Potentiation of morphine-elicited circling by dopaminergic uptake blockade.
Contraversive circling induced by unilateral infusions of morphine (7.5 nanomoles or 5 micrograms) into the ventral tegmental area was studied under conditions of dopamine uptake inhibition. Dopamine uptake blockade with either nomifensine (2.5 mg/kg) or GBR 13069 (2.0 mg/kg) resulted in a 3-fold increase in the rate of circling. Naloxone (1.5 mg/kg) attenuated but did not completely block the potentiated circling. These data are consistent with the hypothesis that morphine causes contraversive circling through local activation or disinhibition of dopaminergic cell firing.
Gratton
A
A
Douglas Hospital Research Center, McGill University, Verdun, Quebec, Canada.
Hoffer
B J
BJ
Gerhardt
G A
GA
Wise
R A
RA
D000818:Animals; D018492:Dopamine Antagonists; D004357:Drug Synergism; D005444:Flunarizine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009627:Nomifensine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D013239:Stereotyped Behavior / Q000187:drug effects*; D013681:Tegmentum Mesencephali / Q000187:drug effects / Q000502:physiology*
D018492:Dopamine Antagonists; D009627:Nomifensine; D009270:Naloxone; D009020:Morphine; C043424:GBR 13069; D005444:Flunarizine