Naloxone blocks the analgesic action of levorphanol but not of dextrorphan in the leopard frog

Craig W. Stevens, Paul D. Pezalla

Research output: Contribution to journalArticle

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Intraspinal injection of levorphanol (3 μg) at the lumbar area of the leopard frog, Rana pipiens, induced analgesia which was completely blocked by co-injection of naloxone (3 μg), whereas dextrorphan (3 μg) induced analgesia which was unaffected by naloxone. Subcutaneous levorphanol (20 or 80 mg/kg) induced a dose-dependent analgesia which was blocked by concurrent naloxone (2 mg/kg), while only the higher dose of dextrorphan (80 mg/kg) induced analgesia which was unaffected by concurrent naloxone at 8 or 80 mg/kg. These data are the first to indicate naloxone-insensitive, dextrorphan-induced analgesia.

Original languageEnglish
Pages (from-to)171-174
Number of pages4
JournalBrain Research
Issue number1
Publication statusPublished - 28 May 1984



  • amphibians
  • analgesia
  • dextrorphan
  • levorphanol
  • naloxone
  • μ-opiate receptor
  • σ-opiate receptor

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