In vitro inhibitory effects of J-113397 on nociceptin/orphanin FQ-stimulated

J-113397 (1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one) is a recently developed antagonist of the opioid receptor-like 1 (ORL1) receptor. We compared the in vitro functional profile J-113397 on [35S]guanosine 5'-O-(gamma-thio)triphosphate (GTPgammaS) binding to mouse brain with that of [Phe1psi(CH2-NH)Gly2]nociceptin(1-13)NH2 and naloxone benzoylhydrazone (NalBzoH). J-113397 antagonized nociceptin/orphanin FQ-stimulated [35S]GTPgammaS binding to mouse brain with an IC50 value of 7.6 nM, but had no effect on basal [35S]GTPgammaS binding by itself. [Phe1psi(CH2-NH)Gly2]nociceptin(1-13)NH2 partially antagonized nociceptin/orphanin FQ-stimulated [35S]GTPgammaS binding but showed agonistic activity on ORL1 by itself. NalBzoH showed antagonistic activity on ORL1 receptor but had significant agonistic activity on other opioid receptors at lower doses. Schild plot analysis demonstrated competitive antagonism of J-113397 on ORL1 receptor in mouse brain. A [35S]GTPgammaS binding study using ORL1 receptor-deficient mice confirmed the selective antagonism of J-113397 on ORL1 receptor. These data indicate that J-113397 is the most potent and selective antagonist of ORL1 receptor in mouse brain that has yet been reported, and therefore will be a useful tool for characterization of ORL1 receptors in the brain.