Multiple opioid receptors: a little about their history and some implications related to evolution.
D000818:Animals; D005075:Biological Evolution; D006801:Humans; D009020:Morphine / Q000494:pharmacology; D009269:Nalorphine / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*; D013329:Structure-Activity Relationship
D009294:Narcotics; D011957:Receptors, Opioid; D009020:Morphine; D009269:Nalorphine