CASP3 and Parkinson disease: Showing that the GLP-1RA partially alleviated dopaminergic cell death in the MPTP PD model, we further examined the apoptosis of mice substantia nigra cells via TUNEL staining and of cleaved caspase-3 immunohistochemistry staining on mice substantia nigra tissue after four doses of normal saline/MPTP/GLP-1RA/MPTP + GLP-1RA on the 3rd day (Figure 4).