Abstract
In humans, Shingai et al. (1989) demonstrated that distilled water (DW) and NaCl solutions applied to the posterior tongue are effective for elicitation of swallowing reflex. They showed that excitation of water-sensitive receptors (WS-Rs) and salt taste receptors (S-Rs) elicits the swallowing reflex, but the precise sites of these receptors remain unclear. In the present study, the properties of the WS-Rs and S-Rs responsible for the swallowing reflex in humans were investigated. Each subject was instructed to repeat swallowing as fast as possible. DW or 0.05-0.3 M NaCl solution was delivered to the posterior tongue through a fine tube at a slow rate of 0.2 ml/min. The tip of the tube was located in the pharyngolaryngeal region (PL-R), where 0.3 M NaCl did not give rise to salty taste. The intervals between two consecutive swallowings in a test were measured. Swallowing interval was shortest when DW was used, and the interval increased with increase in NaCl concentration. The mean interval when 0.3 M NaCl was used was the same as that in the case of olive oil, which does not activate chemoreceptors, suggesting that 0.3 M NaCl inhibits excitation of WS-Rs. The present results suggest that WS-Rs for swallowing reflex reside in the PL-R, whereas S-Rs do not reside in this region. The tip of the infusion tube was moved to the dorsal tongue, where NaCl give rise to salty taste. Infusion of 0.15 M NaCl led to much shorter intervals than did DW. This suggests that S-Rs for swallowing reflex reside in the tongue, whereas WS-Rs do not reside in this region. [Jpn J Physiol 55 Suppl:S159 (2005)]
