Astrocytes are star shaped cells that make up around 35% of human brain cells. They were once thought of as cells that simply supported neurons in the central nervous system (CNS). But in recent years, scientists have uncovered many important roles for astrocytes that has elevated them from mere supporting players; their crucial functions are being increasingly identified and recognized. Several new studies have shown how astrocytes help regulate the activity of neurons and synapses--critical junctions where neurons meet and signal to one another.
Neurotransmitters allow individual neurons to communicate rapidly, while neuromodulators can impact whole populations of neurons to alter neuronal activity much more slowly. New research reported in Science has shown how neuromodulators link with neurons, and astrocytes are crucial to this process.
By understanding the system of neuromodulation, we may be able to open up new treatment avenues for mental conditions, the researchers noted.
“Including these pathways more frequently in studies of psychiatric conditions makes a lot of sense,” noted senior study author and Janelia Senior Group Leader Misha Ahrens. “Knowing that a lot of the neuromodulation underlying brain function and dysfunction flows through astrocytes supports considering this new cell group as a potential therapeutic target."
Another study reported in Science by a different group of researchers has shown how astrocytes help govern the function of the brain. Around 2016, this group discovered that astrocytes can also send signals to neurons. This latest study has revealed some of the mechanisms astrocytes use to send those signals.
Astrocytes were shown to be able to react directly to various signals from different kinds of neurons, and in doing so, they are related to a complex network in which neurons control behavior and cognition. The astrocytes' response to neuronal signals can also change; they can modulate how they respond to neurotransmitters 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,” explained first study author Kevin Guttenplan, Ph.D. “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.”
“We hope this begins to fundamentally change how the field thinks about astrocytes and their role in mediating neurophysiology and behavior,” added senior study 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.”
There was also another study reported in Science that demonstrated how neuromodulation in the hippocampus can occur. In a mouse model, norepinephrine can affect astrocytes in the hippocampus, which impacts neuronal signaling.
A perspective written in Science that covers many of these findings has a title that shows how important astrocytes are: "Astrocytes, hidden puppet masters of the brain."
The role of astrocytes in the brain appears to be essential to neuromodulation in various species and across different kinds of neural circuits and behavioral processes.
Sources: Howard Hughes Medical Institute Janelia Research, Oregon Health & Science University (OHSU), Guttenplan et al Science 2025, Chen et al Science 2025