Methadone analgesia in morphine-insensitive CXBK mice

Eur J Pharmacol. 1998 Jun 19;351(2):189-91. doi: 10.1016/s0014-2999(98)00366-5.


Methadone, a potent opioid analgesic, has long been considered a mu-opioid, based upon the similarities between its actions and those of morphine. This classification is supported by the sensitivity of methadone analgesia to the highly mu-opioid receptor-selective antagonist beta-funaltrexamine. Yet, CXBK mice respond normally to methadone despite their insensitivity to systemic morphine, distinguishing between the receptor mechanisms of the two drugs. Beta-funaltrexamine antagonizes methadone analgesia in CXBK mice, implying that the opioid is still acting through a mu-opioid receptor. These results reveal distinct analgesic mechanisms for morphine and methadone and provide further support for multiple subtypes of mu-opioid receptors.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Analgesia
  • Analgesics, Opioid*
  • Animals
  • Drug Resistance
  • Male
  • Methadone*
  • Mice
  • Morphine


  • Analgesics, Opioid
  • Morphine
  • Methadone