The Journal of Neuroscience, 2002, 22:RC222:1-4
RAPID COMMUNICATION
Lack of Cocaine Effect on Dopamine Clearance in the Core and
Shell of the Nucleus Accumbens of Dopamine Transporter Knock-Out
Mice
Evgeny A.
Budygin,
Carrie E.
John,
Yolanda
Mateo, and
Sara
R.
Jones
Department of Physiology and Pharmacology, Wake Forest University
School of Medicine, Winston-Salem, North Carolina 27157
Cocaine produces its reinforcing effects primarily by inhibiting
the dopamine transporter (DAT) at the level of presynaptic terminals
and increasing extracellular levels of dopamine (DA). Surprisingly, in
mice genetically lacking the DAT, cocaine was still able to elevate DA
in the nucleus accumbens (NAc). This finding is critically important
for explaining the persistence of cocaine reinforcement in DAT
knock-out (DAT-KO) mice. However, the mechanism by which cocaine
elevates DA is unclear. Here, we tested the recently proposed
hypothesis that in the absence of the DAT, the norepinephrine
transporter (NET) could provide an alternative uptake site for DA
clearance. If true, cocaine could elevate DA levels through its
inhibition of the NET. In vitro voltammetry, a technique
well suited for evaluating the effects of drugs on DA uptake, was used
in the present study. We report that both cocaine and desipramine, a
potent NET inhibitor, failed to change DA clearance or evoked release
in the NAc of mutant mice. Additionally, fluoxetine, a serotonin
transporter (SERT) inhibitor, also had no effect on these parameters.
These data rule out the involvement of accumbal NET or SERT in the
cocaine-induced increase in extracellular DA in DAT-KO mice. Moreover,
the present findings suggest that in the DAT-KO mice, cocaine acts
primarily outside the NAc to produce its effects.
Key words:
cocaine; nucleus accumbens; dopamine; DAT knock-out mice; desipramine; voltammetry
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