Silencing of SNCA is resilient and target-specific. SNCA and SNCB expression was assessed by in situ hybridization following extended timecourse of in vivo SNCA siRNA treatment. Qualitative densitometric analysis was performed on mice treated with SNCA siRNA on the right side of the brain and a ratio showing either SNCA or SNCB expression in the treated (R) and untreated (L) brain was calculated and plotted for each animal within a group. The knockdown of SNCA expression (black circle) persists in the (A) CA1 and the (B) cortex two weeks after cannula removal with SNCA approaching normal levels by three weeks post-infusion. The closed triangle indicates SNCA levels in a mouse in which the cannula was loose at the end of the study. Non-specific silencing of SNCB (open circle) was not observed at any timepoint.