Rabies virus-mediated oligodendrocyte labeling reveals a single oligodendrocyte myelinates axons from distinct brain regions.

Oligodendrocytes myelinate neuronal axons during development and increase conduction velocity of neuronal impulses in the central nervous system. Neuronal axons extend from multiple brain regions and pass through the white matter; however, whether oligodendrocytes ensheath a particular set of axons or do so randomly within the mammalian brain remains unclear. We developed a novel method to visualize individual oligodendrocytes and axon derived from a particular brain region in mouse white matter using a combinational injection of attenuated rabies virus and adeno-associated virus. Using this method, we found that some populations of oligodendrocytes in the corpus callosum predominantly ensheathed axons derived from motor cortex or sensory cortex, while others ensheathed axons from both brain regions, suggesting heterogeneity in preference of myelination toward a particular subtype of neurons. Moreover, our newly established method is a versatile tool for analyzing precise morphology of each oligodendrocyte in animal models for demyelinating disorders and addressing the role of oligodendrocyte in higher brain functions. GLIA 2016. GLIA 2017;65:93-105.