Supraspinal hyperalgesia and spinal analgesia by [Phe(1)psi(CH2-NH)Gly(2)]nociceptin-(1-13)-NH2 in rat

[Phe(1)psi(CH2-NH)Gly(2)]nociceptin-(1-13)-NH2, a pseudopeptide analog of n ociceptin, was originally seen as an antagonist of nociceptin receptors. In the present study, it was observed that intracerebroventricular (i.c.v.) i njection of this pseudopeptide (1, 5, 10 mu g) significantly decreased the tail-flick latency of rats, indicating a hyperalgesic effect, while intrath ecal (i.t.) injection of it (1, 2.5, 10 mu g) dramatically increased the ta il-flick latency, indicating an analgesic effect. This strengthened the in vivo evidence that [Phe(1)psi(CH2NH)Gly(2)]nociceptin-(1-13)-NH2 might be a n agonist of nociceptin receptors. (C) 1999 Elsevier Science B.V. All right s reserved.