Glial cells, which help neurons communicate with each other, can leave the central nervous system and cross into the peripheral nervous system to compensate for missing cells, according to new research in the Dec. 2 issue of The Journal of Neuroscience. The animal study contributes to researchers' basic understanding of how the two nervous systems develop and are maintained, which is essential for the effective treatment of diseases such as multiple sclerosis. This time-lapse video shows oligodendrocytes cross the glial barrier and myelinate moto axons in mutant zebrafish that lack Schwann cells. Credit: Appel et al./Society for Neuroscience