Axonal myelin increases neural processing speed and efficiency. It is unknown whether patterns of myelin distribution are fixed or whether myelinating oligodendrocytes are continually generated in adulthood and maintain the capacity for structural remodeling. Using high-resolution, intravital label-free and fluorescence optical imaging in mouse cortex, we demonstrate lifelong oligodendrocyte generation occurring in parallel with structural plasticity of individual myelin internodes. Continuous internode formation occurred on both partially myelinated and unmyelinated axons, and the total myelin coverage along individual axons progressed up to two years of age. After peak myelination, gradual oligodendrocyte death and myelin degeneration in aging were associated with pronounced internode loss and myelin debris accumulation within microglia. Thus, cortical myelin remodeling is protracted throughout life, potentially playing critical roles in neuronal network homeostasis. The gradual loss of internodes and myelin degeneration in aging could contribute significantly to brain pathogenesis.
Subscribe to Journal
Get full journal access for 1 year
only $4.92 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Salzer, J. L. & Zalc, B. Myelination. Curr. Biol. 26, R971–R975 (2016).
Nave, K.-A. Myelination and support of axonal integrity by glia. Nature 468, 244–252 (2010).
Waxman, S. G. Axon-glia interactions: building a smart nerve fiber. Curr. Biol. 7, R406–R410 (1997).
Hutchinson, N. A., Koles, Z. J. & Smith, R. S. Conduction velocity in myelinated nerve fibres of Xenopus laevis. J. Physiol. (Lond.) 208, 279–289 (1970).
Hess, A. & Young, J. Z. Correlation of internodal length and fibre diameter in the central nervous system. Nature 164, 490–491 (1949).
Seidl, A. H., Rubel, E. W. & Harris, D. M. Mechanisms for adjusting interaural time differences to achieve binaural coincidence detection. J. Neurosci. 30, 70–80 (2010).
Bennett, M. V. Comparative physiology: electric organs. Annu. Rev. Physiol. 32, 471–528 (1970).
Salami, M., Itami, C., Tsumoto, T. & Kimura, F. Change of conduction velocity by regional myelination yields constant latency irrespective of distance between thalamus and cortex.Proc. Natl. Acad. Sci. USA 100, 6174–6179 (2003).
McGee, A. W., Yang, Y., Fischer, Q. S., Daw, N. W. & Strittmatter, S. M. Experience-driven plasticity of visual cortex limited by myelin and Nogo receptor. Science 309, 2222–2226 (2005).
Tomassy, G. S. et al. Distinct profiles of myelin distribution along single axons of pyramidal neurons in the neocortex. Science 344, 319–324 (2014).
Micheva, K. D. et al. A large fraction of neocortical myelin ensheathes axons of local inhibitory neurons. eLife 5, e15784 (2016).
Hill, R. A. & Nishiyama, A. NG2 cells (polydendrocytes): listeners to the neural network with diverse properties. Glia 62, 1195–1210 (2014).
Zhu, X., Bergles, D. E. & Nishiyama, A. NG2 cells generate both oligodendrocytes and gray matter astrocytes. Development 135, 145–157 (2008).
Dimou, L., Simon, C., Kirchhoff, F., Takebayashi, H. & Götz, M. Progeny of Olig2-expressing progenitors in the gray and white matter of the adult mouse cerebral cortex. J. Neurosci. 28, 10434–10442 (2008).
Kang, S. H., Fukaya, M., Yang, J. K., Rothstein, J. D. & Bergles, D.E. NG2 CNS glial progenitors remain committed to the oligodendrocyte lineage in postnatal life and following neurodegeneration. Neuron 68, 668–681 (2010).
Zhu, X. et al. Age-dependent fate and lineage restriction of single NG2 cells. Development 138, 745–753 (2011).
Young, K. M. et al. Oligodendrocyte dynamics in the healthy adult CNS: evidence for myelin remodeling. Neuron 77, 873–885 (2013).
