Effects of medial raphe and raphe magnus lesions on the analgesic activity of morphine and methadone.
The effects of lesions of the raphe nuclei on opiate-induced antinociception and brain serotonin (5-HT) levels were investigated. Lesions of the medial raphe nucleus effectively antagonized the analgesic effects of morphine, but not methadone, and lowered brain 5-HT. The decrement in analgesic activity of morphine was reversed by pretreatment with 5-hydroxytryptophan. Lesions of the raphe magnus, a descending 5-HT system, antagonized the analgesic potency of both morphine and methadone. These experiments indicate a differential effect of 5-HT manipulation on opiate-induced analgesia, suggesting a different mechanism of analgesic action for morphine and methadone.
D000700:Analgesics; D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects; D001933:Brain Stem / Q000502:physiology*; D008297:Male; D008691:Methadone / Q000494:pharmacology*; D009020:Morphine / Q000494:pharmacology*; D011903:Raphe Nuclei / Q000502:physiology*; D051381:Rats; D011930:Reaction Time / Q000187:drug effects; D012701:Serotonin / Q000378:metabolism; D013997:Time Factors
D000700:Analgesics; D012701:Serotonin; D009020:Morphine; D008691:Methadone