Study reveals impact of oft-overlooked cell in brain function

Washington DC [US], May 17 : An often-ignored type of cell in the brain plays a dynamic and surprisingly complex role in our ability to process information, according to new research from Oregon Health & Science University (OHSU).

The study, published today in the journal Science, provides direct evidence for the real-time action of a star-shaped type of glial cell, known as astrocytes, in the live brains of fruit flies

The abundant cell type roughly 35% of all cells in the human brain appears to be a key part of orchestrating a complex network governing brain function.

"We hope this begins to fundamentally change how the field thinks about astrocytes and their role in mediating neurophysiology and behaviour," said senior author Marc Freeman, Ph.D., director of the OHSU Vollum Institute. "

Over the long run, it should change how people think about developing therapies for regulation of attention, anxiety and mood," he added.

The discovery was replicated in the astrocytes of rodents, suggesting it's an ancient feature of evolution likely to be conserved in other mammals including people.

"I think it's evolutionarily relevant to survival," said lead author Kevin Guttenplan, Ph.D., a postdoctoral scientist in Freeman's lab.

"If a tiger's behind you, you need to rapidly change how whole brain regions are thinking it's time to shut out everything else on your mind and entirely focus the brain on escaping. It's not the time to think about anything else," Kevin added.

At one time, astrocytes were thought to serve only a supporting role by providing food and removing waste for neurons, the cells that form the brain's "hardwiring" by transmitting signals enabling us to think, act and feel sensations.

In 2016, Freeman and collaborators documented for the first time that astrocytes also transmit signals between neurons.

Building on that discovery, researchers show some of the specific mechanisms revealing how those cells transmit signals. It turns out to be a highly complex interplay in which astrocytes can turn on and off their ability to respond to chemical neurotransmitters in the brain, such as dopamine and glutamate.

"Astrocytes are really big, and a single cell can have 100,000 synapses capable of sending signals to other cells," Guttenplan said.

"This mechanism allows them to choose which neurons to listen to. Being able to turn off some of those circuits allows astrocytes to make sense of the cacophony of activity occurring in in the brain from moment to moment," added Guttenplan.

Researchers found that by manipulating this gating pathway within astrocytes, they were able to disrupt the behavior of the fruit flies highlighting the fact that these small changes can have a potent impact.

The new research reveals that astrocytes can directly respond to messages from all types of neurons.

In this way, they play a role in the complex network of neuronal signalling that drives cognition and controls physical behaviour. In addition, they found these responses change dynamically with brain state, allowing astrocytes to orchestrate the complex network of neurons, enabling the brain to attend to the tasks at hand.

"These cells do actively control neuronal activity, really powerfully," Guttenplan said.

However, scientists caution that the discovery complicates scientific understanding of how the brain functions.

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