title: Spinal and supraspinal opioid analgesia in the mouse: the role of subpopulations of opioid binding sites.
abstract: The selective in vivo blockade of high affinity (mu1) opioid binding sites in mice by naloxazone reduced the analgesic potency of opiates and opioid peptides, evidenced by a shift of their analgesic ED50 values. However, the extent of these shifts varied significantly between a series of opioid drugs, ranging from 12-fold for morphine to 4-fold for D-Ala2-D-Leu5-enkephalin. These findings suggested that analgesia in naloxazone-treated animals is mediated through a different subpopulation of receptors than in normal controls. Correlating these analgesic shifts for a series of opioids with their affinity for different [3H]opioid binding sites suggested an analgesic role for delta sites. Additional studies in mice with spinal transections suggested that mu1 analgesia was primarily supraspinal.
mesh_terms: D000698:Analgesia; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000502:physiology*; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D008815:Mice, Inbred Strains; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000031:analogs & derivatives* / Q000494:pharmacology; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*
chemical_list: D011957:Receptors, Opioid; D009270:Naloxone; D004744:Enkephalin, Methionine; C024224:naloxazone; D009020:Morphine; C028208:metkephamid