Dopaminergic mechanisms of opiate actions in brain.
We have studied the interactions between morphine and a dopamine-blocking agent (haloperidol) and a dopamine precursor, L-3,4-dihydroxyphenylalanine (L-dopa). We found that haloperidol potentiated morphine-induced analgesia and enhanced morphine tolerance. Morphine-tolerant mice exhibited enhanced sensitivity to the locomotor excitatory actions of L-dopa. We propose that morphine exerts some of its central nervous actions by first interfering with dopamine-mediated synaptic transmission and then initiating compensatory changes that superficially resemble denervation supersensitivity. These compensatory changes may underlie the excitatory actions of morphine.
D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D004298:Dopamine / Q000502:physiology*; D004357:Drug Synergism; D004361:Drug Tolerance; D006220:Haloperidol / Q000494:pharmacology; D006801:Humans; D007980:Levodopa / Q000494:pharmacology; D008297:Male; D051379:Mice; D009020:Morphine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009021:Morphine Dependence / Q000503:physiopathology; D009043:Motor Activity / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D011930:Reaction Time / Q000187:drug effects; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects
D000700:Analgesics; D009270:Naloxone; D007980:Levodopa; D009020:Morphine; D006220:Haloperidol; D004298:Dopamine