(A) PC12 cells were stimulated with glutamate (1, 5, 10 mM) or vehicle control for 24 h and cell viability then was measured with the MTT assay. (B and C) Undifferentiated PC12 cells were treated with PFF (10 μM) for 45 min before glutamate stimulation (5 mM). After 24 h, the neuroprotective effects of PFF were assessed with an inverted phase-contrast microscope (for morphological changes, B; scale bars = 25 μm) and the MTT assay (for cell viability, C). (D) Retinoic acid-mediated differentiated PC12 cells were incubated with PFF (10 μM) for 45 min before glutamate stimulation (5 mM). After 24 h, cell viability was analyzed by MTT assay. Data represent the means and SD of three independent experiments. *p < 0.05, ***p < 0.001 vs. the control group. SC, vehicle control (0.01% DMSO), Glut, glutamate.