INVOLVEMENT OF ENDOGENOUS ORPHANIN FQ IN ELECTROACUPUNCTURE-INDUCED ANALGESIA

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 a ntagonism of the analgesia induced by 100 Hz electroacupuncture (EA) s timulation 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. Thes e results suggest that endogenous OFQ exerts a tonic antagonistic effe ct on EA-induced analgesia. No such antagonism was observed when OFQ w as injected intrathecally (i.t.). Rather, it appears that spinal OFQ p roduced a marked analgesic effect and enhanced EA-induced analgesia. T hese findings are consistent with the experimental results obtained in rats where morphine-induced analgesia is antagonized by i.c.v. OFQ an d potentiated by i.t. OFQ.