RECENT studies suggest that the novel opioid peptide orphanin FQ (OFQ) is involved in pain modulation. We found that intracerebroventricular (i.c.v.) administration of OFQ in the rat produced a dose-dependent antagonism of the analgesia induced by 100 Hz electroacupuncture (EA) stimulation as measured in the radiant heat tail-flick assay. Antisense oligonucleotides injected i.c.v. potentiated EA analgesia, presumably by interfering with the expression of the OFQ receptor in brain. These results suggest that endogenous OFQ exerts a tonic antagonistic effect on EA-induced analgesia. No such antagonism was observed when OFQ was injected intrathecally (i.t.). Rather, it appears that spinal OFQ produced a marked analgesic effect and enhanced EA-induced analgesia. These findings are consistent with the experimental results obtained in rats where morphine-induced analgesia is antagonized by i.c.v. OFQ and potentiated by i.t. OFQ.
1Neuroscience Research Center, Beijing Medical University, Beijing 100083, PR China
2Oregon Health Sciences University, Portland, OR 97201
3Department of Psychology, University of Illinois, Urbana, IL 61801
4Vollum Institute for Advanced Biomedical Research, Portland, OR 97201, USA
5Corresponding Author: Ji-Sheng Han.
ACKNOWLEDGEMENTS: We would like to thank Drs Mary M. Heinricher and John K. Belknap for their helpful comments on this manuscript. This work was supported by NIAAA (J.E.G.), NIDA (J.-S.H. and D.K.G.), NINDS (J.S.M.) and the Markey Charitable Trust (D.K.G.).
Received 30 August 1996; accepted 17 October 1996