We have generated a transgenic mouse line overexpressing mutated human A30P α-synuclein under the control of the prion-related protein promoter. Immunohistology revealed mutated human A30P α-synuclein protein in numerous brain areas, but no gross morphological changes, Lewy bodies, or loss of dopaminergic cell bodies. The transgenic mice displayed decreased locomotion, impaired motor coordination, and balance. In vivo voltammetry showed that A30P mice responded to longer stimulation of the ascending dopaminergic pathways with less dopamine release in striatum and had a slower rate of dopamine decline after repeated stimulations or after α-methyl-p-tyrosine-HCl treatment. However, dopamine re-uptake or transporter levels were similar in transgenic and control mice. Our data provide evidence that overexpression of mutated human A30P α-synuclein in mice leads to a reduced size of the dopamine storage pool. This is in agreement with the previously postulated involvement of α-synuclein in the turnover of transmitter vesicles and may explain the observed motor deficits in A30P mice. © 2005 Elsevier Inc. All rights reserved.