2--3--o-(2-4-6-trinitrophenyl)adenosine-5--triphosphate and Inflammation

Topics: Adenosine Triphosphate; Animals; Encephalomyelitis, Autoimmune, Experimental; Female; Gene Expression; Inflammation; Ivermectin; Macrophages; Mice; Microglia; Myelin Sheath; Oligodendroglia; Phagocytosis; Purinergic P2X Receptor Antagonists; Rats; Receptors, Purinergic P2X4; Remyelination

The aim of this study was to investigate the role of P2X3, P2X2/3 and P2X7 receptors in the development of TMJ hyperalgesia induced by carrageenan. We also investigated the expression of mRNA of P2X7 receptors in the trigeminal ganglia and the existence of functional P2X7 receptors in the rat's TMJ. The P2X1, P2X3 and P2X2/3 receptor antagonist TNP-ATP, but not the selective P2X7 receptor antagonist A-438079, significantly reduced carrageenan-induced TMJ inflammatory hyperalgesia. The qPCR assay showed that mRNA of P2X7 receptors are expressed in the trigeminal ganglia but this expression is not increased by the inflammation induced by carrageenan in the TMJ region. The P2X7 receptor agonist BzATP induced TMJ inflammatory hyperalgesia that was significantly reduced by pretreatment with dexamethasone. These results indicate that P2X3 and P2X2/3 but not P2X7 receptors are involved in carrageenan-induced TMJ inflammatory hyperalgesia. However, functional P2X7 receptors are expressed in the TMJ region. The activation of these receptors by BzATP sensitizes the primary afferent nociceptors in the TMJ through the previous release of inflammatory mediators. The findings of this study point out P2X3 and P2X2/3 receptors, but not P2X7 receptors, as potential targets for the development of new analgesic drugs to control TMJ inflammatory pain.

Topics: Adenosine Triphosphate; Animals; Carrageenan; Hyperalgesia; Inflammation; Male; Purinergic P2X Receptor Agonists; Purinergic P2X Receptor Antagonists; Pyridines; Rats; Rats, Wistar; Receptors, Purinergic P2; Receptors, Purinergic P2X2; Receptors, Purinergic P2X3; Receptors, Purinergic P2X7; RNA, Messenger; Temporomandibular Joint; Tetrazoles; Trigeminal Ganglion

Activation of P2X3,2/3 receptors by endogenous ATP contributes to the development of inflammatory hyperalgesia. Given the clinical importance of mechanical hyperalgesia in inflammatory states, we hypothesized that the activation of P2X3,2/3 receptors by endogenous ATP contributes to carrageenan-induced mechanical hyperalgesia and that this contribution is mediated by an indirect and/or a direct sensitization of the primary afferent nociceptors. Co-administration of the selective P2X3,2/3 receptors antagonist A-317491, or the non-selective P2X3 receptor antagonist, TNP-ATP, with carrageenan blocked the mechanical hyperalgesia induced by carrageenan, and significantly reduced the increased concentration of tumor necrosis factor alpha (TNF-alpha) and chemokine-induced chemoattractant-1 (CINC-1) but not of interleukin-1 beta (IL-1 beta) induced by carrageenan. Co-administration of the selective P2X3,2/3 receptors antagonist A-317491 with carrageenan did not affect the neutrophil migration induced by carrageenan. Intrathecal administration of oligonucleotides antisense against P2X3 receptors for seven days significantly reduced the expression of P2X3 receptors in the saphenous nerve and significantly reduced the mechanical hyperalgesia induced by carrageenan. We concluded that the activation of P2X3,2/3 receptors by endogenous ATP is essential to the development of the mechanical hyperalgesia induced by carrageenan. Furthermore, we showed that this essential role of P2X3,2/3 receptors in the development of carrageenan-induced mechanical hyperalgesia is mediated by an indirect sensitization of the primary afferent nociceptors dependent on the previous release of TNF-alpha and by a direct sensitization of the primary afferent nociceptors.

Topics: Adenosine Triphosphate; Analysis of Variance; Animals; Carrageenan; Cytokines; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Enzyme-Linked Immunosorbent Assay; Hyperalgesia; Inflammation; Male; Oligodeoxyribonucleotides, Antisense; Pain Measurement; Pain Threshold; Peroxidase; Phenols; Polycyclic Compounds; Polysaccharides; Purinergic P2 Receptor Antagonists; Rats; Rats, Wistar; Receptors, Purinergic P2; Receptors, Purinergic P2X2; Receptors, Purinergic P2X3; Time Factors

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.

Topics: Adenosine Triphosphate; Animals; Cell Count; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Freund's Adjuvant; Functional Laterality; Ganglia, Spinal; Immunohistochemistry; Inflammation; Male; Mitogen-Activated Protein Kinases; Neurofilament Proteins; Neurons; Phosphorylation; Physical Stimulation; Platelet Aggregation Inhibitors; Purinergic P2 Receptor Agonists; Purinergic P2 Receptor Antagonists; Pyridoxal Phosphate; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P2; Receptors, Purinergic P2X