1,2-Diacetylbenzene Neurotoxicity: A Model to Study the Role of Schwann Cells in Maintenance of Axonal Integrity in Toxic States

Twenty-five years ago, one of us postulated the existence of a dynamic mechanism for the selective glial sequestration and removal of effete organelles (mitochondria, vesicles, dense bodies) and leprous bacilli from intact axons of myelinated nerve fibers. A thin cytoplasmic sheet derived from the adaxonal Schwann cell or oligodendrocyte invaginates the axon surface, corralls pockets of axoplasm containing the organelles, and removes the cytoplasmic material by phagocytosis (1). This radical proposal was based on inferences drawn from the seemingly logical sequential assembly of transmission electron micrographs depicting static images of mammalian myelinated nerve fibers in normal and pathologic states. Direct evidence to support this proposal came from the use of light/fluorescence, confocal laser, and/or electron microscopy to trace the fate of fast transported radiolabel injected intraspinally, of red-fluorescent latex nanospheres taken up at a sciatic nerve crush site, and of intramuscularly injected horseradish peroxidase endocytosed by intact synaptic terminals (2,3).