Scientists have come one step closer to understanding sleep. Researchers have found a group of neurons that act as a sleep homeostat, triggering either sleep or wakefulness depending on activation. The findings are in a paper just published in the journal Nature.
Sleep has always been a bit of a mystery to the scientific community. The act of sleeping leaves animals vulnerable to predators and other dangers. The exact benefits of sleep are unknown but it seems to be very important for maintaining homeostasis in the body. Two major systems control sleep in animals. The circadian clock tracks environmental changes and helps induce sleep at appropriate times. The other system, the sleep homeostat, is the “switch” that makes us fall asleep or wake up. The sleep homeostat is poorly understood and was the focus of the study.
Researchers from Oxford University used fruit flies to study the sleep homeostat. Fruit flies have a cluster of neurons that control sleep functions. Humans are believed to have a similar set of neurons in the brain, making fruit flies valuable models for studying the mechanisms of sleep.
The research team used a technique called optogenetics, which uses light to excite brain cells. With this method, researchers can turn neurons on and off. The team found that when the cells were activated, the fruit flies fell asleep. If the cells were turned back off, the flies woke up. There was no between state; manipulation of the neurons always made the flies fall asleep or wake up.
The researchers then turned their attention to the dopaminergic system. It’s well-known that some psychostimulants, including cocaine and caffeine, affect dopamine levels in the brain. Increased levels of dopamine tend to result in enhanced alertness and wakefulness. The research team artificially activated the dopaminergic system of the fruit flies. When it was activated, the flies woke up and stayed awake. If it was shut down, the flies fell back asleep. The dopamine was affecting an ion channel called Sandman, translocating it to the plasma membrane of the cell. This process deactivated the sleep homeostat neurons, forcing the flies to wake up.
These findings provide new insight into how the brain controls sleep functions. By understanding the processes that lead to sleep or wakefulness, we may also be able to develop treatments for sleep disorders.
Diogo Pimentel et al. Operation of a homeostatic sleep switch. Nature (2016).