Hill, R. A., Patel, K. D., Goncalves, C. M., Grutzendler, J. & Nishiyama, A. Modulation of oligodendrocyte generation during a critical temporal window after NG2 cell division. Nat. Neurosci. 17, 1518–1527 (2014).
Gibson, E. M. et al. Neuronal activity promotes oligodendrogenesis and adaptive myelination in the mammalian brain. Science 344, 1252304 (2014).
Liu, J. et al. Impaired adult myelination in the prefrontal cortex of socially isolated mice. Nat. Neurosci. 15, 1621–1623 (2012).
Simon, C., Götz, M. & Dimou, L. Progenitors in the adult cerebral cortex: cell cycle properties and regulation by physiological stimuli and injury. Glia 59, 869–881 (2011).
Etxeberria, A. et al. Dynamic modulation of myelination in response to visual stimuli alters optic nerve conduction velocity. J. Neurosci. 36, 6937–6948 (2016).
McKenzie, I. A. et al. Motor skill learning requires active central myelination. Science 346, 318–322 (2014).
Zatorre, R. J., Fields, R. D. & Johansen-Berg, H. Plasticity in gray and white: neuroimaging changes in brain structure during learning. Nat. Neurosci. 15, 528–536 (2012).
Schain, A. J., Hill, R. A. & Grutzendler, J. Label-free in vivo imaging of myelinated axons in health and disease with spectral confocal reflectance microscopy. Nat. Med. 20, 443–449 (2014).
Hill, R. A. & Grutzendler, J. In vivo imaging of oligodendrocytes with sulforhodamine 101. Nat. Methods 11, 1081–1082 (2014).
Safaiyan, S. et al. Age-related myelin degradation burdens the clearance function of microglia during aging. Nat. Neurosci. 19, 995–998 (2016).
Lasiene, J., Matsui, A., Sawa, Y., Wong, F. & Horner, P. J. Age-related myelin dynamics revealed by increased oligodendrogenesis and short internodes. Aging Cell 8, 201–213 (2009).
Peters, A. & Kemper, T. A review of the structural alterations in the cerebral hemispheres of the aging rhesus monkey. Neurobiol. Aging 33, 2357–2357 (2012).
Bartzokis, G. Age-related myelin breakdown: a developmental model of cognitive decline and Alzheimer’s disease. Neurobiol. Aging 25, 5–18 (2004).author reply 49–62.
Sturrock, R. R. Age-related changes in the number of myelinated axons and glial cells in the anterior and posterior limbs of the mouse anterior commissure. J. Anat. 150, 111–127 (1987).
Peters, A. & Sethares, C. Aging and the myelinated fibers in prefrontal cortex and corpus callosum of the monkey. J. Comp. Neurol. 442, 277–291 (2002).
Romanelli, E. et al. Myelinosome formation represents an early stage of oligodendrocyte damage in multiple sclerosis and its animal model. Nat. Commun. 7, 13275 (2016).
Kreutzberg, G. W. Microglia: a sensor for pathological events in the CNS. Trends Neurosci. 19, 312–318 (1996).
Bengtsson, S. L. et al. Extensive piano practicing has regionally specific effects on white matter development. Nat. Neurosci. 8, 1148–1150 (2005).
Fields, R. D. A new mechanism of nervous system plasticity: activity-dependent myelination. Nat. Rev. Neurosci. 16, 756–767 (2015).
Hines, J. H., Ravanelli, A. M., Schwindt, R., Scott, E. K. & Appel, B. Neuronal activity biases axon selection for myelination in vivo. Nat. Neurosci. 18, 683–689 (2015).
Mensch, S. et al. Synaptic vesicle release regulates myelin sheath number of individual oligodendrocytes in vivo. Nat. Neurosci. 18, 628–630 (2015).
Peters, A., Verderosa, A. & Sethares, C. The neuroglial population in the primary visual cortex of the aging rhesus monkey. Glia 56, 1151–1161 (2008).
