Brain, Vol 120, Issue 11 2071-2082, Copyright © 1997 by Oxford University Press
SF Hunter, JA Leavitt and M Rodriguez
We studied patches of CNS myelin in human retina in vivo to determine the
pattern of myelination and the local influence of axons. We analysed the
position, area and thickness of the nerve-fibre layer in 60 patches of
retinal myelin in 47 eyes (in 37 adults and two adolescents). Five patches
in four eyes were studied serially over 6-11 years. Nerve-fibre layer
thickness was obtained from an atlas of primate retina, and volumes of
myelinated tissue were then estimated for each patch. Retinal myelination
occurred in three patterns: thick patches contiguous with the optic disc
(type I); thin, striated patches detached from the disc (type II); or
massive myelination of the posterior pole associated with severe amblyopia
(type III). The papillomacular bundle did not myelinate in types I and II
and was relatively spared in type III patches, suggesting that migratory
oligodendrocyte progenitors are not supported by these axons. The local
nerve-fibre layer determined patch size, and quantal myelination was
evident with modal peaks of patch volume at 0.16 and 0.64 mm3. Myelination
advanced at patch edges when observed over time, consistent with the
hypothesis that new oligodendrocytes are produced in adulthood. We propose
a theoretical model where patches of retinal myelination are the clonal
progeny of a few oligodendrocyte progenitors exhibiting two different
behaviours. First, a highly migratory, nonmyelinating progenitor uses
larger, phylogenetically older axons as the substrate for movement.
Secondly, a more mature progenitor generates myelinating oligodendrocytes
well into adult life, but traverses only short distances. Using this data,
we can estimate the number of oligodendrocytes in these clones and
population doubling- time. This study supports a role for axon-derived
signals in the regulation of human oligodendrocyte progenitor behaviour and
myelination in vivo.
ARTICLES
Direct observation of myelination in vivo in the mature human central nervous system. A model for the behaviour of oligodendrocyte progenitors and their progeny
Department of Neurology, Mayo Clinic, Rochester, USA.
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