Evidence that [Phe1 ψ (CH2-NH)Gly2]nociceptin-(1-13)-NH2, a peripheral ORL-1 receptor antagonist, acts as an agonist in the rat spinal cord

[Phe(1) psi(CH2-NH)Gly(2)]nociceptin-(1-13)-NH2, a pseudopeptide analogue of nociceptin is an antagonist in peripheral assays. Here, using in vivo electrophysiological recordings of dorsal horn neurones, [Phe(1) psi(CH2-NH)Gly(2)]nociceptin-(1-13)-NH2 appears to have agonist activity after spinal administration. The noxious evoked activity of the neurones was inhibited by [Phe(1) psi(CH2-NH)Gly(2)]nociceptin-(1-13)-NH2, which was as potent as nociceptin itself.