Dysregulation of Intracellular Dopamine Stores Revealed in the R6/2 Mouse Striatum

Abstract

Huntington’s disease is a fatal, neurodegenerative movement disorder characterized by preferential and extensive striatal degeneration. Here, we used fast-scan cyclic voltammetry to study the mobilization and efflux of reserve pool dopamine in striatal brain slices from Huntington’s disease model R6/2 mice. When applying stimulus trains of 120 pulses, evoked dopamine release in wild-type slices was greater than that in R6/2 slices at the higher frequencies (50 and 60 Hz). To quantify cytosolic and reserve pool dopamine levels, amphetamine-induced dopamine efflux was measured after pre-treatment with either tetrabenazine or alpha-methyl-ptyrosine. Slices from 12-week old R6/2 mice released less dopamine than slices from wild-type mice, while no difference was noted in slices from 6-week old mice. The vesicular release of reserve pool dopamine, mobilized by treatment with cocaine, was shorter lived in R6/2 slices compared to wild-type slices even though peak dopamine release was the same. Moreover, the number of dopamine reserve pool vesicles in R6/2 mice was less than half of that in wild-type. Therefore, our data suggest that the same number of dopamine molecules are present in each reserve pool vesicle in WT and R6/2 mice and that these vesicles are readily mobilized in both genotypes; however, R6/2 mice have fewer dopamine reserve pool vesicles available for mobilization.