Orphanin FQ is a functional anti-opioid peptide

Neuroscience. 1996 Nov;75(2):333-7. doi: 10.1016/0306-4522(96)00338-7.


The heptadecapeptide orphanin FQ has recently been shown to be the endogenous agonist for the orphan opioid-like receptor, LC132. The molecular evidence that LC132 and orphanin FQ are evolutionarily related to other opioid receptors and their ligands suggests that these proteins may also play a role in modulating opiate actions. We now report that orphanin FQ (0.5-10 nmol), injected intracerebroventricularly in mice, does not produce hyperalgesia as suggested previously but rather reverses opioid-mediated (i.e. naloxone-sensitive) stress-induced antinociception in three different algesiometric assays. In addition to its antagonism of endogenous opioid antinociception, orphanin FQ dose-dependently (2.5-25 nmol) reverses systemic morphine antinociception (5 mg/kg, s.c.). Based on these data, we propose that orphanin FQ is a functional anti-opioid peptide.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetates
  • Analgesics, Opioid / antagonists & inhibitors
  • Analgesics, Opioid / pharmacology
  • Animals
  • Dose-Response Relationship, Drug
  • Female
  • Hyperalgesia / chemically induced
  • Injections, Intraventricular
  • Male
  • Mice
  • Morphine / antagonists & inhibitors
  • Morphine / pharmacology
  • Narcotic Antagonists*
  • Opioid Peptides / administration & dosage
  • Opioid Peptides / pharmacology*
  • Pain Measurement
  • Stress, Psychological / complications


  • Acetates
  • Analgesics, Opioid
  • Narcotic Antagonists
  • Opioid Peptides
  • Morphine
  • nociceptin