Capsaicin receptor expression in rat laryngeal innervation

Capsaicin elicits a sensation of burning pain by selectively activating sensory neurons that convey information about noxious stimuli to the central nervous system. Vanilloid receptor subtype 1 (VRI) and the vanilloid receptor-like protein 1 (VRL-1) are activated, not only by capsaicin, but also by noxious heat and protons, and it has been suggested that they are polymodal nociceptors. We investigated the expression of VR1 and VRL-1 in the rat larynx and nodose ganglion using VR1 and VRL-1 immunohistochemical analysis with visualization by diaminobenzidine reaction. Fibers positive for VRL-1 were detected in the laryngeal epithelium and lamina propria. Cells positive for VRL-1 were distributed in the intralaryngeal ganglia. Half of the neurons in the nodose ganglion had VR-1 immunoreactivity, and almost 10% of the nodose ganglion neurons were positive for VRL-1. These findings suggest that these capsaicin receptors play an important role in the nociception of the laryngeal innervation.