Orphanin FQ antagonizes the analgesic effect of 5-HT in rat brain

Orphanin FQ (OFQ) is a new modulatory peptide which was found in 1994. It mediates in morphine analgesia and electroacupuncture analgesia. The interaction between OFQ and 5-hydroxytryptamine (5-HT) on analgesia was observed using the method of intracerebroventricular microinjection. The results showed that cumulative i. c. v. administration of gradually increasing doses of 5-HT produced a dose-dependent analgesia, and administration of different doses of OFQ separateness had no significant effect on tail flick latency, but 1 or 10 μg OFQ could reverse the analgesia induced by 5-HT, suggesting that OFQ could antagonize the analgesia induced by 5-HT in rat brain.