For decades, neurons have hogged the spotlight, both among brain researchers and laypeople, who might think all brain cells are neurons.
In fact, more than half the brain is made of glial cells.
Chris Dulla, the Annetta and Gustav Grisard Chair and Professor of Neuroscience at Tufts University School of Medicine, thinks it’s time to turn our collective attention to a type of glial cell called astrocytes.
“I want to push people to reimagine how these cells function,” Dulla said. “We have new tools and creative researchers. We can change and innovate how we think about astrocytes.”
Rethinking how astrocytes function could open a whole new area for developing therapies for diseases of the brain, from epilepsy to Alzheimer’s disease.
To encourage brain researchers worldwide to plumb the mysteries of astrocytes, Dulla and a group of international colleagues recently published a paper in Nature Neuroscience summarizing what’s known about astrocytes and laying out big unanswered questions.
Astrocytes, which Dulla describes as “fluffy stars,” have numerous thread-like branches extending out from a central core. For decades after their discovery in the mid-1800s, scientists thought astrocytes and other glial cells did little more than provide structure for the neurons.
More recently, scientists have shown that astrocytes control blood flow and metabolism in the brain, helping to maintain a steady state and support the function of neurons.
“We’re learning that astrocytes play a role in memory formation, mood, and attentional state,” Dulla said. “They contribute to sleep, wakefulness, anxiety, depression, and lots of different diseases.”
Dulla also suspects that astrocytes may be key to brain plasticity—the brain’s ability to change in response to an injury or learning something new. Understanding the full extent of how astrocytes function could open a host of targets for developing drugs for traumatic brain injury, epilepsy, dementia, and more.
Challenging Long-Held Beliefs
Dulla believes that scientists have only scratched the surface of understanding the role of astrocytes in the brain. “Everyone who is interested in glial biology is open to exploring new ideas to figure out what we’ve been missing,” he said.
For example, he said, “People thought for a hundred years that astrocytes were not electrically active. We showed that they are.”
Neurons send electrical signals among individual cells, but astrocytes connect to each other across large areas of the brain, forming a kind of mesh or net of electrical activity.
In another example, Dulla said recent research is challenging long-held notions that all astrocytes have the same job. “Astrocytes are quite different,” he said. “Some might be playing a role in a certain brain function, and others in a totally different function.”
Evolutionary Clues?
In addition to opening avenues for drug discovery, astrocytes may provide important clues about the evolution of the human brain.
“Neurons don’t change much between species, but astrocytes do,” Dulla said, noting that mice astrocytes are simple, monkey astrocytes are more complicated, and human astrocytes are the most complex. “Is that what allows our brains to be more elegant and sophisticated and complex?”
To understand why human astrocytes are so complex, scientists must first tease out the functional meaning of the astrocyte’s structure: What do the branches do? Why does the number of branches vary? Do different branches have different tasks?
Tufts is a natural home for asking and answering these kinds of questions.
“Tufts has been a leader and innovator in glial biology going back to Phil Haydon, the previous chair of the neuroscience department and a pioneer in the field,” Dulla said. “He brought in people interested in glial biology, and we continue to develop that area.”
Dulla is looking forward to more discoveries, at Tufts and elsewhere, about astrocytes. “Astrocytes are doing something neurons can’t do,” he said. “They do their own types of computation that are different and complementary to how neurons do it. They form a completely different layer or system of the brain that’s functioning on a different time and spatial scale than we have ever thought about before.”
by Mary-Russell Roberson