Bradykinesia and postural instability in a model of prodromal synucleinopathy with α-synuclein aggregation initiated in the gigantocellular nuclei

α-Synuclein (aSyn) accumulation within the extra-nigral neuronal populations in the brainstem, including the gigantocellular nuclei (GRN/Gi) of reticular formation, is a recognized feature during the prodromal phase of Parkinson disease (PD). Accordingly, there is a burgeoning interest in animal model development for understanding the pathological significance of extra-nigral synucleinopathy, in relation to motor and/or non-motor symptomatology in PD. Here, we report an experimental paradigm for the induction of aSyn aggregation in brainstem, with stereotaxic delivery of pre-formed fibrillar (PFF) aSyn in the pontine GRN of transgenic mice expressing the mutant human Ala53Thr aSyn (M83 line). Our data show that PFF aSyn-induced aggregate pathology in GRN and distinct nuclei of subcortical motor system leads to progressive decline in home cage activity, which was accompanied by postural instability and impaired motor coordination. The progressive accumulation of aSyn pathology in brainstem and motor neurons in lumbar spinal cord heralded the onset of a moribund stage, which culminated in impaired survival. Collectively, our observations suggest an experimental framework for studying the pathological significance of aSyn aggregation in GRN in relation to features of movement disability in PD. With further refinements, we anticipate that this model holds promise as a test-bed for translational research in PD and related disorders.