title: Involvement of Microglial P2Y12 Signaling in Tongue Cancer Pain.
abstract: To elucidate if microglial P2Y12 receptor (P2Y12R) mechanisms are involved in the trigeminal spinal subnucleus caudalis (Vc; also known as the medullary dorsal horn) in intraoral cancer pain, we developed a rat model of tongue cancer pain. Squamous cell carcinoma (SCC) cells were inoculated into the tongue of rats; sham control rats received the vehicle instead. Nociceptive behavior was measured as the head-withdrawal reflex threshold (HWRT) to mechanical or heat stimulation applied to the tongue under light anesthesia. On day 14 after the SCC inoculation, activated microglia and P2Y12R expression were examined immunohistochemically in the Vc. The HWRT was also studied in SCC-inoculated rats with successive intra-cisterna magna (i.c.m.) administration of specific P2Y12R antagonist (MRS2395) or intraperitoneal administration of minocycline, a microglial activation inhibitor. Tongue cancer was histologically verified in SCC-inoculated rats, within which the HWRT to mechanical stimulation of the tongue was significantly decreased, as compared with that of vehicle-inoculated rats, although the HWRT to heat stimulation was not. Microglia was strongly activated on day 14, and the administration of MRS2395 or minocycline reversed associated nocifensive behavior and microglial activation in SCC-inoculated rats for 14 d. The activity of Vc wide dynamic range nociceptive neurons was also recorded electrophysiologically in SCC-inoculated and sham rats. Background activity and noxious mechanically evoked responses of wide dynamic range neurons were significantly increased in SCC-inoculated rats versus sham rats, and background activity and mechanically evoked responses were significantly suppressed following i.c.m. administration of MRS2395 in SCC-inoculated rats as compared with sham. The present findings suggest that SCC inoculation that produces tongue cancer results in strong activation of microglia via P2Y12 signaling in the Vc, in association with increased excitability of Vc nociceptive neurons, reflecting central sensitization and resulting in tongue mechanical allodynia.
authors.affiliation: Department of Oral and Maxillofacial Surgery, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Tamagawa
authors.affiliation: Department of Physiology, Nihon University School of Dentistry, Tokyo, Japan Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, Tokyo, Japan shinoda.masamichi@nihon-u.ac.jp.
authors.forename: M
authors.initials: M
authors.lastname: Shinoda
authors.affiliation: Department of Physiology, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Honda
authors.affiliation: Department of Oral and Maxillofacial Surgery, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Furukawa
authors.affiliation: Department of Physiology, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kaji
authors.affiliation: Department of Clinical Medicine, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Nagashima
authors.affiliation: Department of Oral and Maxillofacial Surgery, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: R
authors.initials: R
authors.lastname: Akasaka
authors.affiliation: Department of Physiology, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Chen
authors.affiliation: Department of Oral Physiology, Faculty of Dentistry, University of Toronto, Toronto, Canada.
authors.forename: B J
authors.initials: BJ
authors.lastname: Sessle
authors.affiliation: Department of Oral and Maxillofacial Surgery, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yonehara
authors.affiliation: Department of Physiology, Nihon University School of Dentistry, Tokyo, Japan Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Iwata
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000072716:Cancer Pain / Q000378:metabolism*; D002294:Carcinoma, Squamous Cell / Q000378:metabolism*; D007150:Immunohistochemistry; D008297:Male; D017628:Microglia / Q000378:metabolism*; D008911:Minocycline / Q000494:pharmacology; D009437:Neuralgia / Q000378:metabolism*; D009619:Nociceptors / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D058925:Receptors, Purinergic P2Y12 / Q000378:metabolism*; D015398:Signal Transduction; D014062:Tongue Neoplasms / Q000378:metabolism*; D014279:Trigeminal Nucleus, Spinal / Q000378:metabolism*; D014631:Valerates / Q000494:pharmacology
chemical_list: C528918:2,2-dimethylpropionic acid 3-(2-chloro-6-methylaminopurin-9-yl)-2-(2,2-dimethylpropionyloxymethyl)propyl ester; D058925:Receptors, Purinergic P2Y12; D014631:Valerates; D008911:Minocycline; D000225:Adenine
keywords: chronic pain; medulla; microglia; purinergic receptor; squamous cell carcinoma; trigeminal nerve