title: Endogenous opioid systems in brain.
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology; D001923:Brain Chemistry; D004723:Endorphins / Q000032:analysis / Q000502:physiology*; D004745:Enkephalins / Q000032:analysis / Q000502:physiology; D006801:Humans; D010146:Pain / Q000503:physiopathology; D011957:Receptors, Opioid / Q000502:physiology*
chemical_list: D004723:Endorphins; D004745:Enkephalins; D011957:Receptors, Opioid