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news.A recent study has found evidence to implicate astrocytes, a type of brain cell overlooked by much research, in the development of Alzheimer's disease.
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Scientists at the University of Rochester Medical Center have demonstrated that star-shaped brain cells known as astrocytes play a direct role in controlling blood flow in the brain, a crucial process that allows parts of the brain to burst into activity when needed.
The finding is intriguing for a disease like Alzheimer’s, which has long been considered a disease of brain cells known as neurons, and certainly not astrocytes.
“In a disease like Alzheimer’s, for instance, perhaps it’s the astrocytes themselves that are damaged first,” said Dr Maiken Nedergaard professor in the Department of Neurosurgery at Rochester. “It may be that for whatever reason, astrocytes are not doing their job properly, and then blood flow decreases. This could lead to the death of the neurons, which would starve from a lack of nutrients, since the neurons depend on the astrocytes for their survival.”
Most scientists have assumed that the more blood that flows to a particular part of the brain, the more activity on the part of neurons, the nerve cells that send electrical signals that are widely considered to be “brain activity.” However, this research has thrown doubt on this 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.”
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 the new results muddy the picture, calling into question any straightforward link between the health of neurons and blood flow.