varies greatly in subjects. The strong mechanical stimulation (infusion rate of 5.0ml/min) did not influence SI in a subject showing short SI with the weak stimulation, but it shortened SI in a subject showing long SI. This suggests that excitation of oral mucosal receptors strongly compensates for difficulty in swallowing in subjects showing a long SI.