Retrograde transport of radiolabeled cytoskeletal proteins in transected nerves.

Slow axonal transport is the mechanism by which cytoskeletal proteins are distributed within the axon. This function has traditionally been considered an exclusively unidirectional, anterograde process. Previous observations of cytoskeletal redistribution in surviving, transected axons of the C57BL/Ola mouse led us to hypothesize a retrograde component of cytoskeletal transport. To test this hypothesis against previous methods of measuring slow transport of cytoskeleton, we radioactively pulse-labeled proteins in sensory neurons of C57BL/Ola mice and followed their redistribution by gel fluorography in ligated and unligated sciatic nerves. Slow axonal transport of cytoskeletal proteins proceeded with the same characteristics in C57BL/Ola as in standard C57BL/6 mice. In comparison to the transport profiles from unligated control nerves, in ligated nerves there was redistribution of radiolabeled neurofilament and tubulin proteins back toward the cell body during the 14 d experimental period. These observations demonstrate that pulse-labeled cytoskeletal proteins move bidirectionally in this experimental system, and may provide insight into the normal mechanisms of cytoskeletal maintenance.