Characterization of Nociceptin/Orphanin FQ-Induced Pain Responses by the Novel Receptor AntagonistN-(4-Amino-2-methylquinolin-6-yl)-2-(4-ethylphenoxymethyl) Benzamide Monohydrochloride

• Published in: The Journal of pharmacology and experimental therapeutics 2002-10, Vol.303 (1), p.424
• Main Authors: Tadatoshi Muratani, Toshiaki Minami, Utako Enomoto, Masato Sakai, Emiko Okuda-Ashitaka, Kimihiro Kiyokane, Hidemaro Mori, Seiji Ito
• Format: Article
• Language: eng ; jpn
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.102.036095

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 μg. 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 μg 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.