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Galanin (GAL) is a nociceptive transmitter or modulator in the trigeminal sensory system. In this study, GAL expression was investigated in the rat dura mater to demonstrate its possible function in headache using immunohistochemical techniques. The cerebral falx and cerebellar dura mater received abundant blood and nerve supply, and were significantly thicker compared to other portions in the cerebral dura mater. GAL-immunoreactivity was expressed by cell and nerve fiber profiles. Presumed macrophages and dendritic cells contained GAL-immunoreactivity, and co-expressed with CD11b-immunoreactivity. Many isolated and perivascular nerve fibers also showed GAL-immunoreactivity. In addition, GAL-immunoreactive nerve fibers were present in the vicinity of macrophages and dendritic cells with either GAL- or ED1-immunoreactivity. GAL-immunoreactive cells and nerve fibers were common in the cerebral falx and cerebellar dura mater and infrequent in other portions. And, GAL-immunoreactive nerve fibers usually co-expressed calcitonin gene-related peptide (CGRP)-immunoreactivity. In the trigeminal ganglion, a substantial proportion of sensory neurons innervating the dura mater contained GAL-immunoreactivity (mean ± SD, 3.4 ± 2.2%), and co-expressed CGRP-immunoreactivity (2.7 ± 2.1%). The present study may suggest that GAL is associated with nociceptive transduction or modulation in the dura mater. GAL also possibly plays a role in the immune mechanism of the dura mater.

Transient receptor potential melastatin-3 (TRPM3) is a nonselective cation channel, has permeability of Ca2+, 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.

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.

Background Alpha-synuclein (Syn), an unfolded soluble cytosolic protein, is known as a disease-associated protein in the brain. However, little is known about distribution of this protein in the peripheral nervous system. In this study, expression of Syn was investigated in the sensory ganglia of the cranial nerves V, IX and X. Methods To analyze distribution of Syn and its co-expression with calcitonin gene-related peptide (CGRP) or the transient receptor potential cation channel subfamily V member 1 (TRPV1), immunohistochemical techniques were used in the rat cranial sensory ganglia and their peripheral tissues. Results Syn-immunoreactive (-ir) neurons were abundant in the sensory ganglia of the petrosal (56.7%), jugular (28.3%) and nodose ganglia (82.5%). These neurons had small to medium-sized cell bodies (petrosal, mean ± S.D. = 667.4 ± 310.8 μ m2; jugular, 625.1 ± 318.4 μ m2; nodose, 708.3 ± 248.3 μ m2), and were distributed throughout the ganglia. However, the trigeminal ganglion was mostly free of Syn-ir neurons. By double and triple immunofluorescence staining, Syn-ir neurons co-expressed CGRP and TRPV1 in the petrosal and jugular ganglia. Syn-immunoreactivity was expressed by nerve fibers in the epithelium and taste bud of oral and cervical viscerae. These nerve fibers were abundant in the naso-pharynx, epiglottis and laryngeal vestibule. Some taste bud cells were also immunoreactive for Syn. In addition, Syn-ir nerve fibers were detected in the vicinity of macrophages, dendritic cells and Langerhans cells. Conclusions Syn was abundant in the visceral sensory neurons but not in somatic sensory neurons. This protein may play a role in nociceptive and chemosensory transduction in the glossopharyngeal and vagal sensory ganglia. It is possible that Syn has a function about the immune mechanism of the upper air way.