Ligand of the opioid receptor-like receptor OPRL1. It may act as a transmitter in the brain by modulating nociceptive and locomotor behavior. May be involved in neuronal differentiation and development. Blocks nociceptin action in pain transmission by inhibiting nociceptin-induced hyperalgesia and allodynia. Has potent analgesic activity. Expressed predominantly in the spinal cord and brain, being more abundant in the hypothalamus and striatum. Also found in small amounts in ovary. Specific enzymatic cleavages at paired basic residues probably yield other active peptides besides nociceptin. The N-terminal domain contains 6 conserved cysteines thought to be involved in disulfide bonding and/or processing. Belongs to the opioid neuropeptide precursor family.