Distinct effect of intracerebroventricular and intrathecal injections of nociceptin/orphanin FQ in the rat formalin test

Regul Pept. 1999 Feb 5;79(2-3):159-63. doi: 10.1016/s0167-0115(98)00161-x.


Nociceptin/orphanin FQ (nociceptin/OFQ), a newly discovered heptadecapeptide has been regarded as an endogenous ligand for orphan opioid receptor. The present study was designed to investigate the effect of nociceptin/OFQ on pain response and opioid analgesia in the rat formalin test. The results showed that intracerebroventricular injection of 1 microg nociceptin/OFQ enhanced the pain response, and 0.1 or 0.5 microg nociceptin/OFQ had no effect on formalin-induced pain. When 0.1 or 1 microg nociceptin/OFQ were used together with mu-, delta-, or kappa-opioid receptor agonists, endomorphin-1, DSLET or U50488H, respectively, it attenuated mu- and kappa- but not delta-receptor mediated analgesia. On the other hand, intrathecal injection of nociceptin/OFQ (0.1, 1 and 5 microg) reduced the pain response in the formalin test. In conclusion, nociceptin/OFQ potentiated formalin-induced pain response and antagonized opioid analgesia in the rat brain but inhibited pain response in the spinal cord.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Analgesia
  • Animals
  • Formaldehyde / pharmacology*
  • Injections, Intraventricular
  • Injections, Spinal
  • Male
  • Molecular Sequence Data
  • Opioid Peptides / administration & dosage
  • Opioid Peptides / pharmacology*
  • Pain
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Opioid / metabolism*


  • Opioid Peptides
  • Receptors, Opioid
  • Formaldehyde
  • nociceptin