Length of myelin internodes of individual oligodendrocytes is controlled by microenvironment influenced by normal and input-deprived axonal activities in sensory deprived mouse models.

Oligodendrocytes myelinate neuronal axons to increase conduction velocity in the vertebrate central nervous system (CNS). Recent studies revealed that myelin formed on highly active axons is more stable compared to activity-silenced axons, and length of the myelin sheath is longer in active axons as well in the zebrafish larva. However, it is unclear whether oligodendrocytes preferentially myelinate active axons compared to sensory input-deprived axons in the adult mammalian CNS. It is also unknown if a single oligodendrocyte forms both longer myelin sheaths on active axons and shorter sheaths on input-deprived axons after long-term sensory deprivation. To address these questions, we applied simultaneous labeling of both neuronal axons and oligodendrocytes to mouse models of long-term monocular eyelid suturing and unilateral whisker removal. We found that individual oligodendrocytes evenly myelinated normal and input-deprived axons in the adult mouse CNS, and myelin sheath length on normal axons and input-deprived axons formed by a single oligodendrocyte were comparable. Importantly, the average length of the myelin sheath formed by individual oligodendrocytes did change depending on relative abundance of normal against sensory-input deprived axons, indicating an abundance of deprived axons near an oligodendrocyte impacts on myelination program by a single oligodendrocyte.