title: Opioid Peptides: introduction.
mesh_terms: D000818:Animals; D004723:Endorphins / Q000502:physiology*; D006168:Guinea Pigs; D051381:Rats; D011957:Receptors, Opioid / Q000502:physiology; D009626:Terminology as Topic
chemical_list: D004723:Endorphins; D011957:Receptors, Opioid