INTRODUCTION: According to Braak's hypothesis, Parkinson's disease (PD) pathology may originate in the lower brainstem and spread rostrally before affecting the substantia nigra, which could explain the presence of non-motor prodromal symptoms such as sleep disturbances, depression, and anxiety preceding classical motor deficits. Experimental models reflecting this early-stage progression are crucial for understanding the mechanisms underlying prodromal PD.

AIM(S): The aim of this study was to develop and characterize an experimental mouse model of early-stage Parkinson’s disease by bilateral stereotaxic administration of preformed fibrils of α-synuclein into the brainstem.

METHOD(S): In this study, we modeled early PD-like pathology in C57BL/6J mice by bilateral stereotaxic injections of α-synuclein preformed fibrils into the dorsal motor nucleus of the vagus nerve (DMV). Animals were sacrificed at 1, 3, and 6 months post-injection to assess the temporal progression of α-synuclein pathology. Brain tissues were collected, sectioned, and processed for fluorescent immunohistochemistry using markers for α-synuclein aggregates (phosphoS129), Tph-positive serotonergic neurons, and TH-positive dopaminergic neurons.

RESULTS: Fluorescence staining revealed that, one month after injection, α-synuclein aggregates were confined to the dorsal motor nucleus of the vagus nerve. At three months, pathological inclusions began to spread rostrally toward the raphe nuclei. By six months post-injection, α-synuclein aggregates were clearly detected within the raphe nuclei, indicating progressive propagation of synucleinopathy along anatomically connected pathways.

CONCLUSIONS: These findings demonstrate that brainstem administration of preformedd fibrils of α-synuclein recapitulates key features of PD pathology progression consistent with Braak's staging hypothesis. This model may provide a valuable platform for investigating early, non-motor mechanisms of Parkinson's disease and for exploring therapeutic strategies targeting prodromal stages.

FINANCIAL SUPPORT: This research work was supported by the National Science Centre (Poland) under grant number: 2024/53/N/NZ4/01662 (Preludium 23).