To elucidate the role of alpha-synuclein in the pathogenesis of Parkinson's disease (PD), both human alpha-synuclein transgenic mice and targeted overexpression of human alpha-synuclein in rat substantia nigra (SN) by viral vector-based methods have been studied, however little is known about the pathogenetic changes of dopaminergic neuron loss. Therefore, it is necessary to address whether the pathogenetic changes in the brains of patients with PD are recapitulated in these models.We used the recombinant adeno-associated viral (rAAV) vector system for human alpha-synuclein gene transfer to rat SN and observed approximately 50% loss of dopaminergic neurons in SN at 13 weeks after infection. In the slower progression of neurodegeneration, we identified several important features in common with the pathogenesis of PD, such as phosphorylation of alpha-synuclein at Ser129 and activation of caspase-9. Both findings were also evident in cortical tissues overexpressing alpha-synuclein via rAAV.Our results indicate that overexpression of alpha-synuclein via rAAV apparently recapitulates several important features of brains with PD and dementia with Lewy bodies (DLB), and thus alpha-synucleinopathy described here is likely to be an ideal model for the study of the pathogenesis of PD and DLB. This model is also useful for the gene therapy research.