Orphanin FQ/nociceptin: From neural circuitry to behavior

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42 Scopus citations


Orphanin FQ/nociceptin (OFQ/N), the endogenous ligand for the "orphan" opioid receptor ORL-1 (NOP1) was first identified in 1995. In the years since its discovery, a large body of evidence has accumulated showing that OFQ/N and its receptor are widely distributed in the nervous system, and showing that OFQ/N has potent and indiscriminate inhibitory actions on neurons in many regions. However, numerous studies investigating the functional role of OFQ/N in physiology or behavior have failed to provide a coherent view. Pain and analgesia have been the best studied, and administration of OFQ/N is reported to have no effect, to produce hyperalgesia, analgesia or anti-hyperalgesia. Effects of OFQ/N receptor antagonists have proved similarly contentious. In an attempt to resolve this controversy, we investigated the actions of OFQ/N on the activity of physiologically characterized neurons in the rostral ventromedial medulla, a region with a well-documented role in pain modulation(Heinricher et al., 1997). The results of those experiments demonstrate that this peptide is neither "anti-opioid" or "anti-hyperalgesic". It is simply inhibitory. For this reason, the effects seen in functional studies will only be fully understood when examined in the context of identified neural circuits.

Original languageEnglish (US)
Pages (from-to)813-822
Number of pages10
JournalLife Sciences
Issue number6
StatePublished - Jun 27 2003


  • "Anti-opioid"
  • Analgesia
  • Circuitry
  • Nociceptin
  • Orphanin FQ
  • Pain

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Pharmacology, Toxicology and Pharmaceutics(all)


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