title: Modulation of opioid system in C57 mice after repeated treatment with morphine and naloxone: biochemical and behavioral correlates.
abstract: C57 BL/6J (C57) mice display a particular pattern of responses following morphine administration, such as a rapid development of tolerance to the pharmacological action of the opiate and an increase in locomotor activity after a single injection of the drug. We have measured met-enkephalin content and the responsiveness of different opiate receptors after repeated administration of morphine and naloxone. Prolonged morphine administration changes neither met-enkephalin levels, nor the density of the opiate receptors in mice brain. In contrast repeated administration of the opiate antagonist naloxone, produced a marked increase in the number of 3H- DHM and 3H- DADLE binding sites in striatum and brainstem without modifying met-enkephalin concentrations. Behavioral studies have indicated that the morphine-induced increase in locomotor activity is enhanced in naloxone pretreated mice, thus suggesting a possible correlation between the behavioral response to morphine in C57 mice and the higher number of opiate receptors in the striatum.
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D001933:Brain Stem / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism; D004744:Enkephalin, Methionine / Q000378:metabolism; D007700:Kinetics; D008124:Locomotion / Q000187:drug effects; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D011869:Radioligand Assay; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism*
chemical_list: D011957:Receptors, Opioid; D009270:Naloxone; D004744:Enkephalin, Methionine; D009020:Morphine