The transient receptor potential cation channel subfamily V members 1 and 2, P2X purinoceptor 3 and calcitonin gene-related peptide in sensory neurons of the rat trigeminal ganglion, innervating the periosteum, masseter muscle and facial skin.

OBJECTIVE: Distribution of the transient receptor potential cation channel subfamily V members 1 (TRPV1) and 2 (TRPV2), and P2X purinoceptor 3 (P2 × 3) was investigated in rat trigeminal ganglion neurons innervating the periosteum, masseter muscle and facial skin.

DESIGN: Double immunofluorescence method for TRPV1 and TRPV2 ion channels or ATP receptor P2 × 3 with calcitonin gene-related peptide (CGRP) was performed on trigeminal ganglion neurons retrogradely labeled from the mandibular periosteum, masseter muscle, or facial skin in 15 male Wistar rats.

RESULTS: The cell size of periosteum neurons (mean ± S.D. = 810.7 ± 36.1 μ m2 ) was smaller than that of masseter muscle neurons (927.0 ± 75.6 μ m2 ), and larger than that of facial skin neurons (661.3 ± 82.2 μ m2 ). Periosteum neurons contained TRPV1- (26.7%), TRPV2- (47.1%) and P2 × 3-immunoreactivity (50.1%). Expression of TRPV2-immunoreactivity was more abundant among periosteum neurons than among facial skin neurons (16.1%). Regarding to TRPV1 and P2 × 3 expression, however, there was no significant difference between periosteum neurons and, masseter muscle and facial skin neurons. TRPV1- immunoreactive trigeminal ganglion neurons which innervated the periosteum, masseter muscle and facial skin mostly had small and medium-sized cell bodies, whereas TRPV2- and P2 × 3-immunoreactive trigeminal ganglion neurons innervating those tissues were of various cell body sizes. Approximately 20% of periosteum (19.2%), masseter muscle (19.2%) and facial skin (21.5%) neurons contained both TRPV1- and CGRP-immunoreactivity. Some periosteum neurons also co-expressed CGRP-immunoreactivity with TRPV2- (10.9%) or P2 × 3- immunoreactivity (11.1%). Distributions of perivascular and free nerve fibers containing CGRP and either TRPV1, TRPV2, or P2 × 3 were occasionally very similar in the mandibular periosteum.

CONCLUSIONS: The present study indicated that trigeminal ganglion nociceptors innervating the periosteum as well as those innervating the masseter muscle and facial skin have vanilloid, acidic, thermal, mechanical and ATP sensors. In some periosteum neurons, CGRP may act as inflammatory mediator through activation of TRPV1, TRPV2 and P2 × 3.