Huang, W. et al. Novel NG2-CreERT2 knock-in mice demonstrate heterogeneous differentiation potential of NG2 glia during development. Glia 62, 896–913 (2014).
Miller, D. J. et al. Prolonged myelination in human neocortical evolution. Proc. Natl Acad. Sci. USA 109, 16480–16485 (2012).
Haroutunian, V. et al. Myelination, oligodendrocytes, and serious mental illness. Glia 62, 1856–1877 (2014).
Power, B. E. et al. Remyelination reporter reveals prolonged refinement of spontaneously regenerated myelin. Proc. Natl Acad. Sci.USA 110, 4075–4080 (2013).
Hill, R. A., Patel, K. D., Medved, J., Reiss, A. M. & Nishiyama, A. NG2 cells in white matter but not gray matter proliferate in response to PDGF. J. Neurosci. 33, 14558–14566 (2013).
Viganò, F., Möbius, W., Götz, M. & Dimou, L. Transplantation reveals regional differences in oligodendrocyte differentiation in the adult brain. Nat. Neurosci. 16, 1370–1372 (2013).
Bechler, M. E., Byrne, L. & Ffrench-Constant, C. CNS myelin sheath lengths are an intrinsic property of oligodendrocytes. Curr. Biol. 25, 2411–2416 (2015).
Howell, O. W. et al. Meningeal inflammation is widespread and linked to cortical pathology in multiple sclerosis. Brain 134, 2755–2771 (2011).
Lucchinetti, C. F. et al. Inflammatory cortical demyelination in early multiple sclerosis. N. Engl. J. Med. 365, 2188–2197 (2011).
Bartzokis, G. et al. Lifespan trajectory of myelin integrity and maximum motor speed. Neurobiol. Aging 31, 1554–1562 (2010).
Yeh, F. L., Hansen, D. V. & Sheng, M. TREM2, microglia, and neurodegenerative diseases. Trends Mol.Med. 23, 512–533 (2017).
Hirrlinger, P. G. et al. Expression of reef coral fluorescent proteins in the central nervous system of transgenic mice. Mol. Cell. Neurosci. 30, 291–303 (2005).
Doerflinger, N. H., Macklin, W. B. & Popko, B. Inducible site-specific recombination in myelinating cells. Genesis 35, 63–72 (2003).
Deng, Y. et al. Direct visualization of membrane architecture of myelinating cells in transgenic mice expressing membrane-anchored EGFP. Genesis 52, 341–349 (2014).
Feng, G. et al. Imaging neuronal subsets in transgenic mice expressing multiple spectral variants of GFP. Neuron 28, 41–51 (2000).
Jung, S. et al. Analysis of fractalkine receptor CX(3)CR1 function by targeted deletion and green fluorescent protein reporter gene insertion. Mol. Cell. Biol. 20, 4106–4114 (2000).
Muzumdar, M. D., Tasic, B., Miyamichi, K., Li, L. & Luo, L. A global double-fluorescent Cre reporter mouse. Genesis 45, 593–605 (2007).
Hill, R. A., Damisah, E. C., Chen, F., Kwan, A. C. & Grutzendler, J. Targeted two-photon chemical apoptotic ablation of defined cell types in vivo. Nat. Commun. 8, 15837 (2017).
Hill, R. A. et al. Regional blood flow in the normal and ischemic brain is controlled by arteriolar smooth muscle cell contractility and not by capillary pericytes. Neuron 87, 95–110 (2015).
We thank A. Nishiyama (University of Connecticut) and F. Kirchhoff (University of Saarland) for sharing PLP-DsRed transgenic mice. This work was supported by the following grants from the National Institutes of Health: R21NS087511, R21NS088411 and R01NS089734 to J.G.; T32NS007224 andT32GM007205 to A.M.L.; and F32NS090820 and K99NS099469 to R.A.H. This work was also supported in part by a research grant from the National Multiple Sclerosis Society (#RR-1602-07686) to J.G. and a New Vision Award through the Donors Cure Foundation to R.A.H.
