Nociceptin or orphanin FQ, a 17 amino acid neuropeptide, is the endogenous ligand for the nociceptin receptor (NOP, ORL-1). Nociceptin is an opioid-related peptide, but it does not act at the classic opioid receptors and its actions are not antagonized by the opioid antagonist naloxone. Nociceptin is a potent anti-analgesic. Nociceptin is widely distributed in the CNS; it is found in many regions of the hypothalamus, brainstem, and forebrain, as well as in the ventral horn and dorsal horn of the spinal cord. Nociceptin acts at the Nociceptin receptor (NOP1), formerly known as ORL-1. The receptor is also widely distributed in the brain, including in the cortex, anterior olfactory nucleus, lateral septum, hypothalamus, hippocampus, amygdala, central gray, pontine nuclei, interpeduncular nucleus, substantia nigra, raphe complex, locus coeruleus, and spinal cord.
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