Fundamentals of Neuronal Transport of Gangliosides. Functional Implications

Abstract

When ganglioside transport studies were first undertaken approximately 15 years ago, relatively little was known about the localization of gangliosides within the neuron, their site of synthesis or the means of conveyance from the latter to the former. Elucidation of the phenomenon of axonal transport has helped to provide at least a partial answer to these questions, and is now providing additional insight into possible functional roles for these substances. The problem of logistics is particularly acute for the neuron with its enormous network of processes, these often being several thousand times greater in length than the diameter of the cell body. Hence it was logical to suppose in the beginning that the neuron solved this problem by in situ synthesis, e.g. in the nerve-ending or processes themselves; indeed, some studies of that early period reported evidence for glycosyltransferase activity in isolated synaptosomes. However, as methodology improved it developed that much if not all such activity was the result of contamination, and it has since become generally accepted that the cell body is the major — perhaps only — locus of synthesis. We shall attempt to briefly review the studies which led to this conclusion and indicate some of the still unresolved questions. We shall also refer to a more recently discovered mode of ganglioside transport, catalyzed by soluble transfer proteins in brain, and discuss certain functional implications of all these phenomena.