If you’re feeling sleepy, it might be thanks to your astrocytes. This group of brain cells, long assumed to play a mere housekeeping role, may actually be responsible for controlling when we fall asleep, by releasing a chemical called adenosine.
“One of the leading theories of sleep generation comes from the observation that there is an accumulation of adenosine [in the brain] during waking, and that this adenosine decreases during subsequent sleep,” says Tommaso Fellin at the Italian Institute of Technology in Genoa. Adenosine is thought to suppress neurons which usually stimulate the cortex and keep it, and so us, awake. However, he says, “the cellular source of this adenosine has long been overlooked”.
Astrocytes play a key role in providing neurons with nutrients and aiding cell repair. In addition, unlike neurons that control immediate brain activity, astrocytes are thought to modulate longer-term activity by regulating communication between neurons. Because sleep pressure – the physiological mechanisms that result in the need to sleep – also builds up over a prolonged period of time, Fellin and Michael Halassa, now at the Massachusetts Institute of Technology, and colleagues, decided to investigate whether astrocytes might be the source of the adenosine that may drive the urge to sleep.
They used mice which had been genetically engineered to stop releasing adenosine from their astrocytes in response to an antibiotic in their food. Suppressing levels of adenosine reduced the length of sleep the mice took after being deprived of shut-eye for 6 hours, and prevented some of the cognitive defects associated with sleep loss (Neuron, DOI: 10.1016/j.neuron.2008.11.024).
“Our research suggests that these cells are responsible for adenosine accumulation” and the regulation of sleep, says Fellin, who presented the results at the Forum of European Neuroscience in Amsterdam, the Netherlands, last week.
“This is exactly the type of function that astrocytes would be expected to perform,” says Douglas Fields at the US National Institutes of Health in Bethesda, Maryland. “Astrocytes communicate slowly and on larger spatial scales than neurons. They are well suited to have a more global influence on brain function.”
By: Linda Geddes / Courtesy: New Scientist