Global 5hmC and 5mC content in the hippocampus of young and old mice. DNA was extracted from hippocampal samples of 2- and 22-month-old mice (A, B), and 4- and 24-month-old mice (C, D). DNA was analyzed with 5hmC and 5mC ELISA assays. Results (open bars, young mice; filled bars, old mice) are expressed in units (mean ± SEM; n = 5–6; *P<0.05 compared to the corresponding young group).