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Alzheimer's disease (AD) is often accompanied by extrapyramidal signs attributed to nigrostriatal dysfunction. The association between amyloid deposition and nigrostriatal degeneration is essentially unknown. We showed previously that the striatum and the substantia nigra of transgenic mice harboring familial AD (FAD)-linked APPswe/PS1ΔE9 mutants exhibit morphological alterations accompanied by amyloid-β (Aβ) deposition (Perez et al., 2004). In the present study, we further investigated the interaction between Aβ deposition and dopaminergic nigrostriatal dysfunction, by correlating morphological and biochemical changes in the nigrostriatal pathway with amyloid deposition pathology in the brains of 3- to 17-month-old APPswe/PS1ΔE9 transgenic mice and age-matched wild-type controls. We show that Aβ deposition is pronounced in the striatum of APPswe/PS1ΔE9 mice at 6 months of age, and the extent of deposition increases in an age-dependent manner. Tyrosine hydroxylase (TH)-positive dystrophic neurites with rosette or grape-like cluster disposition are observed adjacent to Aβ plaques and display multilaminar, multivesicular, and dense-core bodies as well as mitochondria. In addition, an age-dependent increase of TH protein levels are shown in nigral cells in these mutant mice. Using HPLC analysis, we found a reduction in the dopamine metabolite DOPAC in the striatum of these mice. These findings show a close association between amyloid deposition and nigrostriatal pathology and suggest that altered FAD-linked amyloid metabolism impairs, at least in part, the function of dopaminergic neurons. [ABSTRACT FROM AUTHOR]