Methadone analgesia in morphine-insensitive CXBK mice.
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.
The Cotzias Laboratory of Neuro-Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
A
A
Chang
D W
DW
Emmel
G C
GC
Rossi
G W
GW
Pasternak
D000698:Analgesia; D000701:Analgesics, Opioid; D000818:Animals; D004351:Drug Resistance; D008297:Male; D008691:Methadone; D051379:Mice; D009020:Morphine
D000701:Analgesics, Opioid; D009020:Morphine; D008691:Methadone