title: Differential antinociception by morphine and methadone in two sub-strains of Sprague-Dawley rats and its potentiation by dextromethorphan.
abstract: The antinociceptive effect of morphine and methadone was tested in two substrains of Sprague-Dawley (SD) rats, from B&K Universal, Sweden (BK) and Mollegård, Denmark (DK). In both sub-strains of SD rats subcutaneous morphine or methadone produced dose-dependent antinociception on the hot plate test. However, the effect of the opioids was less in DK-SD than BK-SD rats, particularly for morphine as it failed to produce maximal antinociception even at high doses. Dextromethorphan, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, potentiated the antinociceptive effect of morphine and methadone in the DK-SD rats. The potentiation of morphine by dextromethorphan was significantly greater than its effect on methadone at equipotent doses. The results showed that there is a sub-strain difference for SD rats in the response to the antinociceptive effect of opioids, which may be due to greater NMDA receptor activity in DK-SD than in BK-SD rats. The higher efficacy of methadone may be derived from its proposed NMDA receptor blocking property and/or high intrinsic activity.
authors.affiliation: Department of Medical Laboratory Sciences and Technology, Division of Clinical Neurophysiology, Karolinska Institutet, Huddinge University Hospital, Huddinge, SE-141 86 Stockholm, Sweden.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Bulka
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Wiesenfeld-Hallin
authors.forename: Xiao Jun
authors.initials: XJ
authors.lastname: Xu
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D002375:Catalepsy / Q000139:chemically induced / Q000503:physiopathology; D002490:Central Nervous System / Q000187:drug effects* / Q000378:metabolism; D003915:Dextromethorphan / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions / Q000502:physiology; D004361:Drug Tolerance / Q000502:physiology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D008297:Male; D008691:Methadone / Q000494:pharmacology*; D009020:Morphine / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009619:Nociceptors / Q000187:drug effects* / Q000378:metabolism; D010146:Pain / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism
chemical_list: D000701:Analgesics, Opioid; D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D011957:Receptors, Opioid; D003915:Dextromethorphan; D009020:Morphine; D008691:Methadone