Brainstem and spinal cord of aged symptomatic M83 mice were dissected from brains previously stored at −80°C. Tissue was sonicated in sterile PBS (100 mg per 1 ml of buffer) with a handheld probe (QSonica). Homogenates were cleared by centrifugation for 5 min (3,000 g, 4°C) and the resultant supernatant (lysate) was recovered and stored at −80°C until injection. Purification of recombinant α-Syn proteins and in vitro fibril assembly was performed as previously described (Murray et al., 2003 (link); Luk et al., 2009 (link)) using human α-Syn1-120Myc or WT full-length human α-Syn (5 mg/ml). PFFs were collected after 5 d of incubation at 37°C. PFF preparations were diluted into sterile PBS and sonicated briefly before intracerebral injection.