In myelination, oligodendrocyte processes enwrap sections of axons termed internodal regions. Little is known about how newly generated oligodendrocytes integrate into mature existing circuits or how environmental changes affect myelination. Hill et al. used spectral confocal reflectance microscopy to monitor oligodendrocyte production and axon myelination over the lifetime of mice. New oligodendrocytes continued to be produced and new internodes continued to be formed on partially myelinated and unmyelinated axons into adulthood. In aged mice, myelination declined and internodes were lost through oligodendrocyte cell death and myelin degeneration. In another study, Hughes et al. used in vivo two-photon imaging of the somatosensory cortex of adult transgenic mice in which oligodendrocyte precursors could be distinguished from mature oligodendrocytes. Consistent with Hill et al., they found that myelination of partially myelinated or unmyelinated axons continued into adulthood and was achieved exclusively by newly generated oligodendrocytes. Interestingly, exposure to an enriched sensory environment markedly increased oligodendrocyte integration into existing circuits. Thus, in mice, myelination by new oligodendrocytes continues in adulthood and is enhanced on exposure to enriched environment, supporting a possible role in circuit plasticity in the adult brain.
Hill, R. A., Li, A. M. & Grutzendler, J. Lifelong cortical myelin plasticity and age-related degeneration in the live mammalian brain. Nat. Neurosci. https://doi.org/10.1038/s41593-018-0120-6 (2018)
Hughes, E. G. et al. Myelin remodeling through experience-dependent oligodendrogenesis in the adult somatosensory cortex. Nat. Neurosci. https://doi.org/10.1038/s41593-018-0121-5 (2018)