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