(A) MLA (20 µM, 30 min), a specific antagonist of α 7 nAChR, increased the level of cell death when administered prior to nicotine (2 mM, 30 min) and MPP+ (500 µM, 24 hrs) treatments in SH-SY5Y cells, as compared to those treated with nicotine and MPP+ alone. ***p < 0.001 as compared to those of control group, #p < 0.05 as compared to MPP+ group, n = 4, one-way ANOVA followed by Tukey’s test. (B) MLA (20 µM, 30 min), a specific antagonist of α7 nAChR, increased the level of SH-SY5Y cell death when administered prior to choline (1 mM, 30 min) and MPP+ (500 µM, 24 hrs) treatments, as compared to those treated with choline and MPP+ alone. ***p < 0.001 compared to the control group, #p < 0.05 as compared to the MPP + group, n = 4, one-way ANOVA followed by Tukey’s test. All data are shown as mean ± SEM. The level of cell death was detected using PI and Hoechst33342 double staining, and was defined as the ratio of fluorescent intensity of PI: Hoechst33342.