Axonal Flow and Myelin Protein in the Optic Pathway

Abstract

DURING the past two decades the original findings of Weiss and Hiscoe¹ relating to axonal transport have been repeatedly confirmed and extended in several systems. Many macro-molecules and subcellular components are now believed to be formed in the neuronal perikaryon and to pass down the axon. Recent studies indicate that axonal transport of protein occurs at different rates, some material travelling slowly while others move more rapidly^2–4. In the rabbit optic pathway, for example, at least four different waves of proteins reach the lateral geniculate body⁴, one major site of synaptic terminals for optic fibres. The identification of the subcellular components associated with different flows is still under investigation. Certain components of the axolemma and synaptosomes (refs. 5–7 and unpublished results of L. Ericson, H. A. Hansson, J. O. K. and J. S.), neurotransmitter-containing vesicles⁸ and fucose-containing glycoproteins⁹ seem to be transported in the rapid phase. The slow phase of axonal transport is likely to involve most of the soluble proteins in the axon¹⁰, including the subunit of the neuro-tubular protein^11,12. In contrast to the rapid phase of axonal transport a considerable portion of the radioactivity associated with the slow phase does not reach the nerve terminals at the lateral geniculate body, but remains in the nerve⁷. This suggests local utilization of proteins in the axon⁴.