Blood Flow In Brain Takes A Twist, Affecting Views Of Alzheimer's

New findings that long-overlooked brain cells play an important role in regulating blood flow in the brain call into question one of the basic assumptions underlying today's most sophisticated brain imaging techniques and could open a new frontier when it comes to understanding Alzheimer's disease.

Now the group led by Nedergaard, professor in the Department of Neurosurgery and a member of the Center for Aging and Developmental Biology, and post-doctoral associate Takahiro Takano, Ph.D., the first author of the paper, has thrown doubt on the assumption by showing that astrocytes are important players in the process too. Studies by the team in mice show that signaling from astrocytes causes arteries in the brain to expand, bringing about an increase in blood flow. "When we measure blood flow," said Nedergaard, "it may be that we are not measuring the activity of neurons so much as that of astrocytes." The idea creates a "chicken or egg" type question in patients with conditions like Alzheimer's or traumatic brain injury where blood flow to parts of the brain plummets. In Alzheimer's it's known that neurons sicken and die over a period of years. To diagnose the disease, doctors often order a brain scan. When the test shows lessened blood flow, doctors assume that there must be less of a demand for blood, and so significant numbers of neurons in that brain region must have died. While that still may be true, Nedergaard said, the new results muddy the picture, calling into question any straightforward link between the health of neurons and blood flow. Nedergaard said that while it is new to find that astrocytes can regulate blood flow, the finding shouldn't be entirely surprising. She said that astrocytes physically touch both synapses - the spaces between neurons that are crucial to brain activity - and blood vessels. In fact, "footprints" of astrocytes are literally all over blood vessels in the brain: Portions of astrocytes known as "astrocytic endfeet" wrap around nearly all the blood vessels in the brain.

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