[Effect of orphanin FQ on acupuncture analgesia and noxious stimulation in the periaqueductal gray].

Orphanin FQ (OFQ) is a newly-discovered neuropeptide which shares great similar sequence with endogenous opioid peptide but with different functions. The present study was to investigate the role of OFQ microinjected in the periaqueductal gray (PAG) on pain threshold and acupuncture analgesia (AA) using tail flick tests. The results show that the hyperalgesia of OFQ and its antagonization on AA in PAG are dose-related. OFQ in PAG decreases the enhancing effect on AA induced by ohmefentanyl, a selective mu-receptor agonist. These observations suggest that OFQ in PAG can increase the rat pain sensitivity and antagonize AA.