Parkinson's disease (PD) compromises motor control due to the loss of dopaminergic neurons in the substantia nigra pars compacta. At the histopathological level, PD is characterized by the accumulation of Lewy bodies, large protein inclusions containing aggregated alpha Synuclein (alpha Syn). The progression of PD involves the spreading of alpha Syn misfolding through the brain mediated by a prion-like mechanism, where the protein is transferred between cells. Here we report that alpha Syn internalization is a dynamic process, where the protein transits through different sub-cellular compartments. Importantly, cells incorporating aSyn develop larger protein-like inclusions when compared to alpha Syn producing cells. We developed a new tool to monitor cell-to-cell transfer of alpha Syn in vivo using an adeno-associated viral (AAV) vector expressing alpha Syn fused to a red fluorescent protein in addition to soluble EGFP to label donor cells. Intranigral delivery of this reporter AAV construct allowed the visualization of alpha Syn incorporation into surrounding neurons. This work provides a new tool to study aSyn cell-to-cell transfer in vivo and may open new opportunities to study PD pathogenesis. (C) 2018 Elsevier Inc. All rights reserved.