Exercise training affects markers of mitochondrial dynamics in the brain. Mitochondrial dynamics was assessed by Western blotting for markers of mitochondrial fission and fusion, DRP1 and MFN2, respectively. Protein levels of DRP1 were significantly elevated in the cortex of old, exercised mice (A), however levels were unchanged in young mice in response to exercise training (B). *P < 0.05 vs. OC, YC and YT. Protein levels of MFN2 were unchanged after exercise in either striatum or cortex of old (C) or young (D) mice. Data are presented as means ± SD. YC, N=8; YT, N=8; OC, N=7; OT, N=7.