Like in other studies24, we found that the abundance of dopaminergic neurons (as indicated by tyrosine hydroxylase (TH) immunostaining intensities) in the substantia nigra was significantly lower in the vehicle-treated MPTP-induced PD model group than in the normal control group, and that this change was abrogated in the plasminogen-treated group (Fig. 5A–D). This evidence concerns the gene TH and Parkinson disease.