GDNF and Cognitive impairment: The key findings of this study are that (1) compared to young mice, old mice have (a) cognitive impairment, (b) brain abnormalities with GSH deficiency, elevated OxS, impaired mitochondrial function, abnormal mitophagy and autophagy, diminished glucose transporters/uptake, elevated inflammation and higher genomic damage; (c) low brain neurotrophic factors (BDNF, GDNF and NGF); and (2) supplementing old mice with GlyNAC improved/reversed these brain defects, and improved cognition.