title: Thrombin inhibits NMDA-mediated nociceptive activity in the mouse: possible mediation by endothelin.
abstract: The CNS expresses many components of an extracellular protease signalling system, including the protease-activated receptor-1 (PAR-1) whose tethered ligand is generated by thrombin. Activation of PAR-1 potentiates NMDA receptor activity in hippocampal neurons. Because NMDA activity mediates hyperalgesia, we tested the hypothesis that PAR-1 receptors also regulate pain processing. In contrast to the potentiating effect of thrombin in the hippocampus, NMDA-induced behaviours and the transient mechanical hyperalgesia (von Frey fibres) induced by intrathecally injected NMDA in mice were inhibited by thrombin in a dose-related fashion. This anti-hyperalgesic effect was mimicked by SFLLRN, the natural ligand at PAR-1 binding sites, but not SLIGRL-amide, a PAR-2 agonist. The effects of SFLLRN were less potent and shorter in duration than that of thrombin, consistent with its more transient effect on PAR-1 sites. Both thrombin and SFLLRN inhibited acetic acid-induced abdominal stretch (writhing) behaviours, which were also sensitive to NMDA antagonism, but not hot plate or tail flick latencies, which were insensitive to NMDA antagonists. TFLLR-amide, a selective ligand for PAR-1 sites, mimicked the effects of thrombin while RLLFT-amide, an inactive, reverse peptide sequence, did not. In addition, the effect of TFLLR-amide was prevented by RWJ-56110, a PAR-1 antagonist. Thrombin and TFLLR-amide produced no oedema (Evans Blue extravasation) in the spinal cord that would account for these effects. Based on the reported ability of thrombin to mobilize endothelin-1 from astrocytes, we tested the role of this compound in thrombin's activity. BQ123, an endothelin A receptor antagonist, prevented thrombin's inhibition of writhing and NMDA-induced behaviours while BQ788, an endothelin B receptor antagonist, did not. Thus, activation of PAR-1 sites by thrombin in the CNS appears to inhibit NMDA-mediated nociception by a pathway involving endothelin type A receptors.
authors.affiliation: University of Minnesota, Department of Veterinary Pathobiology, 1988 Fitch Avenue, St Paul, MN 55108, USA. larso011@umn.edu
authors.forename: Ming
authors.initials: M
authors.lastname: Fang
authors.forename: Katalin J
authors.initials: KJ
authors.lastname: Kovács
authors.forename: Lauralei L
authors.initials: LL
authors.lastname: Fisher
authors.forename: Alice A
authors.initials: AA
authors.lastname: Larson
mesh_terms: D019342:Acetic Acid; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002199:Capillary Permeability / Q000187:drug effects; D016232:Endothelins / Q000502:physiology*; D005070:Evans Blue; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006930:Hyperalgesia / Q000139:chemically induced; D007191:Indazoles / Q000494:pharmacology; D007274:Injections, Intraperitoneal; D008297:Male; D051379:Mice; D016202:N-Methylaspartate / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects*; D009842:Oligopeptides / Q000494:pharmacology; D010147:Pain Measurement / Q000187:drug effects; D010446:Peptide Fragments / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D010812:Physical Stimulation; D010880:Piperidines / Q000494:pharmacology; D011930:Reaction Time / Q000187:drug effects; D044022:Receptor, Endothelin A / Q000187:drug effects / Q000502:physiology; D044023:Receptor, Endothelin B / Q000187:drug effects / Q000502:physiology; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D014508:Urea / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D016232:Endothelins; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D007191:Indazoles; D009842:Oligopeptides; C462999:PAR-1-activating peptide; D010446:Peptide Fragments; D010456:Peptides, Cyclic; D010880:Piperidines; C435606:RWJ-56110; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; C082835:thrombin receptor peptide (42-47); C086539:BQ 788; D005070:Evans Blue; D016202:N-Methylaspartate; D014508:Urea; D013917:Thrombin; C040308:phenylalanyl-prolyl-arginine-chloromethyl ketone; D019342:Acetic Acid; C072247:cyclo(Trp-Asp-Pro-Val-Leu)