Possible involvement of mu 2-opioid receptor-mediated mechanisms in morphine-induced enhancement of the pentobarbital-induced loss of the righting reflex in the mouse.
The effects of pretreatment with selective mu-, delta- and kappa-opioid receptor antagonists on the enhancement of the pentobarbital-induced loss of the righting reflex by morphine were examined in mice. Mice injected with pentobarbital (50 mg/kg, i.p.) showed an increased duration for the loss of the righting reflex after administration of morphine. This enhancement of the pentobarbital-induced loss of the righting reflex produced by morphine (10 mg/kg, s.c.) was significantly antagonized by pretreatment with beta-funaltrexamine, a selective mu-opioid receptor antagonist, but not by pretreatment with naloxonazine, a selective mu 1-opioid receptor antagonist. Furthermore, neither naltrindole, a selective delta-opioid receptor antagonist, nor nor-binaltorphimine, a selective kappa-opioid receptor antagonist, had a significant effect on the enhancement of the pentobarbital-induced loss of the righting reflex by morphine. These results suggest that mu 2-, rather than mu 1-, delta- and kappa-, opioid receptor-mediated mechanisms are involved in the morphine-induced enhancement of the pentobarbital-induced loss of the righting reflex.
Kamei
J
J
Department of Pathophysiology and Therapeutics, Faculty of Pharmaceutical Sciences, Hoshi University, Tokyo, Japan.
Ohsawa
M
M
Nagase
H
H
D000818:Animals; D004357:Drug Synergism; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009020:Morphine / Q000494:pharmacology*; D010424:Pentobarbital / Q000494:pharmacology*; D004856:Postural Balance / Q000187:drug effects*; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000502:physiology*
D017450:Receptors, Opioid, mu; D009020:Morphine; D010424:Pentobarbital