Freeze-fracture Analysis of Myelin Membrane Changes in
Wallerian Degeneration

The intramembranous particles in the myelin membrane generally range between two sizes and shapes: large, globular particles and low height, elongated particles.  In the progression of degenerative myelin changes leading to eventual loss of myelin membrane, the early changes include a clustering of the larger more globular particles, while the more elongated particle components remain dispersed.  Eventually there is a loss of all particles from myelin membrane undergoing intracellular degradation.

Of interest was the observation that for at least a day or more the axon membrane remained unchanged after transection, even though the axonal cytoplasm was greatly altered.  This lack of clustering following transection indicates that the clustering changes noted in the biochemical enrichment experiments are not a general response to injury and more likely reflect the composition of the membrane and the specific conditions of the isolation procedure.  Also, axons may conduct impulses for more than a day after transection, an observation in agreement with our observation that the axon membrane does not seem to be missing integral membrane components at these early time periods.

Because of the differential behavior of subgroups of myelin intramembranous particles, it is important to determine which particles correspond to which biochemical components of the myelin sheath.