Glial cells control sleep and metabolism

Fruit flies, despite their tiny brains, sleep almost like humans, and their simplicity makes them ideal for science. “We spend a third of our lives sleeping, but we still don’t know why we need it,” says Andres Flores-Valle, lead author of the project. His team looked for a signal in the flies’ brains that indicates when it’s time to rest. This signal should rise when the fly is tired and fall after a sound sleep, like a fatigue meter.

To catch this signal, the scientists monitored the activity of cells in the flies’ brains under a microscope. They created comfort for the insects: they fed them every couple of hours with the help of a robot and let them sleep directly under the lenses. For the first time, they were able to record what goes on in the flies’ heads for days on end while they are awake or napping. The focus was on two types of glia: astrocyte-like cells that keep brain chemistry in order, and envelope cells that repair damaged nerves and scavenge debris.

The glial cells were surprising: they monitored the need for sleep through calcium signaling. When the fly was awake and moving, these signals rose, and in sleep they fell off, as if resetting the meter. But that wasn’t all – neurons thought to control sleep were instead monitoring hunger. And calcium in the glia turned out to be linked to metabolism: it helped eliminate carbon dioxide and keep the brain’s acidity normal. So sleep is needed to give the body a break and restore balance.

The discovery hints: glia are not just helpers, but conductors of sleep and appetite. Their metabolic response affects how the fly sleeps and eats. This opens the door to new questions: how do these cells turn on sleep? How do their signals walk around the brain? The answers could open a new perspective on sleep mechanisms, helping us understand why we need rest and how to treat metabolic malfunctions or insomnia.