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

[Phe¹ ψ(CH₂-NH)Gly²]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, [Phe¹ ψ(CH₂-NH)Gly²]nociceptin-(1-13)-NH₂ appears to have agonist activity after spinal administration. The noxious evoked activity of the neurones was inhibited by [Phe¹ ψ(CH₂-NH)Gly²]nociceptin-(1-13)-NH₂, which was as potent as nociceptin itself.