Movement of mitochondria in the axons and dendrites of cultured hippocampal neurons

Mitochondria generate ATP and are involved in the regulation of cytoplasmic calcium levels. It is thought that local demand for mitochondria differs b etween axons and dendrites. Moreover, it has been suggested that the distri bution of both energy need and calcium flux in dendrites changes with patte rns of synaptic activation, whereas the distribution of these demands in ax ons is stable. The present study sought to determine whether there are diff erences in mitochondrial movements between axons and dendrites that may rel ate to differences in local mitochondrial demand. We labeled the mitochondr ia in cultured hippocampal neurons with a fluorescent dye and used time-lap se microscopy to examine their movements. In both axons and dendrites, appr oximately one-third of the mitochondria were in motion at any one time. In both domains, approximately 70% of the mitochondria moved in the anterograd e direction, whereas the remainder moved in the retrograde direction. The v elocity of the movements in each direction in each domain ranged from 0.1 m um/sec to approximately 2 mum/sec, and the means and distributions of the v elocities were similar. Only one difference in the behavior of mitochondria between axons and dendrites emerged from this analysis. Mitochondria in ax ons were more likely to move with a consistently rapid velocity than were t hose in dendrites. As a result, mitochondria in axons tended to travel fart her than mitochondria in dendrites. These results suggest that the transpor t of mitochondria in axons and dendrites is similar despite any differences in mitochondrial demand between the two domains. (C) 2000 Wiley-Liss, Inc.