Sour taste stimulation facilitates reflex swallowing from the pharynx and larynx in the rat

Chemical stimulation of the pharynx and larynx is effective in eliciting reflex swallowing. A sour taste bolus facilitates the onset of swallowing in patients with neurogenic dysphagia, but the mechanism of the facilitation has not been clarified. We investigated the effect of sour solutions on the elicitation of reflex swallowing in anesthetized rats. The main ducts of salivary glands were ligated to avoid the effect of saliva. A small amount of water, sour solutions, and other taste solutions were applied to the mucosa of the pharyngolaryngeal region. Acetic acid and citric acid, which provide a sour taste, had a stronger effect on evoking reflex swallowing as compared with other taste solutions. The effectiveness of these acids increased with increasing concentrations. We also examined the contribution of the superior laryngeal nerve (SLN) and the pharyngeal branch of the glossopharyngeal nerve (GPNph) to reflex swallowing. Acetic acid was greatly effective in evoking swallowing in both the region innervated by the SLN and the GPNph. On the other hand, water was effective in the SLN region but only slightly effective in the GPNph region. The results indicate that stimulation of the pharyngolaryngeal region with sour solutions facilitates reflex swallowing, suggesting that the facilitation may be due to increases of sensory inputs via the SLN and GPNph.