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Characterization of nociceptin/orphanin FQ-induced pain responses by the novel receptor antagonist N-(4-amino-2-methylquinolin-6-yl)-2-(4-ethylphenoxymethyl) benzamide monohydrochloride.

Abstract
At the spinal level, nociceptin/orphanin FQ (Noc/OFQ) produces pronociceptive and allodynic effects at low doses (picogram range), while causing antinociceptive effects at high doses (microgram range). The discrepancy of pain modulation by Noc/OFQ at low and high doses raised a question whether Noc/OFQ exerted actions through the same Noc/OFQ receptor. In the present study, we examined the involvement of the Noc/OFQ receptor in pain responses with the novel nonpeptide antagonist N-(4-amino-2-methylquinolin-6-yl)-2-(4-ethylphenoxymethyl) benzamide monohydrochloride (JTC-801). Allodynia and hyperalgesia evoked by intrathecal administration of Noc/OFQ (50 pg/mouse) were dose dependently blocked by simultaneous administration of JTC-801 with IC(50) values of 32.2 and 363 pg, respectively. JTC-801 did not induce allodynia by itself. Subcutaneous injection of formalin into a hindpaw evoked biphasic pain behaviors such as flinching and biting in mice. Noc/OFQ at 10 pg increased the second-phase pain behaviors evoked by 1% formalin, whereas it strongly inhibited both the first-phase and second-phase pain evoked by 2% formalin at 1 microg. Although the pronociceptive effect by 10 pg of Noc/OFQ was dose dependently blocked by JTC-801 with an IC(50) value of 4.58 pg, the antinociceptive effects by 1 microg of Noc/OFQ were not antagonized by JTC-801. Furthermore, both phases of 2% formalin-induced pain behaviors were relieved by JTC-801. These results demonstrate that pronociceptive responses induced by a low dose of Noc/OFQ may be mediated through the Noc/OFQ receptor in the spinal cord and that JTC-801 can be a useful antagonist to examine the involvement of endogenous Noc/OFQ and mediation of the Noc/OFQ receptor under physiological and pathophysiological conditions including pain.
AuthorsTadatoshi Muratani, Toshiaki Minami, Utako Enomoto, Masato Sakai, Emiko Okuda-Ashitaka, Kimihiro Kiyokane, Hidemaro Mori, Seiji Ito
JournalThe Journal of pharmacology and experimental therapeutics (J Pharmacol Exp Ther) Vol. 303 Issue 1 Pg. 424-30 (Oct 2002) ISSN: 0022-3565 [Print] United States
PMID12235279 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References
  • Aminoquinolines
  • Benzamides
  • N-(4-amino-2-methylquinolin-6-yl)-2-(4-ethylphenoxymethyl)benzamide
  • Narcotic Antagonists
  • Opioid Peptides
  • Receptors, Opioid
  • nociceptin
  • Nociceptin Receptor
  • Oprl1 protein, mouse
Topics
  • Aminoquinolines (administration & dosage, pharmacology)
  • Animals
  • Benzamides (administration & dosage, pharmacology)
  • Hyperalgesia (chemically induced)
  • Injections, Spinal
  • Kinetics
  • Male
  • Mice
  • Mice, Inbred Strains
  • Narcotic Antagonists
  • Opioid Peptides (administration & dosage, antagonists & inhibitors, pharmacology)
  • Pain (chemically induced, physiopathology)
  • Receptors, Opioid (physiology)
  • Nociceptin Receptor

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