This LiveScience article reviews some recent research.
A new study finds that a cell once believed to serve neurons instead may perform the crucial function of regulating blood flow in the brain.
The discovery challenges a basic assumption in neuroscience and could have implications for interpreting brain scans and understanding what occurs during brain trauma and Alzheimer's disease.
Neuroscientists have long known astrocytes help to support neurons. Wikipedia is terser than the neuroscience text on my shelf, but it will serve:
Astrocytes are sub-type of the glial cells in the brain. They are also known as astrocytic glial cells. Star-shaped, their many arms span all around neurons. They outnumber the neurons ten to one. Astrocytes are classically identified histologically by their expression of glial fibrillary acidic protein (GFAP). Previously in medical science, the neuronal network was considered the only important one, and astrocytes were looked upon as gap fillers. But recently they have been reconsidered and are now thought to play a number of active roles in the brain.
The current research has found that astrocytes can regulate blood flow themselves with no neural involvement:
Recent experiments, however, revealed that astrocytes form connections with blood vessels and control the flow of nutrients, including oxygen, to neurons. When brain activity increases, neurons trigger astrocytes to release calcium, which in turn affects other chemical messengers that can cause blood vessels to either dilate or contract.
From start to finish, the process takes about 1 second.
"That's amazing; no other organs can increase their blood flow so fast," Nedergaard said.
While neurons and astrocytes usually work closely with one another, the new finding raises the possibility that there may be times when astrocytes increase blood flow on their own without any prompting from neurons.
The article discusses the possibility that Alzheimer's may be initiated by astrocyte malfunction rather than neuron death.
Reading it, I wonder whether it is neuroscience or genomics that poses the greatest unsolved problems right now. I guess studying the evolution of the brain tends to stack both sets right on top of each other.