Fig. 3.

MIMIR of middle-aged (12- to 13-mo-old) and old (23- to 25-mo-old) mice reveals age-related changes in axonal transport of mitochondria in vivo. (A–D) MIMIR of middle-aged (A and Movie S9) and old (C and Movie S10) mice. (Scale bar in C, 10 μm.) The kymographs detected active axonal transport of mitochondria in middle-aged (B) and old (D) mice. (E–G) The number of mitochondria transported in axons (E) and anterograde (F) and retrograde (G) transport did not change with age. (H–J) The duration (H, *P < 0.0001, **P = 0.04) and distance (I, *P < 0.0001, **P = 0.0005) of transport and the duty cycle (J, *P < 0.0001) decreased with aging. (K) The averages of the transport velocity in the four age groups converged toward ∼0.2 μm/s; *P = 0.02. (L) The mitochondria-free regions in axons increased with aging; *P = 0.0002, **P = 0.02. (M) The length of mitochondria transported in axons decreased with aging; *P < 0.0001, **P = 0.0006. Dunn’s two-tailed test was used in E–M. (N) Similar proportions of the four transport patterns through the four age groups suggest totally organized transport patterns are preserved in old mice. The sample size (n) is given in SI Appendix, Table S1.