Distinct effect of intracerebroventricular and intrathecal injections of nociceptin/orphanin FQ in the rat formalin test.
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.
Wang
J L
JL
State Key Laboratory of Medical Neurobiology, Department of Neurobiology, Shanghai Medical University, People's Republic of China.
Zhu
C B
CB
Cao
X D
XD
Wu
G C
GC
D000595:Amino Acid Sequence; D000698:Analgesia; D000818:Animals; D005557:Formaldehyde / Q000494:pharmacology*; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008297:Male; D008969:Molecular Sequence Data; D018847:Opioid Peptides / Q000008:administration & dosage / Q000494:pharmacology*; D010146:Pain; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000378:metabolism*; D000097629:Nociceptin
D005557:Formaldehyde; D018847:Opioid Peptides; D011957:Receptors, Opioid; D000097629:Nociceptin