Remodeling Myelin

New oligodendrocytes in the adult mouse brain appear to remodel existing myelin sheaths, which may fine-tune the speed of nerve impulses.

Aug 1, 2013
Dan Cossins


LAYING INSULATION: An oligodendrocyte myelinates neuronal axons in the central nervous system by extending a spiral of cytoplasmic membrane that comprises the myelin sheath.© FRANCIS LEROY, BIOCOSMOS/SCIENCE SOURCE

The paper
K.M. Young et al., “Oligodendrocyte dynamics in the healthy adult CNS: evidence for myelin remodeling,” Neuron, 77:873-85, 2013.

The problem
Oligodendrocytes (OLs) produce the myelin sheaths that electrically insulate axons. Although most OLs are generated in the early postnatal period, oligodendrocyte progenitors (OPs) generate mature OLs well into adulthood. The function of these adult-generated OLs is unclear, however—are they myelinating the remaining naked axons, or remodeling existing myelin?

The finding
William Richardson of University College London and colleagues labelled OPs and their OL progeny in the adult mouse brain. If new OLs myelinate naked axons, one would expect to see few new OLs in the mature optic nerve, where 99 percent of axons are fully myelinated. But the researchers observed lots of new OLs there—far more than would be required to myelinate the remaining unmyelinated axons.

The conclusion
“The observations clearly indicate that there is active remodeling of myelin sheaths in the mature brain by newly generated oligodendrocytes,” says Akiko Nishiyama, a neurobiologist at the University of Connecticut who was not involved in the study. The researchers also noticed that stretches of myelin produced by new OLs are shorter and more numerous than those formed by earlier-generated OLs.

The implication
Richardson speculates that this may be a way to fine-tune the speed of action potentials as the animal grows. “It may even have some significance for neural plasticity and learning,” he adds. But the researchers also found that many new OLs also produced one long internode, so it’s possible the short internodes are by-products of the long ones used to myelinate the few naked axons left in the optic nerve.