Intracerebroventricular injection of α-synuclein preformed fibrils do not induce motor and olfactory impairment in C57BL/6 mice

Introduction: Alpha-synuclein (alpha Syn) is believed to play a central role in the pathogenesis of Parkinson's disease (PD). Cerebrospinal fluid (CSF) total alpha Syn were significantly lower in PD patients, whereas the aggregates were higher, and this phenomenon was further exacerbated with longer disease duration. However, whether CSF alpha Syn can be the cause and/or a consequence in PD is not fully elucidated. Method: We administered 2 ng or 200 ng alpha Syn preformed fibrils (PFFs) by intracerebroventricular injection for consecutive 7 days in C57BL/6 mice. The olfactory function was assessed by the olfactory discrimination test and buried food-seeking test. The locomotor function was assessed by the rotarod test, pole test, open field test and CatWalk gait analysis. Phosphorylated alpha Syn at serine 129 was detected by the immunohistochemistry staining. Iron levels was determined by Perl's-diaminobenzidine iron staining and synchrotron-based X-ray fluorescence. Results: The mice did not exhibit any diffuse synucleinopathy in the brain for up to 30 weeks, although alpha Syn PFFs induced aggregation in SH-SY5Y cells and in the substantia nigra and striatum of mice with stereotactic injection. No impairment of motor behaviors or olfactory functions were observed, although there was a temporary motor enhancement at 1 week. We then demonstrated iron levels were comparable in certain brain regions, suggesting there was no iron deposition/redistribution occurred. Conclusion: The intraventricular injection of alpha Syn PFFs does not induce synucleinopathy or behavioral symptoms. These findings have implications that CSF alpha Syn aggregates may not necessarily contribute to the onset or progression in PD.