Slow Axonal Transport in Nerve from Mice with a Genetic Myelin Deficiency (Trembler)

Abstract

In a myelinated nerve, there is a relation between axonal diameter and the size of its myelin sheath: the larger the diameter of the axon, the thicker the myelin sheath. When the axonal diameter increases above 1 micron during development or regeneration, myelin formation in surrounding Schwann cells is triggered. However, recent studies suggest that the relation between axon and Schwann cell is more complex. In experiments involving sciatic nerve grafts between the normal and the myelin deficient mutant Trembler mice, Schwann cells were shown to locally influence the morphology and the diameter of axons (A.Aguayo 1977). Axonal diameter is dependent on its cytoskeleton and the cytoskeletal proteins are moving along the axon with the slow components of axonal transport. When slow axonal transport of the cytoskeletal protein decreases, as during regeneration for instance, one observes that the reduction in transport correlates with the decrease in axonal diameter. This has been quantified by Hoffman et al. for the neurofilament protein (Hoffman 1986).