The authors declare no competing interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Integrated supplementary information
Supplementary Figure 1 Spectral confocal reflection (SCoRe) microscopy allows label-free myelin imaging in vivo and in fixed tissues.
(a) In vivo image captured from layer I of the mouse somatosensory cortex showing the separated reflective wavelengths of single myelin fibers using SCoRe microscopy. All other SCoRe images were combined into a single color. (b) In vivo image of an oligodendrocyte in the cortex of a transgenic mouse with DsRed fluorescent protein expressed exclusively in mature oligodendrocytes (Plp-DsRed) showing the specificity of the SCoRe signal for portions of the oligodendrocyte forming compact myelin (arrows) and not the proximal processes extending from the oligodendrocyte cell body (arrowheads). (c) Confocal images in fixed brain slices showing the overlap of SCoRe signal with that of immunofluorescence for myelin basic protein (MBP). (d) Confocal images showing the beginning portion of myelination at the axon initial segment (AIS) visualized with SCoRe microscopy and with MBP staining in the top image (arrow) as well as a break in myelination at a node of Ranvier in the bottom image (arrowhead). Each image is representative of at least three locations in at least three animals.
Supplementary Figure 2 Overlap between fluorescent and SCoRe signals for in vivo detection of myelin.
(a) In vivo image captured from layer I of the somatosensory cortex in a transgenic mouse with membrane tethered EGFP expressed exclusively in mature oligodendrocytes (Cnp-mEGFP) showing the overlap between fluorescence and SCoRe. Single oligodendrocyte cell soma can be seen in the fluorescence (yellow arrowheads) but not the SCoRe image due to the specificity of SCoRe for myelin. (b) The number of myelin segments intersecting the yellow line can be quantified as a proxy for equivalent myelin detection between mEGFP and SCoRe as shown in Fig. 1g. (c) Reliable detection of myelin segment borders (arrowheads) using both fluorescence and SCoRe as shown in Fig. 1g. (d) Classification of myelin segments as paired or unpaired for quantification of internode plasticity as shown in Fig. 3h-i. Each image is representative of at least three locations in at least three animals.
(a) Oligodendrocyte (Plp-DsRed) and SCoRe imaging captured in vivo from the somatosensory cortex at the ages indicated showing significant changes in both oligodendrocyte cell soma and myelin fiber density. Each image is representative of at least three locations in at least three animals.
(a) Images of oligodendrocyte specific CNPase staining captured from the somatosensory cortex showing age-dependent changes in the upper layers of the cortex. (b) Examples of single oligodendrocyte cell soma (arrows) revealed by CNPase staining in layer I of the cortex. Each image is representative of at least three locations in at least three animals.
(a) In vivo time-lapse SCoRe images showing addition of single myelin internodes (yellow arrows) and extension of a single myelin internode (yellow arrowhead) over 68 days (b) In vivo two-photon fluorescence images of a single oligodendrocyte (red arrow) imaged over 60 days in a transgenic mouse (Plp-creER:mT/mG) with membrane tethered GFP expressed specifically in mature oligodendrocytes and membrane tethered Tomato (mTomato) expressed predominantly in cerebral blood vessels. (c-d) In vivo time-lapse images showing extension of single internodes (blue arrowheads) and stability of other internodes from the same oligodendrocyte (red arrowheads). Each image is representative of at least three locations in at least three animals.
(a) In vivo images captured from the cortex of a P60 Thy1-YFP transgenic mouse showing a partially myelinated axon with arrowheads designating myelin segments and arrows pointing to unmyelinated regions. (b) Image captured from the cortex of a P640 mouse showing an unmyelinated region along a single axon in late adulthood. (c) Representative traced axons from mice at the ages indicated showing age-dependent increase in myelin coverage along single axons. Each image is representative of at least three locations in at least three animals.
