To further illuminate the protective effects of estrogens and other polycyclic phenols on mitochondrial integrity, we examined a number of markers of mitochondrial activity in SK-N-SH neuroblastoma cells exposed to 3-nitroproprionic acid (3-NPA). The latter inhibits oxidative phosphorylation by blocking electron entry into electron transport at the level of succinate dehydrogenase (respiratory Complex II), and so serves to model not only acute impaired energy production seen during cerebral ischemia [38,70,71], but also more modest energy impairment associated with chronic neurodegenerative disease [72].We reported that 17β-E2 prevents depletion of ATP, preserves ΔΨm, and inhibits production of reactive oxygen species [1] caused by 3-NPA [73]. Further, we made similar observations of the mitochondrial effects of estrogens when H2O2 was used to impair mitochondrial function [74].