Interacts specifically with a number of opioid ligands. Receptor for neuropeptides B and W, which may be involved in neuroendocrine system regulation, food intake and the organization of other signals. Has a higher affinity for neuropeptide B. Found in cerebellum and frontal cortex. Detected at high levels in hippocampus, amygdala and trachea; at moderate levels in fetal brain, pituitary gland and prostate. Not in caudate, accumbens, kidney or liver. Also detected at high levels in lung carcinoma. Belongs to the G-protein coupled receptor 1 family.