*2.7. 6-OHDA Toxicity Assay*

After 7–10 days of maintaining dopaminergic culture, the media were removed and different concentrations of 6-OHDA toxin were added (500, 100, 50, 25, 10 and 5 µM) for 24 h to correlate neurotoxin concentration to cell viability; for C+, we just changed the media and, for control negative (C−), DMSO 10% was added. To assess cell viability, after 24 h of incubation with 6-OHDA neurotoxin, the media were removed and the cells were fixed with 3.7% paraformaldehyde (PFA) for 10 min and, then, washed three times in PBS. DAPI staining (1:10,000) in PBS for 15 min was used to determine viable cells. For cell viability quantification, fluorescence microscopy images were obtained by means of an inverted microscope (Nikon TMS, Hampton, NH). Two images per well and three wells were used for each group; in total, six images were taken per group. Dopaminergic cells were scored as positive if they exhibited defined nuclear counterstaining. The data are expressed as the percentage of the C<sup>+</sup> group with no treatment, which was set as 100%.
