Role of microtubules and actin filaments in the movement of mitochondria in the axons and dendrites of cultured hippocampal neurons

The mitochondria in the axons and dendrites of neurons are highly motile, b ut the mechanism of these movements is not well understood. It has been tho ught that the transport of membrane-bounded organelles in axons, and perhap s also in dendrites, depends on molecular motors of the kinesin and dynein families. However, recent evidence has suggested that some organelle transp ort, including that of mitochondria, may proceed along actin filaments as w ell. The present study sought to determine the extent to which mitochondria l movements in neurons depend on microtubule-based and actin-based transpor t systems. The mitochondria in cultured hippocampal neurons were labeled wi th a fluorescent dye and the cells were treated with either nocodazole, a d rug that disrupts the microtubule network or cytochalasin D or latrunculin B, drugs which disrupt the actin network. The movement of the mitochondria in the axons and dendrites of neurons after each of these drug treatments w as then examined with time-lapse microscopy. Treatment with nocodazole, whi ch depolymerizes microtubules, stopped most mitochondrial movements in both axons and dendrites. Treatment with cytochalarsin D, which aggregates acti n filaments, also inhibited most movements of mitochondria, but latrunculin B, which depolymerizes actin filaments, had virtually no effect. Together, these data suggest that most of the mitochondrial movements in both axons and dendrites are microtubule-based, but in each domain there may also be s ome movement along actin filaments. (C) 2000 Wiley-Liss, Inc.