Fast axonal diffusion of 3000 molecular weight dextran amines

Abstract

The distances of anterograde and retrograde axonal movement per hour were examined for dextran amines of 3000, 10,000 and 40,000 molecular weights (MW) conjugated to different fluorochromes (Cascade blue, fluorescein, tetramethylrhodamine, Texas red) or to biotin. Lateral line nerves of Xenopus laevis tadpoles were used as an easily accessible test system. Only 10,000 and 3000 MW dextran amines underwent significant anterograde and retrograde movement. Dextrans of 3000 MW progressed about twice as far (2 mm/h at 22 degrees C) than 10,000 MW dextrans. Dextrans conjugated to different fluorochromes or to biotin did not show differences in their distance covered. Tracers traveled over the same distance in amphibians pre-treated with either 1 microM colchicine for 2-6 h or 10 micrograms/ml nocodazole for 5 h prior to the application to depolymerize microtubules needed for active transport. This suggests that diffusion is the major mechanism of movement for dextran amines over short distances. In the developing Xenopus retina, 3000 MW dextrans traveled from the optic disc as far away as the ora serrata within 1 h. In mouse embryos, chicken embryos and larval lampreys dextran amines progress within 1 h from cut peripheral nerves through efferent and afferent tracts. These data show that 3000 MW dextrans can be used in much the same way as 10,000 MW dextrans, but label neuronal profiles in a shorter time in a wide variety of species.