Johns Hopkins University scientists have created detailed, brain-wide maps of mouse brains, pinpointing the location of over 10 million oligodendrocytes – the cells responsible for forming myelin, the protective sheath around nerve fibers crucial for efficient signal transmission. The research, published February 18 in the journal Cell, offers unprecedented insight into the organization of myelin and its potential role in neurological disorders.
The maps, developed using a combination of 3D imaging, specialized microscopy, and artificial intelligence, reveal how myelin content varies across different brain circuits. Researchers believe this detailed understanding could illuminate the mechanisms behind diseases like multiple sclerosis, Alzheimer’s disease, and other conditions affecting learning, memory, and motor function. While acknowledging differences between mouse and human brains, the team emphasizes shared characteristics and fundamental biological processes.
“Our study identifies not only the location of oligodendrocytes in the brain, but similarly integrates information about gene expression and the structural features of neurons,” explained Dwight Bergles, Ph.D., the Diana Sylvestre and Charles Homcy Professor in the Department of Neuroscience at the Johns Hopkins University School of Medicine. “It’s like mapping the location of all the trees in a forest, but also adding information about soil quality, weather and geology to understand the forest ecosystem.”
The newly created maps offer higher resolution and broader coverage of gray matter – the brain region responsible for processing information – than previously available datasets. Myelin is often difficult to visualize in gray matter using conventional techniques like MRI, making this detailed mapping particularly significant.
“Because myelin can speed communication between neurons, these maps of regional differences in myelin patterning may help us understand how different parts of the brain accomplish different tasks,” Bergles said.
The research team, led by Bergles and first author Yu Kang T. Xu, a Ph.D. Student and Kavli Neuroscience Discovery Institute fellow, collaborated with biomedical engineers and computer scientists to develop a novel imaging pipeline. This involved a tissue-clearing process to remove fatty deposits obstructing deep brain visualization, coupled with light-sheet microscopy for rapid, whole-brain scanning. Machine learning algorithms were then employed to automatically identify and map each oligodendrocyte within the images.
The maps chart oligodendrocyte positions across the mouse lifespan, from two to twenty-four months. The study found that while the number of oligodendrocytes generally increased with age, the rate of formation varied significantly between brain regions. Regions exhibiting slow initial growth maintained a consistently slow rate, suggesting a predetermined developmental program governs myelin patterning.
“It will be interesting to use this approach to see how different life experiences, such as stress, social interaction, and learning affect these patterns,” Bergles noted.
Prolonged oligodendrocyte and myelin formation was observed in brain areas critical for learning and memory, such as the hippocampus. Brain regions directly receiving sensory input contained three times more oligodendrocytes than areas like the primary motor cortex. Researchers hypothesize this difference reflects the brain’s need for faster signal transmission in areas processing sensory information – touch, sound, and sight – with greater speed.
In experiments involving mice exposed to chemicals that destroy oligodendrocytes and myelin, the team identified regions exhibiting varying degrees of vulnerability and resilience. These findings could provide clues for preserving myelin in diseases like multiple sclerosis, according to the researchers. A separate experiment, utilizing a mouse model of Alzheimer’s disease, revealed myelin damage not only near amyloid-beta plaques – a hallmark of the disease – but also in white matter regions with diffuse plaques, suggesting widespread oligodendrocyte dysfunction in Alzheimer’s.
The oligodendrocyte maps are available for free access by other scientists, with the hope of accelerating further discoveries. The work was supported by grants from the National Institutes of Health (AG072305, NS041435, 32GM136577), the Chan Zuckerberg Initiative, the Dr. Miriam and Sheldon G. Adelson Medical Research Foundation and the Kavli Neuroscience Discovery Institute.