(a-b) In vivo images captured from the cortex of a 910-day old mouse with mature oligodendrocytes labeled with DsRed (Plp-DsRed) showing examples of myelin pathology detected in aged mice revealed by SCoRe and DsRed fluorescence. Myelin spheroids (yellow arrowheads) can be detected using SCoRe and are only found in aged mice. Myelin debris (yellow arrows) can also be detected using SCoRe and the vast majority were found to have accumulation of DsRed fluorescent protein in the Plp-DsRed transgenic mice. Myelin debris and oligodendrocyte cell bodies (white arrows) can be distinguished due to the lack of SCoRe signals in addition to the proximal processes extending from the cell body. (c) In vivo image captured from the cortex of a Cx3cr1-GFP:Plp-DsRed transgenic mouse showing accumulation of reflective and DsRed labeled myelin debris within microglia (yellow arrows). (d) High resolution in vivo image of a single myelin debris accumulation engulfed within a microglia process (e–g) In vivo images showing examples of myelin debris engulfed by microglia (yellow arrows) with no preferential microglial association with myelin spheroids (yellow arrowheads). Each image is representative of at least three locations in at least three animals.
Low magnification in vivo image captured from the cortex of a Cx3cr1-GFP:Plp-DsRed transgenic mouse showing the capabilities of imaging myelination (SCoRe), oligodendrocytes (Plp-DsRed) and microglia (Cx3cr1-GFP) in an 810 day old mouse. This image is representative of at least three locations in at least three animals.
(a) Image captured of a tissue section stained with nuclear dye from an 860-day old Cx3cr1-GFP:Plp-DsRed transgenic mouse showing myelin debris accumulation (white arrows) within a single microglia. These debris are characterized by bright DsRed and SCoRe labeling and no nuclear dye labeling. Two oligodendrocyte cell soma are shown in the lower portion of the image characterized by DsRed expression with nuclear dye labeling. (b) Images from 860-day old Cx3cr1-GFP:Plp-DsRed mice showing the presence of myelin debris within microglia in the cerebral cortex, corpus callosum, and the hippocampus suggesting myelin degeneration is a wide spread phenomenon in the aging brain. Each image is representative of at least three locations in at least three animals.
Supplementary Figures 1–9
Descriptive statistics for all data
Supplementary Video 1 – Overlap between fluorescent and SCoRe signals for in vivo detection of myelin
Video shows a confocal Z stack taken through a cranial window of an anesthetized transgenic mouse with membrane tethered EGFP expressed exclusively in mature oligodendrocytes (Cnp-mEGFP) overlaid with sequentially acquired SCoRe signals. White arrow indicates a mEGFP labeled cell body and yellow arrows indicate the location of a presumptive node of Ranvier as evidenced by the break in both fluorescence and SCoRe signals. Depth from the pial surface is indicated in the upper right corner. This video is representative of at least three locations in at least three animals.
Video shows two time-lapse sequences of microglia process surveillance in an 810 day old Cx3cr1-GFP:Plp-DsRed transgenic mouse. Time is indicated in the upper right corner. This video is representative of at least three locations in at least three animals.
About this article
Cite this article
Hill, R.A., Li, A.M. & Grutzendler, J. Lifelong cortical myelin plasticity and age-related degeneration in the live mammalian brain. Nat Neurosci 21, 683–695 (2018). https://doi.org/10.1038/s41593-018-0120-6
Myelin and oligodendrocyte lineage cell dysfunctions: New players in the etiology and treatment of depression and stress‐related disorders
European Journal of Neuroscience (2021)
Building a (w)rapport between neurons and oligodendroglia: Reciprocal interactions underlying adaptive myelination
Oxidative stress and impaired oligodendrocyte precursor cell differentiation in neurological disorders
Cellular and Molecular Life Sciences (2021)