Protein transport in intact and severed (anucleate) crayfish giant axons

Using video-enhanced microscopy and a pulse-radiolabeling paradigm, we show that proteins synthesized in the medial giant axon cell body of the crayfish (Procambarus clarkii) are delivered to the axon via fast (approximately 62 mm/day) and slow (approximately 0.8 mm/day) transport components. These data confirm that the medial giant axon cell body provides protein to the axon in a manner similar to that reported for mammalian axons. Unlike mammalian axons, the distal (anucleate) portion of a medial giant axon remains intact and functional for > 7 months after severance. This axonal viability persists long after fast transport has ceased and after the slow wave front of radiolabeled protein has reached the terminals. These data are consistent with the hypothesis that another source (i.e., local glial cells) provides a significant amount of protein to supplement that delivered to the medial giant axon by its cell body.