Persistence of axonal transport in isolated axons of the mouse

We have examined the hypothesis, for the case of mouse axons, that isolating an axon from its cell body will lead to a rapid failure of fast axonal transport as anterogradely moving organelles vacate the axon in a proximo-distal direction, and retrogradely moving organelles vacate it in the opposite direction. We used CD1 and BALB/c mice and the Wallerian degeneration-resistant mutant C57BL/Ola. Sciatic nerves were cut high in the thigh; at various times up to 8 days later nerves were removed from the animal and individual myelinated axons from the segment distal to the cut were examined by video light microscopy to detect rapid organelle transport. Bidirectional fast organelle transport did decrease in amount with time but not nearly as rapidly as predicted, and anterograde and retrograde organelle velocities remained normal through time. In the C57BL/Ola mouse some structurally preserved axons contained organelles that transported at normal velocities in the anterograde and retrograde directions for as long as 8 days after axotomy. To test one of the possible origins of transported organelles in long-surviving axons we examined organelle transport very close to narrow lesions in axons bathed in a medium compatible with intracellular function. No organelles crossed the lesion but bidirectional organelle transport took place proximal and distal to the lesion; the amounts were compatible with the interpretation that approximately 30% of organelles reversed transport direction on either side of the lesion. We propose that at least some of the organelles that undergo persistent transport in axons isolated from their cell bodies shuttle back and forth between the ends of the isolated segment.