title: Subcellular localization and molecular topology of the dopamine transporter in the striatum and substantia nigra.
abstract: Plasma membrane transporters remove neurotransmitters from the extracellular space and have been postulated to terminate synaptic activity. Their specific roles in synaptic and nonsynaptic neurotransmission at a cellular level, however, remain unclear. We have determined the subcellular location of the dopamine transporter (DAT) by immunoperoxidase and immunogold electron microscopy, using monoclonal antibodies to both the N-terminus and the second extracellular loop. The two DAT epitopes were found on opposite faces of cellular and intracellular membranes, providing confirmation of the predicted molecular topology of DAT. In the striatum, DAT was localized in the plasma membrane of axons and terminals. Double immunocytochemistry demonstrated DAT colocalization with two other markers of nigrostriatal terminals, tyrosine hydroxylase and D2 dopamine receptors. The latter was thus demonstrated to be an autoreceptor. Labeled striatal terminals formed symmetrical synapses with spines, dendrites, and perikarya. DAT was not identified within any synaptic active zones, however, even using serial section analysis. These results suggest that striatal dopamine reuptake may occur outside of synaptic specializations once dopamine diffuses from the synaptic cleft. In the substantia nigra, DAT appears to be specifically transported into dendrites, where it can be found in smooth endoplasmic reticulum, plasma membrane, and pre- and postsynaptic active zones. These localizations suggest that DAT modulates the intracellular and extracellular dopamine levels of nigral dendrites. Within the perikarya of pars compacta neurons, DAT was localized primarily to rough and smooth endoplasmic reticulum, Golgi complex, and multivesicular bodies, identifying probable sites of synthesis, modification, transport, and degradation.
authors.affiliation: Department of Neurology, Emory University School of Medicine, Atlanta, Georgia 30322, USA. SH@neuro.emory.edu
authors.forename: S M
authors.initials: SM
authors.lastname: Hersch
authors.forename: H
authors.initials: H
authors.lastname: Yi
authors.forename: C J
authors.initials: CJ
authors.lastname: Heilman
authors.forename: R H
authors.initials: RH
authors.lastname: Edwards
authors.forename: A I
authors.initials: AI
authors.lastname: Levey
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D017660:Autoreceptors / Q000378:metabolism / Q000502:physiology; D001369:Axons / Q000378:metabolism; D002352:Carrier Proteins / Q000276:immunology / Q000378:metabolism* / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism* / Q000648:ultrastructure; D003712:Dendrites / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D050483:Dopamine Plasma Membrane Transport Proteins; D000939:Epitopes / Q000276:immunology; D007150:Immunohistochemistry; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D016253:Microscopy, Immunoelectron; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000378:metabolism / Q000502:physiology; D013378:Substantia Nigra / Q000378:metabolism* / Q000648:ultrastructure; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism; D050492:Vesicular Biogenic Amine Transport Proteins
chemical_list: D000911:Antibodies, Monoclonal; D017660:Autoreceptors; D002352:Carrier Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; D000939:Epitopes; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D017448:Receptors, Dopamine D2; C493216:Slc6a3 protein, rat; D050492:Vesicular Biogenic Amine Transport Proteins; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine