title: Pain.
mesh_terms: D000818:Animals; D001921:Brain / Q000503:physiopathology; D004723:Endorphins / Q000502:physiology*; D004745:Enkephalins / Q000502:physiology*; D006801:Humans; D010146:Pain / Q000503:physiopathology*; D013373:Substance P / Q000502:physiology
chemical_list: D004723:Endorphins; D004745:Enkephalins; D013373:Substance P