Analysis of transient receptor potential vanilloid 1 and substance P gene expression in the mouse tongue following oral ginger administration

Ginger rhizome (Zingiber officinale) exhibits multiple pharmacological actions. For example, its pungent components target the transient receptor potential vanilloid 1 (TRPV1) ion channel and thus contribute to swallowing reflex recovery by elevating the neuropeptide substance P. However, the precise mechanism underlying this action remains unclear. To examine TRPV1 and substance P gene expression in the mouse tongue in response to stimulation by orally administered ginger, quantitative real-time polymerase chain reaction and immunohistochemistry were performed to evaluate mRNA and protein expression. TRPV1 mRNA expression in the mouse tongue was upregulated 30 min after oral ginger stimulation. In the gingerstimulated mouse, TRPV1 protein expression was increased and concentrated in the plasma membranes of the mucous glandular cells of the tongue epithelium. No significant differences in substance P mRNA expression relative to the control were observed after ginger stimulation. However, immunohistochemistry revealed that the amount of substance P protein expression increased in the mucous glandular cells of the tongue epithelium in ginger-stimulated mice, and this expression appeared to concentrate in the secretory granules of these cells. Activation of TRPV1 promotes the secretion of substance P in saliva, and clinically, saliva levels of substance P can be measured noninvasively and can provide a useful biomarker of the swallowing function. An increased level of substance P in the saliva could indicate improved dysphagia. Our data suggest that ginger activates TRPV1 and promotes the secretion of substance P in saliva. Ginger is therefore expected to serve as a functional agent for improving dysphagia.