Dissociation of morphine-induced potentiation of turning and striatal dopamine release by amphetamine in the nigrally-lesioned rat.
Morphine has been reported to increase extracellular levels of dopamine in the brain of intact rats and to potentiate turning induced by amphetamine in nigrally-lesioned rats. The present study tested the hypothesis that there is a causal relationship between these two effects of morphine. We tested morphine alone, amphetamine alone, and the combination in separate groups of nigrally-lesioned rats for effects on turning and, by microdialysis, on extracellular dopamine levels. Morphine (3.0 or 10 mg/kg) did not produce significant turning but amphetamine (1.0 mg/kg) did. The lower dose, but not the higher dose, of morphine potentiated amphetamine-induced turning. Amphetamine, but not morphine, produced increases in extracellular dopamine levels. In contrast to what occurred with turning, 10 mg/kg but not 3.0 mg/kg morphine potentiated amphetamine-induced increases in extracellular dopamine levels. These results show that the potentiation of amphetamine-induced turning by morphine in nigrally-lesioned rats is not due to the potentiation of dopamine release in the intact striatum.
Kimmel
H L
HL
Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA.
Justice
J B
JB
Holtzman
S G
SG
D000661:Amphetamine / Q000494:pharmacology*; D000818:Animals; D004298:Dopamine / Q000378:metabolism*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D006892:Hydroxydopamines / Q000494:pharmacology; D008297:Male; D017551:Microdialysis; D009020:Morphine / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D017072:Neostriatum / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013239:Stereotyped Behavior / Q000187:drug effects*; D013378:Substantia Nigra / Q000187:drug effects / Q000378:metabolism*; D013565:Sympatholytics / Q000494:pharmacology
D018765:Dopamine Uptake Inhibitors; D006892:Hydroxydopamines; D009294:Narcotics; D013565:Sympatholytics; D009020:Morphine; D000661:Amphetamine; D004298:Dopamine