Transient receptor potential melastatin-3 in the rat sensory ganglia of the trigeminal, glossopharyngeal and vagus nerves

Transient receptor potential melastatin-3 (TRPM3) is a nonselective cation channel, has permeability of Ca ²⁺ , and probably participates in thermosensitive nociception. In this study, immunohistochemistry for TRPM3 was conducted in the rat trigeminal, glossopharyngeal and vagal sensory ganglia. TRPM3-immunoreactivity was expressed by half of sensory neurons in the trigeminal (TG), petrosal (PG) and jugular ganglia (JG), and by about 80% of sensory neurons in the nodose ganglion (NG). They mostly had small to medium-sized cell bodies. A trichrome immunofluorescence method showed co-existence of TRPM3 with TRP vanilloid 1 (TRPV1) and calcitonin gene-related peptide (CGRP). Approximately 70% of TRPM3-immunoreactive (-IR) neurons contained TRPV1-immunoreactivity in all the examined ganglia. More than 40% of TRPM3-IR neurons exhibited CGRP-immunoreactivity in the TG, PG and JG. Only a few sensory neurons co-expressed TRPM3- and CGRP-immunoreactivity in the NG. In addition, more than 40% of TRPM3-IR neurons bound to isolectin B4 in all the examined ganglia. By combination of retrograde tracing method and immunohistochemistry, half of TG neurons innervating the facial skin and incisive papilla expressed TRPM3-immunoreactivity whereas approximately 20% of those innervating the tooth pulp contained TRPM3-immunoreactivity. Co-expression of TRPM3-immunoreactivity with TRPV1- or CGRP-immunoreactivity was common among cutaneous and papillary TG neurons but not among pulpal TG neurons. More than 60% of PG and JG neurons innervating the external ear canal skin and circumvallate papilla contained TRPM3-immunoreactivity. Co-expression of TRPM3 with TRPV1 or CGRP was common among PG and JG neurons innervating the external ear canal skin. However, a smaller number of TRPM3-IR neurons co-expressing TRPV1- or CGRP-immunoreactivity innervate the circumvallate papilla in the PG. The present study suggests that expression of TRPM3 and its co-existence with TRPV1 and CGRP in sensory neurons depend on the variety of their peripheral targets in the trigeminal, glossopharyngeal and vagal nervous systems.