Figure 1.

Color illustration depicting the “NVU” in both gray and white matter of the human brain. In white matter, both astrocytes and oligodendrocytes are involved in the NVU, since a major part of the neuronal axon is myelinated by oligodendrocytes. Importantly, however, astrocytes can contact axons directly at the site of the Ranvier node. Note that it has not been reported that oligodendrocytes have direct contact with microvessels, since astrocytic endfeet cover microvessels almost completely. Therefore, astrocytes contact oligodendrocytes as well as axons. One of the important roles of astrocyte is the regulation of synaptic transmission. The endfeet of astrocytes envelope synapses (i.e., tripartite synapse). Moreover, astrocytes connect themselves with connexin gap junctions, forming a huge syncytium. At present, the anatomical location of microglia in the NVU is not specified.