The publication of the δ opioid receptor sequence led to the cloning of three homologous receptors: the μ and κ opioid receptors, and a novel opioid-like orphan receptor. The orphan receptor's endogenous ligand, a 17- amino-acid peptide that resembles dynorphin, was named 'orphanin FQ' and 'nociceptin' (OFQ/N(1-17)). The OFQ/N(1-17) receptor is expressed widely in the nervous system, and it is becoming clear that the peptide is likely to participate in a broad range of physiological and behavioral functions. At the cellular level, OFQ/N(1-17) has much in common with the classical opioids; however, functional studies are now revealing distinct actions of this peptide. Identified only two years ago, OFQ/N(1-17) has already attracted a great deal of attention. The number and diversity of papers focused on OFQ/N(1-17) at the recent meeting of the Society for Neuroscience augur an exciting future for this new peptide.
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