Repeated cocaine modifies the mechanism by which amphetamine releases dopamine.
This study determined whether daily cocaine administration initiates a calcium requirement for the increase in extracellular dopamine produced by psychostimulants. The increase in extracellular dopamine induced by perfusion of amphetamine through a microdialysis probe in the nucleus accumbens shell was enhanced in cocaine- relative to saline-pretreated rats. The augmented portion of the amphetamine-induced increase in nucleus accumbens dopamine was abolished by the coperfusion of L- or N-type calcium channel blockers. Inhibition of calcium/calmodulin-dependent protein kinase II (CaM-KII) also prevented the augmented increase in dopamine by amphetamine, whereas inhibition of vesicular exocytosis by botulinum toxin B was ineffective. When the concentration of extracellular dopamine in the nucleus accumbens was elevated by blocking the plasmallemal dopamine transporter with GBR-12909, the augmented increase in extracellular dopamine in rats sensitized to repeated cocaine was blocked by a CaM-KII inhibitor. Pretreatment with botulinum toxin B prevented the increase in extracellular dopamine by GBR-12909 in both cocaine-pretreated and control rats. Taken together, these results demonstrate that the psychostimulant-induced enhanced increase in extracellular dopamine in the nucleus accumbens shell of cocaine-pretreated rats arises from the induction of calcium- and CaM-KII-dependent mechanisms.
Pierce
R C
RC
Alcohol and Drug Abuse Program, Washington State University, Pullman, Washington 99164-6520, USA.
Kalivas
P W
PW
D000661:Amphetamine / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D003042:Cocaine / Q000008:administration & dosage / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D008297:Male; D017551:Microdialysis; D051381:Rats; D017207:Rats, Sprague-Dawley
D000661:Amphetamine; D003042:Cocaine; D004298:Dopamine