Antagonism of the response rate-decreasing effects of meperidine and morphine by beta-funaltrexamine and naltrexone in squirrel monkeys.
Level pressing by squirrel monkeys was maintained under a fixed-ratio 30 schedule of food presentation. The response rate-decreasing effects of meperidine and morphine were examined alone and in combination with several doses of the irreversible, mu-selective opioid antagonist beta-funaltrexamine and the reversible, opioid antagonist naltrexone. beta-Funaltrexamine alone decreased response rates to greater than 50% of control at all doses in two of the four monkeys and at the highest dose in one monkey. In the monkeys in which beta-funaltrexamine decreased rates, beta-funaltrexamine either did not shift the meperidine or the morphine dose-effect curve or it shifted these curves to the left. In the monkeys in which beta-funaltrexamine alone did not decrease rates, it shifted the meperidine and the morphine dose-effect curves to the right. Naltrexone also shifted both the meperidine and morphine dose-effect curves rightward, although not in a dose-dependent manner. These data suggest that the rate-decreasing effects of meperidine and morphine in squirrel monkeys are altered by beta-funaltrexamine and naltrexone in a similar manner, providing additional evidence that the rate-decreasing effects of both meperidine and morphine are mediated by mu-opioid receptors.
Hughes
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Department of Psychology, University of North Carolina, Chapel Hill 27599-3270, USA. chughes@gibbs.oit.unc.edu
Dykstra
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D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005247:Feeding Behavior / Q000187:drug effects* / Q000502:physiology; D008137:Longitudinal Studies; D008297:Male; D008614:Meperidine / Q000494:pharmacology*; D009020:Morphine / Q000494:pharmacology*; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D012054:Reinforcement, Psychology; D012453:Saimiri
D009292:Narcotic Antagonists; D009271:Naltrexone; D009020:Morphine; D008614:Meperidine