Injection of AAV9-SLR and AAV9-NSS resulted in a larger number of tdTomato+/tyrosine-hydroxylase-positive (TH+) neurons in SNc than WT-AAV9 (AAV9-SLR: p=0.0001; AAV9-NSS: p=0.0001; Figure 1C), whereas injection of WT-AAV2 and AAV-RGD resulted in no retrograde infection to SNc. Here, TH is linked to infection.