title: The role of ERK signaling and the P2X receptor on mechanical pain evoked by movement of inflamed knee joint.
abstract: Pain during inflammatory joint diseases is enhanced by the generation of hypersensitivity in nociceptive neurons in the peripheral nervous system. To explore the signaling mechanisms of mechanical hypersensitivity during joint inflammation, experimental arthritis was induced by injection of complete Freund's adjuvant (CFA) into the synovial cavity of rat knee joints. As a pain index, the struggle threshold of the knee extension angle was measured. In rats with arthritis, the phosphorylation of extracellular signal-regulated kinase (ERK), induced by passive joint movement, increased significantly in dorsal root ganglion (DRG) neurons innervating the knee joint compared to the naïve rats that received the same movement. The intrathecal injection of a MEK inhibitor, U0126, reduced the phosphorylation of ERK in DRG neurons and alleviated the struggle behavior elicited by the passive movement of the joint. In addition, the injection of U0126 into the joint also reduced the struggle behavior. These findings indicate that the ERK signaling is activated in both cell bodies in DRG neurons and peripheral nerve fibers and may be involved in the mechanical sensitivity of the inflamed joint. Furthermore, the phosphorylated ERK-positive neurons co-expressed the P2X3 receptor, and the injection of TNP-ATP, which antagonizes P2X receptors, into the inflamed joint reduced the phosphorylated ERK and the struggle behavior. Thus, it is suggested that the activation of the P2X3 receptor is involved in the phosphorylation of ERK in DRG neurons and the mechanical hypersensitivity of the inflamed knee joint.
authors.affiliation: Department of Anatomy and Neuroscience, Hyogo College of Medicine, 1-1, Mukogawa-cho, Nishinomiya 663-8501, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Seino
authors.forename: Atsushi
authors.initials: A
authors.lastname: Tokunaga
authors.forename: Toshiya
authors.initials: T
authors.lastname: Tachibana
authors.forename: Shinichi
authors.initials: S
authors.lastname: Yoshiya
authors.forename: Yi
authors.initials: Y
authors.lastname: Dai
authors.forename: Koichi
authors.initials: K
authors.lastname: Obata
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yamanaka
authors.forename: Kimiko
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Koichi
authors.initials: K
authors.lastname: Noguchi
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000627:therapeutic use; D000818:Animals; D001169:Arthritis, Experimental / Q000503:physiopathology*; D001370:Axonal Transport; D002070:Butadienes / Q000627:therapeutic use; D004195:Disease Models, Animal; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology*; D005620:Freund's Adjuvant / Q000633:toxicity; D005727:Ganglia, Spinal / Q000473:pathology; D006930:Hyperalgesia / Q000209:etiology / Q000503:physiopathology; D007270:Injections, Intra-Articular; D007278:Injections, Spinal; D008297:Male; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology; D009570:Nitriles / Q000627:therapeutic use; D020370:Osteoarthritis, Knee / Q000503:physiopathology*; D010146:Pain / Q000209:etiology / Q000503:physiopathology*; D010766:Phosphorylation / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D058919:Purinergic P2 Receptor Antagonists; D016059:Range of Motion, Articular; D051381:Rats; D017207:Rats, Sprague-Dawley; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D058477:Receptors, Purinergic P2X3; D015398:Signal Transduction; D013264:Stifle / Q000294:innervation; D013314:Stress, Mechanical
chemical_list: D002070:Butadienes; D009570:Nitriles; C546410:P2rx3 protein, rat; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058477:Receptors, Purinergic P2X3; C113580:U 0126; C045674:2',3'-O-(2,4,6-trinitro-cyclohexadienylidine)adenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D005620:Freund's Adjuvant; D048049:Extracellular Signal-Regulated MAP Kinases