Axon-glia transfer of a protein and a carbohydrate

We have investigated the transfer of a fluorescent protein, the fluorescein isothiocyanate derivative of bovine serum albumin (FITC-BSA), and a fluorescent carbohydrate, FITC-dextran, from the crayfish medial giant axon (MGA) to the periaxonal glial cells. The dialyzed tracer was injected into one of the two MGAs, and, after a transfer period of 15-60 min, the tissue was fixed for histological examination of fluorescence distribution. With each tracer, the periaxonal sheath of the injected MGA was specifically labeled. Similar results were obtained with several different fixatives. During the transfer period, there was no appreciable change in the resting potential or conducted action potential of the MGA or in the resting potentials of the adaxonal glial cells. Polyacrylamide gel electrophoresis indicated that the axoplasmic and sheath fluorescence was produced by the intact tracers. These results suggest that "foreign" macromolecules can be exchanged from crayfish axons to glia under physiological conditions. Such transfers may indicate a substantial intercellular traffic of molecules or a means whereby neurons can eliminate waste materials.