The History of N/OFQ and the NOP Receptor

The discovery of nociceptin/orphanin FQ (N/OFQ) marks the genuine start of the reverse pharmacology era, when systematic hunting for ligands of orphan receptors began. The choice of this particular target was no coincidence as the orphan receptor ORL-1 displayed high similarity to known opioid receptors, and thus its elusive ligand held promise to find more than a ligand but a missing opioid peptide. N/OFQ indeed turned out to belong to the opioid peptide family, but with significant pharmacological and functional distinctions. The quest for understanding N/OFQ's physiological functions has produced some novel insights into stress regulation and many other body functions but is still ongoing almost 25 years after its discovery. This chapter highlights the early steps of orphan receptor research and some of the protagonists who helped to advance the field.