Researchers have mapped 3D networks of support cells in the mouse brain for the first time, revealing long-range connections between distant regions and between the two hemispheres.
For many years, neurons have been the center of brain research, while astrocytes—star-shaped support cells that fill the spaces between nerve cells—have been seen primarily as auxiliary forces. Now, researchers are presenting findings that challenge this view: Astrocytes in the mouse brain do not act only locally, but form extensive networks that connect distant regions of the brain, and even between the two hemispheres.
The study, published in Nature, involved constructing a complete 3D map of astrocyte networks in the brain—the first of its kind, the researchers say. The map shows that astrocytes are connected to each other by tiny communication nodes, called gap junctions, that allow molecules such as calcium and glucose to pass between neighboring cells. Although each astrocyte does not have long extensions like the axons of neurons, chains of connected cells can form “communication lines” that extend over considerable distances in the mouse cerebellum.
The significance of the finding is twofold. First, it shows that, alongside the familiar neuronal networks, there is also another, more hidden communication system in the brain, based on glial cells. Second, it raises the possibility that astrocytes not only clean up chemical "waste" and provide nutrients to neurons, but also participate in information transmission, metabolic coordination, and perhaps even shaping brain activity on a large scale. One of the authors of the article described this system as "a kind of secret subway" that was operating in the brain all the time, but until now we were unaware of its existence.
To uncover these networks, the researchers injected specific areas of the brains of mice with a genetic system that allowed astrocytes to "stamp" molecules that pass through the junctions between them. This made it possible to retrospectively track all astrocytes connected to a network originating in a specific area. The results surprised the researchers: alongside small, local networks within a given brain region, connections were also found that crossed different regions, stretched for centimeters, reached the brainstem, and even bridged the hemispheres of the brain.
The study also showed that astrocyte networks are not fixed and rigid. When the researchers created sensory deprivation in mice by clipping their whiskers – a common model for studying brain plasticity – they found that astrocyte networks also changed and rebuilt. That is, similar to neural networks, the astrocyte system also responds to changes in sensory input and reorganizes itself. This finding strengthens the hypothesis that these cells play an active role in brain plasticity, and not just a maintenance role.
The function of astrocyte pathways is unclear.
The exact function of these “astrocyte highways” is still unclear. One hypothesis put forward by researchers is that the networks serve to transport metabolites from less active to more active areas, thus helping to balance energy consumption in the brain. Other researchers believe that the finding opens the door to a broader understanding of how astrocytes “listen” to neuronal activity, process it, and influence nerve cells back. If so, the brain may operate using two integrated layers of communication: one neural, fast and electrical, and one glial, chemical and more spatial.
The findings may also have implications for the study of neurological and psychiatric diseases. If astrocytes connect distant regions and participate in brain plasticity, disruption of these networks may play a role in diseases in which communication between brain regions is impaired. At this stage, this is still basic research in mice, and the researchers emphasize that many more questions remain than answers. However, one of the researchers estimated that it is likely that the general principle also applies to other animals, including primates.
The bottom line is that this study reminds us that the brain is much more than the classic picture of neurons alone. Astrocytes, long considered “minor players,” are now emerging as part of a vast, dynamic, and ever-changing communication system. If the findings hold true in more complex brains, we may have to rewrite some of our understanding of how the brain is organized—and who is actually participating in the constant internal conversation that goes on inside it.
More of the topic in Hayadan:
