ABSTRACT
OBJECTIVE AND DESIGN: The aim was to investigate the signaling mechanisms and regulation of bradykinin (BK)-induced inflammation in rat knee joint. MATERIALS AND METHODS: Knee joints of anesthetized rats were perfused with BK (0.1-1.0 microM), and synovial plasma extravasation (PE) was evaluated by spectrophotometrical measurement of Evans Blue leakage. To examine the signaling pathway, B1 antagonist [des-Arg10]-HOE140 (0.1-1.0 microM) and B2 antagonist HOE140 (0.05-1.0 microM), calcitonin gene-related peptide (CGRP) antagonist CGRP8-37 (0.5-1.0 microM), prostaglandin E2 antagonist AH-6809 (0.1-1.0 microM), and histamine H1 antagonist mepyramine (0.1-1.0 microM) were used. Nociceptin (0.0001-1.0 microM) and antagonist J-113397 were tested for modulation of BK-induced PE. The analyses were compared side-by-side with 5-hydroxytryptamine-induced PE. RESULTS: BK perfusion dose-dependently induced PE, which was blocked by HOE140, CGRP8-37, AH-6809, and mepyramine. It was also inhibited by nociceptin, which could be reversed by antagonist J-113397. In contrast, 5-hydroxytryptamine-induced PE was biphasically regulated by nociceptin and was not antagonized by CGRP8-37. CONCLUSIONS: BK-induced PE is mediated by B2 receptors and may involve CGRP, prostaglandin, and histamine pathways. BK-induced PE is inhibited by nociceptin through the activation of ORL1 receptors. There are differences between BK- and 5-hydroxytryptamine-induced inflammation in signaling and modulation.
Subject(s)
Bradykinin/metabolism , Knee Joint/metabolism , Opioid Peptides/metabolism , Plasma/metabolism , Receptor, Bradykinin B1/metabolism , Receptor, Bradykinin B2/metabolism , Animals , Bradykinin B1 Receptor Antagonists , Bradykinin B2 Receptor Antagonists , Calcitonin Gene-Related Peptide/metabolism , Coloring Agents/metabolism , Dinoprostone/antagonists & inhibitors , Dinoprostone/metabolism , Evans Blue/metabolism , Histamine/metabolism , Humans , Male , Rats , Rats, Sprague-Dawley , Serotonin/metabolism , Signal Transduction/physiology , NociceptinABSTRACT
The purpose of this study was to determine whether the 5-hydroxytryptamine7 (5-HT7) receptor is expressed by nociceptor-like neurons in the rat PNS and whether 5-HT activates these nociceptors via the 5-HT7 receptor subtype. Using a polyclonal antibody and the method of immunofluorescence staining, we demonstrated that the 5-HT7 receptor appears predominately on "nociceptor-like" neurons of the rat lumbar dorsal root ganglia. Using immunocytochemical methods, we showed that the immunoreactivity of the 5-HT7 receptor antibody complex is localized in the superficial layers of the spinal cord dorsal horn, which corresponds with laminae I, IIouter and IIinner. Furthermore, we demonstrated that noxious stimulation produced by knee injection of 5-HT or a 5-HT7 agonist dose-dependently increases c-Fos production of the rat spinal cord dorsal horn. This effect was significantly inhibited by the preinjection of a 5-HT7 antagonist. We conclude that the 5-HT7 receptor is expressed by rat primary afferent nociceptors which terminate in the superficial layers of the spinal cord dorsal horn and that the 5-HT7 receptor subtype is involved in nociceptor activation by 5-HT.
Subject(s)
Posterior Horn Cells/drug effects , Posterior Horn Cells/metabolism , Receptors, Serotonin/metabolism , Serotonin/pharmacology , 8-Hydroxy-2-(di-n-propylamino)tetralin/pharmacology , Animals , Dose-Response Relationship, Drug , Fluorescent Antibody Technique, Indirect , Injections, Intra-Articular , Knee Joint , Lumbosacral Region , Male , Methiothepin/pharmacology , Microscopy, Fluorescence , Posterior Horn Cells/cytology , Proto-Oncogene Proteins c-fos/metabolism , Rats , Rats, Sprague-Dawley , Receptors, Serotonin/analysis , Serotonin/administration & dosage , Serotonin Antagonists/pharmacology , Serotonin Receptor Agonists/pharmacologyABSTRACT
The present study investigates the involvement of opioid receptors in the antinociceptive effects of nociceptin in the spinal cord of the rat. Intrathecal administrations of 5 and 10 nmol of nociceptin significantly increase the withdraw response latencies to noxious thermal and mechanical stimulations. This nociceptin-induced antinociceptive effect is significantly attenuated by intrathecal injection of (Nphe(1))nociceptin(1-13)-NH(2), a selective antagonist of the nociceptin receptor (opioid receptor-like receptor ORL1), indicating an ORL1 receptor-mediated mechanism. This antinociceptive effect is also significantly attenuated by intrathecal injections of naloxone (a nonselective opioid receptor antagonist), naltrindole (a selective delta-opioid receptor antagonist), and beta-funaltrexamine (a selective mu-opioid receptor antagonist) in a dose-dependent manner, but not by the selective kappa-opioid receptor antagonist norbinaltorphimine. Since it is unlikely that nociceptin acts by direct binding to opioid receptors, these results suggest a possible interaction between the nociceptin/ORL1 and opioid systems in the dorsal horn of the rat spinal cord.
