Nearly a century after the discovery of strange star-shaped cells in the brain, scientists say they have finally begun to unravel their function.

Researchers from the Massachusetts Institute of Technology report in Science that it appears astrocytes—named for their stellar form—provide nerve cells (neurons) with the energy they need to function and communicate with one another, by signaling blood to deliver the cell fuels glucose and oxygen to them.

When astrocytes were first discovered, it was believed that they were bit players in the brain. But the new research indicates they may actually be major operators that, when out of whack, may help trigger mental disorders such as autism and schizophrenia.

Study coauthor Mriganka Sur, a neuroscientist and head of MIT's Department of Brain and Cognitive Science, says his team saw astrocytes in action while examining brain activity in ferrets.

Using technology called two-photon microscopy, Sur and his colleagues observed that astrocytes in the visual cortex (part of the brain responsible for vision) activated and blood flow increased to nerve cells just seconds after the neurons had fired or sent out signals.

Sur believes the astrocytes—which are as plentiful in the brain as neurons—may control the strength and length of nerve cell communications. Consequently, he says, if astrocytes fail, so, too, may nerve cell connections, potentially leading to still largely unexplained neurological disorders.

"A great many genes that have been linked to autism and schizophrenia are likely to be active in astrocytes," Sur says. "We believe astrocytes will have a huge role in understanding certain brain diseases."

He says astrocytes may also shed light on brain activity captured on scans such as fMRIs (functional magnetic resonance imaging), which measure blood flow allowing scientists to diagnose strokes (areas that are deprived of blood or oxygen) and regions activated during tasks and activities from solving problems to daydreaming.

The reason, according to a Science editorial by neuroscientists Fred Wolf and Frank Kirchhoff of Germany's Max Planck Institute: the findings indicate fMRI "reflects the responses of both cell populations [neurons and astrocytes] in the brain."

Sur says that when the team blocked astrocytes, blood flow did not increase to firing neurons. That means, he says, that "[fMRI is] really measuring astrocyte activation. Thus, anything that influences astrocytes is likely to influence fMRI readings."

4 Comments

1. 1. John_Toradze 04:09 AM 6/21/08

   I remember a note that the only unusual feature of Einstein's brain was a higher than normal number of astrocytes. I think that's correct. it has been a few decades since I read that.

   Reply | Report Abuse | Link to this

2. 2. redfoxone 12:46 PM 6/21/08

   Blood flow is good. Real good. Without blood flow we have a problem.
   http://www.FireMe.To/udi

   Reply | Report Abuse | Link to this

3. 3. natikaal 04:03 PM 6/21/08

   I have always been curious as to how they could possibly know what someone's brain is made up of. At least a person who has been dead for so long, anyway. But you brought up a very interesting and thought-provoking topic.

   Reply | Report Abuse | Link to this

4. 4. John_Toradze 03:18 AM 6/22/08

   > I have always been curious as to how they could possibly know what someone's brain is made up of. At least a person who has been dead for so long, anyway.
   
   Almost all tissue that is looked at with a microscope is dead. A typical way to process it is to freeze it at -80C in a polymer and then make ultra-thin slices with a microtome. A microtome is like one of those meat slicers at the meat counter where they slide a large sausage over it and a thin slice, like bologna falls out. Except a microtome does it so thin that it is around the thickness of a hair or even much less.
   
   There are ways besides freezing to preserve tissue so that it can be examined this way. Formalin (popularly known as formaldehyde) creates cross-links between molecules in the cells so that they don't come apart and bacteria can't eat them. This makes things stay in the same place (mostly) when they are cut.
   
   After cutting, the ultra-thin slice is put onto a microscope slide. Then different methods are used to stain things on the slide so that you can see things. Some stains are red, some blue, or other colors. Some stains are fluorescent and glow in every color of the rainbow. A very useful method to tell things apart (which isn't easy) is to use antibodies that have a stain attached to them. This is very specific, and this way you can be sure of what you are looking at.
   
   The astrocytes though, are pretty easy to see. They have a very different shape from the nerve cells and glial cells in the brain. A little general staining and that's all you really need. That's why we could name them quite a long time ago using the basic methods first developed.
   
   In the case of Einstein, it was removed and preserved in formalin by Dr. Harvey who did the autopsy. It is now at Princeton according to quick web search. Those also say that his brain had more glial cells, but I could swear it was also astrocytes.

   Reply | Report Abuse | Link to this