Behavioral Effects of a Synthetic Agonist Selective for Nociceptin/Orphanin FQ Peptide Receptors in Monkeys

Mei Chuan Ko, James H. Woods, William E. Fantegrossi, Chad M. Galuska, Jürgen Wichmann, Eric P. Prinssen

Research output: Contribution to journalArticlepeer-review

85 Scopus citations


Behavioral effects of a nonpeptidic NOP (nociceptin/orphanin FQ Peptide) receptor agonist, Ro 64-6198, have not been studied in primate species. The aim of the study was to verify the receptor mechanism underlying the behavioral effects of Ro 64-6198 and to systematically compare behavioral effects of Ro 64-6198 with those of a -opioid receptor agonist, alfentanil, in monkeys. Both Ro 64-6198 (0.001-0.06 mg/kg, s.c.) and alfentanil (0.001-0.06 mg/kg, s.c.) produced antinociception against an acute noxious stimulus (50°C water) and capsaicin-induced allodynia. An NOP receptor antagonist, J-113397 (0.01-0.1 mg/kg, s.c.), dose-dependently produced rightward shifts of the dose-response curve of Ro 64-6198-induced antinociception. The apparent pA 2 value of J-113397 was 8.0. Antagonist studies using J-113397 and naltrexone revealed that Ro 64-6198 produced NOP receptor-mediated antinociception independent of -opioid receptors. In addition, alfentanil dose-dependently produced respiratory depression and itch/scratching responses, but antinociceptive doses of Ro 64-6198 did not produce such effects. More important, Ro 64-6198 did not produce reinforcing effects comparable with those of alfentanil, cocaine, or methohexital under self-administration procedures in monkeys. These results provide the first functional evidence that the activation of NOP receptors produces antinociception without reinforcing effects in primates. Non-peptidic NOP receptor agonists may have therapeutic value as novel analgesics without abuse liability in humans.

Original languageEnglish (US)
Pages (from-to)2088-2096
Number of pages9
Issue number9
StatePublished - Aug 2009
Externally publishedYes


  • Abuse liability
  • Analgesic
  • Antinociception
  • Opioid
  • Self-administration

ASJC Scopus subject areas

  • Pharmacology
  • Psychiatry and Mental health


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