title: The role of P2X3 receptors in bilateral masseter muscle allodynia in rats.
abstract: OBJECTIVE
  To determine the relationship between bilateral allodynia induced by masseter inflammation and P2X3 receptor expression changes in trigeminal ganglia (TRG) and the influence of intramasseteric P2X3 antagonist administration on bilateral masseter allodynia.
  
  
  METHODS
  To induce bilateral allodynia, rats received a unilateral injection of complete Freund's adjuvant (CFA) into the masseter muscle. Bilateral head withdrawal threshold (HWT) was measured 4 days later. Behavioral measurements were followed by bilateral masseter muscle and TRG dissection. Masseter tissue was evaluated histopathologically and TRG tissue was analyzed for P2X3 receptor mRNA expression by using quantitative real-time polymerase chain reaction (PCR) analysis. To assess the P2X3 receptor involvement in nocifensive behavior, two doses (6 and 60 μg/50 μL) of selective P2X3 antagonist A-317491 were administrated into the inflamed masseter muscle 4 days after the CFA injection. Bilateral HWT was measured at 15-, 30-, 60-, and 120-minute time points.
  
  
  RESULTS
  HWT was bilaterally reduced after the CFA injection (P<0.001). Intramasseteric inflammation was confirmed ipsilaterally to the CFA injection. Quantitative real-time PCR analysis demonstrated enhanced P2X3 expression in TRG ipsilaterally to CFA administration (P<0.01). In comparison with controls, the dose of 6 μg of A-317491 significantly increased bilateral HWT at 15-, 30-, and 60-minute time points after the A-317491 administration (P<0.001), whereas the dose of 60 μg of A-317491 was efficient at all time points ipsilaterally (P=0.004) and at 15-, 30-, and 60-minute time points contralaterally (P<0.001).
  
  
  CONCLUSIONS
  Unilateral masseter inflammation can induce bilateral allodynia in rats. The study provided evidence that P2X3 receptors can functionally influence masseter muscle allodynia and suggested that P2X3 receptors expressed in TRG neurons are involved in masseter inflammatory pain conditions.
authors.affiliation: Petra Tariba Knežević, Department of Prosthodontics, University of Rijeka School of Dental Medicine and School of Medicine, Kreąimirova 40, 51000 Rijeka, Croatia, petra.tariba@uniri.hr.
authors.forename: Petra
authors.initials: P
authors.lastname: Tariba Knežević
authors.forename: Robert
authors.initials: R
authors.lastname: Vukman
authors.forename: Robert
authors.initials: R
authors.lastname: Antonić
authors.forename: Zoran
authors.initials: Z
authors.lastname: Kovač
authors.forename: Ivone
authors.initials: I
authors.lastname: Uhač
authors.forename: Sunčana
authors.initials: S
authors.lastname: Simonić-Kocijan
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D005620:Freund's Adjuvant; D006930:Hyperalgesia / Q000378:metabolism*; D007249:Inflammation / Q000378:metabolism; D008297:Male; D008406:Masseter Muscle / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D010146:Pain / Q000503:physiopathology; D010636:Phenols / Q000494:pharmacology*; D011083:Polycyclic Compounds / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D058477:Receptors, Purinergic P2X3 / Q000096:biosynthesis*; D012668:Trigeminal Ganglion / Q000503:physiopathology*
chemical_list: C470346:A-317491; D010636:Phenols; D011083:Polycyclic Compounds; D058477:Receptors, Purinergic P2X3; D005620:Freund's Adjuvant