Fruit flies yield clues to a good night's sleep

New research provides clues to falling fast asleep -- or lying wide awake. While studying fruit flies, researchers observed that the brain neurons adopt the flies to stay awake during dangerous situations despite tiredness and help them in falling asleep after a hectic day. This research is published in PLOS Biology. It can help in improving sleep quality and treating insomnia among people.

"If you're sick or sleep deprived, or you've just learned something new, you sleep more," said co-corresponding author Paul Shaw, PhD, a professor of neuroscience at Washington University. "But if something dangerous is happening, your brain says, 'No, no, no, no. It's not time to go to sleep. I don't care how tired you are.' The neurons that regulate sleep can tell the difference between sleep when it's safe and sleep when it's dangerous."

The sleeping habits of fruit flies and humans are almost similar. As normal humans, fruit flies too stay active during the day time, sleep at night, and take a nap in the afternoon. A most interesting fact is that caffeine keeps them awake, and the drugs used by humans for sleep showed results on flies too.

Talking about the difference, the brain of a fruit fly is a million times smaller than that of a human. Thus, due to the small size, researchers can study the role of each neuron.

 The researchers focused on 24 brain neurons that control the sleep cycle of a fly. These neurons receive and respond to sleep signals sent by other neurons via chemical messengers known as neurotransmitters.

The researchers examined the signals that affect the sleep cycle and how those 24 neurons respond to the neurotransmitters. The signals include Dopamine, which promotes wakefulness; Glutamate, which promotes sleep; and Allatostatin A, which also promotes wakefulness. Allatostatin A was previously known to play a role in feeding behaviors, but now researchers have discovered that it also plays a role in regulating sleep.

As normal human behavior, we tend to sleep more after a hectic challenging day. This is the same case with flies. Researchers revealed that living in a crowded environment trigger molecular changes in the sleep neurons of flies. This makes them less reactive to dopamine, thus increasing sleep.

 During the study, researchers alarmed the flies by periodically shaking the vials. Vials are where the flies live during their sleeping hours. By this, the flies’ brains produced allatostatin A and glutamate. These two opposite sleep signals kept the flies awake. This help flies to even stay awake despite tiredness to deal with dangerous situations.

"A lot of people don't sleep well, and we really don't know why," Shaw said. "Our data suggests that there is a genetic predisposition to how neurological signals are interpreted by sleep centers in the brain. If the system goes astray, then you get these conflicting signals: You're tired, but you can't fall asleep. By understanding how these conflicting signals can arise, we can begin to think about how we might design therapeutics for people."

The researchers also examined the sleep changes to variations in dietary habits. They normally eat through the complete day, but for the observations researchers allowed flies to access food between 8 a.m. and 5 p.m. After a week, the flies' sleep neurons were more sensitive to dopamine, and the sensitivity persisted for days after returning to a normal feeding schedule. The flies slept less, but they didn’t show any sort of tiredness. This showed that the quality of sleep has improved among them.

"Time-restricted eating is a hot topic right now," Shaw said. "The claim is that confining your food intake to certain hours of the day will help you sleep better and maintain a healthy weight. The evidence that this works in people is mixed. But in flies, our data suggests sleep quality improves with time-restricted feeding. It's possible that there's an intersection between time-restricted feeding and sleep regulation that we can take advantage of to help people sleep better."