This analysis confirmed a marked reduction in DRD2 expression within TH‐positive dopaminergic neurons of the substantia nigra in hSNCA Tg mice only, thereby reinforcing the association between α‐synuclein overexpression, DRD2 downregulation, and PD‐related dopaminergic dysfunction (Figure 5D,E). This evidence concerns the gene TH and Parkinson disease.