GROWTH cones are capable of advancing despite linkage to a stationary axonal cytoskeleton in chick and murine dorsal root ganglion neurites1,2. Several lines of evidence point to the growth cone as the site of cytoskeletal elongation3,4. Fast axonal transport is probably the means by which cytoskeletal elements5 or cofactors are rapidly moved through the axon. We report that direct, but reversible, inhibition of fast axonal transport with laser optical tweezers inhibits growth cone motility if cytoskeletal attachment to the cell body is maintained. Advancement ceases after a distance-dependent lag period which correlates with the rate of fast axonal transport. But severing the axonal cytoskeleton with the laser tweezers allows growth cones to advance considerably further. We suggest that axon elongation requires fast axonal transport but growth cone motility does not.
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