title: Multiple opioid systems and pain.
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D002490:Central Nervous System / Q000032:analysis*; D002908:Chronic Disease; D004723:Endorphins / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D010146:Pain / Q000503:physiopathology*; D059408:Pain Management; D010902:Pituitary Gland / Q000032:analysis; D051381:Rats; D011957:Receptors, Opioid / Q000378:metabolism / Q000502:physiology*; D013116:Spinal Cord / Q000032:analysis
chemical_list: D004723:Endorphins; D011957:Receptors, Opioid