Abstract
Endogenous striatal dopamine (DA) overflow has been associated with neuropathological conditions resulting from ischemia, psychostimulants, and metabolic inhibition. Malonate, a reversible inhibitor of succinate dehydrogenase, models the effects of energy impairment in neurodegenerative disorders. We have previously reported that the striatal DA efflux and damage to DA nerve terminals resulting from intrastriatal malonate infusions is prevented by prior DA depletion, suggesting that DA plays a role in the neuronal damage. We presently report that the malonate-induced DA efflux is partially mediated by reverse transport of DA from the cytosol to the extracellular space via the DA transporter (DAT). Pharmacological blockade of the DAT with a series of structurally different inhibitors [cocaine, mazindol, 1-(2-(bis(4-fluophenyl methoxy) ethyl)-4-(3-(4-fluorophenyl)-propyl)piperazine) dimethane sulfonate (GBR 13098) and methyl(–)-3β-(p-fluorophenyl)-1αH,5αH-tropane-2β-carboxylate1,5-naphthalene (Win 35,428)] attenuated malonate-induced DA overflow in vivo and protected mice against subsequent damage to DA nerve terminals. Consistent with these findings, the DAT inhibitors prevented malonate-induced damage to DA neurons in mesencephalic cultures and also protected against the loss of GABA neurons in this system. The DAT inhibitors did not modify malonate-induced formation of reactive oxygen species or lactate production, indicating that the DAT inhibitors neither exert antioxidant effects nor interfere with the actions of malonate. Taken together, these findings provide direct evidence that mitochondrial impairment and metabolic stress cause striatal DA efflux via the DAT and suggest that disruptions in DA homeostasis resulting from energy impairment may contribute to the pathogenesis of neurodegenerative diseases.
Footnotes
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This work was supported by National Institutes of Health Grants MH12390 (to L.Y.M.) and AG08479 and NS41545 (to P.K.S.)
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.106.110791.
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ABBREVIATIONS: DA, dopamine; ROS, reactive oxygen species; DAT, plasma membrane dopamine transporter; WIN 35,428, methyl(–)-3β-(p-fluorophenyl)-1αH,5αH-tropane-2β-carboxylate1,5-naphthalene; CFDA, carboxyfluorescein diacetate; GBR 13098, 1-(2-(bis(4-fluophenyl methoxy) ethyl)-4-(3-(4-fluorophenyl)-propyl)piperazine) dimethane sulfonate; DCF, 2′,7′-dichlorofluorescein diacetate; DOPAC, dihydroxyphenylacetic acid; HPLC, high-performance liquid chromatography; TH, tyrosine hydroxylase; HBS, HEPES-buffered saline; DMEM, Dulbecco's modified Eagle's medium; CM, conditioned medium; KRB, bicarbonate-buffered Krebs-Ringer; CF, carboxyfluorescein.
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↵1 Current affiliation: MIT Picower Institute, Cambridge, Massachusetts.
- Received July 14, 2006.
- Accepted November 6, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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