Despite its structural homology with opioid peptides, N/OFQ does not bind to the opioid receptors, and conversely, opioid peptides do not activate the NOPR (Reinscheid et al., 1996). Additionally, while opioid-like, N/OFQ elicits pro-nociceptive effects after intracranial administration, giving rise to the name nociceptin (Meunier et al., 1995), and acts in the brain to produce functional anti-opioid effects. It blocks opioid-induced supraspinal analgesia (Mogil et al., 1996), morphine-induced CPP (Ciccocioppo et al., 2000; Murphy et al., 1999) and morphine-induced increases in extracellular DA levels in the NAC (Di Giannuario and Pieretti, 2000).
