The Distribution of TRPV1 and TRPV2 in the rat pharynx

Immunohistochemistry for two nociceptive transducers, the transient receptor potential cation channel subfamily V members 1 (TRPV1) and 2 (TRPV2), was performed on the pharynx and its adjacent regions. TRPV1-immunoreactivity (IR) was detected in nerve fibers beneath and within the epithelium and/or taste bud-like structure. In the pharynx, these nerve fibers were abundant in the naso-oral part and at the border region of naso-oral and laryngeal parts. They were also numerous on the laryngeal side of the epiglottis and in the soft palate. TRPV2-IR was expressed by dendritic cells in the pharynx and epiglottis, as well as in the root of the tongue and soft palate. These cells were located in the epithelium and lamina propria. TRPV2-immunoreactive (IR) dendritic cells were numerous in the naso-oral part of the pharynx, epiglottis, and tongue. Abundance of TRPV2-IR dendritic processes usually obscured the presence of TRPV2-IR nerve fibers in these portions. However, some TRPV2-IR nerve fibers could be observed in the epithelium of the soft palate. Retrograde tracing method also revealed that sensory neurons which innervate the pharynx or soft palate were abundant in the jugular-petrosal ganglion complex and relatively rare in the nodose ganglion. In the jugular-petrosal ganglion complex, TRPV1- and TRPV2-IR were expressed by one-third of pharyngeal and soft palate neurons. TRPV2-IR was also detected in 11.5 % pharyngeal and 30.9 % soft palate neurons in the complex. Coexpression of TRPV1 and CGRP was frequent among pharyngeal and soft palate neurons. The present study suggests that TRPV1- and TRPV2-IR jugular-petrosal neurons may be associated with the regulation of the swallowing reflex.