DRD1 and Parkinson disease: The RT-qPCR results showed that the relative mRNA expression of Drd1 was significantly decreased in the mice from the PD-EE group, compared to that in the mice from the PD-SC group, but the expression of Slc6a3 was significantly increased in the mice from the PD-EE group, compared to that in the mice from the PD-SC group (Figure 3C).