title: Contribution of sensitized P2X receptors in inflamed tissue to the mechanical hypersensitivity revealed by phosphorylated ERK in DRG neurons.
abstract: The mechanism of mechanical hyperalgesia in inflammation might involve a 'mechanochemical' process whereby stretch evokes the release of adenosine 5'-triphosphate (ATP) from the damaged tissue that then excites nearby primary sensory nerve terminals. In the present study, phosphorylated extracellular signal-regulated protein kinase (pERK) immunoreactivity was used as a marker indicating functional activation of primary afferent neurons to examine the P2X receptor-mediated noxious response in DRG neurons in a rat model of peripheral inflammation. We found that very few pERK-labeled DRG neurons were detected in normal rats after alpha, beta methylene-ATP (alphabetame-ATP) intraplantar injection. However, a number of DRG neurons were labeled for pERK after alphabetame-ATP injection to the complete Freund's adjuvant (CFA) induced inflamed paw. Seventy-three percent of pERK-labeled DRG neurons co-expressed the P2X3 receptor. After mechanical noxious stimulation to the hind paw of CFA-inflamed rats, we found many more pERK-labeled neurons compared to those in the normal rats. Administration of the P2X3 receptor antagonists, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid or 2'- (or 3')-O-(trinitrophenyl)adenosine 5'-triphosphate (TNP-ATP), significantly decreased the mechanical stimulation-evoked pERK labeling in CFA-inflamed rats, but not in normal rats. We also found the recruitment of neurons with myelinated A fibers labeled for pERK in CFA-inflamed rats, which was reversed by P2X3 receptor antagonists. Moreover, TNP-ATP dose dependently reduced the mechanical hypersensitivity of CFA rats. These data suggest that the P2X receptors in primary afferent neurons increase their activity with enhanced sensitivity of the intracellular ERK signaling pathway during inflammation and then contribute to the hypersensitivity to mechanical noxious stimulation in the inflammatory state.
authors.affiliation: Department of Anatomy and Neuroscience, Hyogo College of Medicine, 1-1 Mukogawa-cho, Nishinomiya, Hyogo 663-8501, Japan.
authors.forename: Yi
authors.initials: Y
authors.lastname: Dai
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fukuoka
authors.forename: Hu
authors.initials: H
authors.lastname: Wang
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yamanaka
authors.forename: Koichi
authors.initials: K
authors.lastname: Obata
authors.forename: Atsushi
authors.initials: A
authors.lastname: Tokunaga
authors.forename: Koichi
authors.initials: K
authors.lastname: Noguchi
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002452:Cell Count; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005620:Freund's Adjuvant; D007839:Functional Laterality / Q000187:drug effects; D005727:Ganglia, Spinal / Q000166:cytology*; D007150:Immunohistochemistry / Q000379:methods; D007249:Inflammation / Q000139:chemically induced / Q000378:metabolism*; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D016900:Neurofilament Proteins / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D010766:Phosphorylation; D010812:Physical Stimulation; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058469:Receptors, Purinergic P2X
chemical_list: D016900:Neurofilament Proteins; D010975:Platelet Aggregation Inhibitors; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; C051774:neurofilament protein H; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D011732:Pyridoxal Phosphate; C045674:2',3'-O-(2,4,6-trinitro-cyclohexadienylidine)adenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D005620:Freund's Adjuvant; D020928:Mitogen-Activated Protein Kinases