Bidirectional modulatory effect of orphanin FQ on morphine-induced analgesia: Antagonism in brain and potentiation in spinal cord of the rat

Jin Hua Tian, Wei Xu, Yuan Fang, Jeffrey S. Mogil, Judith E. Grisel, David Grandy, Ji Sheng Han

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    1. The present study was designed to investigate further the effects of the newly discovered orphanin FQ (OFQ) - the endogenous ligand for the orphan opioid receptor (called, e.g., ORL1 and LC132) - on pain modulation in the rat. We used the tail-flick assay as a nociceptive index. 2. When injected into a cerebral ventricle, OFQ (4 fmol-10 nmol) has no effect on basal tail-flick latency by itself at any dose, but dose-dependently antagonizes systemic morphine analgesia (400 fmol-50 nmol). 3. Injected intrathecally, OFQ (3 and 10 nmol) displayed an analgesic effect without producing motor dysfunction, and potentiated morphine analgesia (1 and 10 nmol). 4. The anti-opioid effect of OFQ in rat brain and the high level of expression of LC132/ORL1 receptor in the locus coeruleus indicated a possible role of OFQ in the precipitation of opiate withdrawal symptoms. However, no such precipitation was observed by OFQ in morphine-dependent rats.

    Original languageEnglish (US)
    Pages (from-to)676-680
    Number of pages5
    JournalBritish Journal of Pharmacology
    Issue number4
    Publication statusPublished - 1997



    • Analgesia
    • Anti-opioid
    • Morphine withdrawal
    • ORL/LC132
    • Orphanin FQ/nociceptin

    ASJC Scopus subject areas

    • Pharmacology

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