G-protein coupled opioid receptor that functions as receptor for the endogenous neuropeptide nociceptin. Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of down-stream effectors. Signaling via G proteins mediates inhibition of adenylate cyclase activity and calcium channel activity. Arrestins modulate signaling via G proteins and mediate the activation of alternative signaling pathways that lead to the activation of MAP kinases. Plays a role in modulating nociception and the perception of pain. Plays a role in the regulation of locomotor activity by the neuropeptide nociceptin.