The effects of the GPR4 antagonist NE52-QQ57 on the expression of pro-apoptotic proteins, cleaved PARP and cleaved caspase 3, and caspase 3 activity in MPTP-treated mice. MPTP was administered (30 mg/kg/day) for 5 days. Mice were sacrificed, and the substantia nigra and striatum tissue was collected 3 days after the final MPTP administration. (a) Cleaved PARP-1 and cleaved caspase 3 protein expression and caspase 3 activity assay in the mouse SNpc (n = 3) and densitometric analysis. (b) Cleaved PARP-1 and cleaved caspase 3 protein expression and caspase 3 activity assay in the mouse striatum (n = 3) and densitometric analysis. β-Actin was utilized as an internal control. Data are presented as the mean ± SEM. One-way ANOVA, followed by Tukey’s multiple comparison test, was used to compare differences between groups. # p < 0.05 when the MPTP-treated group was compared with the vehicle-only group; * p < 0.05 when the other treated groups were compared with the MPTP-treated group.