Dopamine uptake through the norepinephrine transporter in brain regions with low levels of the dopamine transporter: evidence from knock-out mouse lines.
Selective blockers of the norepinephrine transporter (NET) inhibit dopamine uptake in the prefrontal cortex. This suggests that dopamine in this region is normally cleared by the somewhat promiscuous NET. We have tested this hypothesis by comparing the effects of inhibitors selective for the three monoamine transporters with those of a nonspecific inhibitor, cocaine, on uptake of 3H-dopamine into synaptosomes from frontal cortex, caudate nucleus, and nucleus accumbens from wild-type, NET, and dopamine transporter (DAT) knock-out mice. Dopamine uptake was inhibited by cocaine and nisoxetine, but not by GBR12909, in frontal cortex synaptosomes from wild-type or DAT knock-out mice. At transporter-specific concentrations, nisoxetine and GBR12909 failed to block dopamine uptake into frontal cortex synaptosomes from NET knock-out mice. The efficacy of cocaine at the highest dose (1 mm) was normal in DAT knock-out mice but reduced by 70% in NET knock-out mice. Nisoxetine inhibited dopamine uptake by 20% in caudate and nucleus accumbens synaptosomes from wild-type and DAT knock-out mice but had no effect in those from NET knock-out mice. Cocaine failed to block dopamine uptake into caudate or nucleus accumbens synaptosomes from DAT knock-out mice. Cocaine and GBR12909 each inhibited dopamine uptake into caudate synaptosomes from NET knock-out mice, but cocaine effectiveness was reduced in the case of nucleus accumbens synaptosomes. Thus, whereas dopamine uptake in caudate and nucleus accumbens depends primarily on the DAT, dopamine uptake in frontal cortex depends primarily on the NET. These data underscore the fact that which transporter clears dopamine from a given region depends on both the affinities and the local densities of the transporters.
Morón
Jose A
JA
Behavioral Neuroscience Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, USA.
Brockington
Alicia
A
Wise
Roy A
RA
Rocha
Beatriz A
BA
Hope
Bruce T
BT
D000818:Animals; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry; D002421:Caudate Nucleus / Q000737:chemistry / Q000378:metabolism; D003042:Cocaine / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism* / Q000493:pharmacokinetics; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005473:Fluoxetine / Q000031:analogs & derivatives* / Q000494:pharmacology; D005625:Frontal Lobe / Q000737:chemistry / Q000378:metabolism; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins; D009638:Norepinephrine / Q000037:antagonists & inhibitors; D050484:Norepinephrine Plasma Membrane Transport Proteins; D009714:Nucleus Accumbens / Q000737:chemistry / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology; D027981:Symporters / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D013574:Synaptosomes / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism
D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D050484:Norepinephrine Plasma Membrane Transport Proteins; D010879:Piperazines; C493228:Slc6a2 protein, mouse; C493215:Slc6a3 protein, mouse; D027981:Symporters; D005473:Fluoxetine; C011386:nisoxetine; C043425:vanoxerine; D003042:Cocaine; D004298:Dopamine; D009638:Norepinephrine