Nociceptin/orphanin FQ (N/OFQ), a 17 amino acid peptide, is the endogenous agonist of the nociceptin/orphanin FQ peptide (NOP) receptor (previously termed ORL1 receptor) which belongs to the class A (Rhodopsin-like) γ subfamily of G protein-coupled receptors (GPCRs). Like all members the receptor has a common seven-transmembrane helical structure and is coupled predominantly to heterotrimeric Gi/Go proteins. N/OFQ receptor shows a high degree of structural homology with the μ-, δ- and κ-opioid receptors1. The intracellular events triggered by the binding of N/OFQ with the NOP receptor include inhibition of adenylyl cyclase, activation of phospholipase C (PLC) and of K+ channels, inhibition of Ca2+ channels, and activation of mitogen-activated protein-kinases (MAPKs). In neural tissues, the main effect is the inhibition of the release of neurotransmitters (acetylcholine, catecholamines, GABA, glutamate, 5-hydroxytryptamine, tachykinines