Fruit fly study finds long-term impact of sleep deprivation

Print Friendly
Fruit fly study finds long-term impact of sleep deprivation
golden fly with red eyes and black striped abdomen
Fruit fly, Drosophila melanogaster. Shutterstock

Most of us know more about sleeping babies than snoozin’ fruitflies, but most young animals need buckets of sleep. Today, a study published in Science offers a comprehensive picture of why newborns sleep so much, and what difference it makes — at least to a fruit fly.

The goal “was to show that sleep early in development is required for normal structural growth of the brain,” says first author Matthew Kayser, a physician in the department of psychiatry at the University of Pennsylvania.

The basic plan was to reduce sleep among fruit flies that had just emerged from the pupal stage, and then look at their brains and behavior eight or nine days later. (Technically, fruit flies become adults immediately after the pupal stage, so we’ll call the day 1 flies “youngsters” and the day 8, 9, or 10 flies “oldsters.”)

Before starting, the researchers knew that

tiny fruit fly Dopamine, a common neurotransmitter, causes waking in the fruit fly

tiny fruit fly The brain’s dorsal fan-shaped body promotes sleep in the fruit fly

tiny fruit fly Fruit flies that were kept awake just after emerging from the pupal stage failed to mate normally as mature adults

ENLARGE
Dark grey baby gorilla sleeps face down, hands gripping mother's fur (head towards mother's rear) on it's mother's back as mother walks on all fours.
Baby gorilla snoozes on mom. Why do babies sleep so much?

If there’s one thing that concerns evolution, it’s mating, says Kayser, a specialist in the neurobiology of sleep. This abundance of sleep in young animals is found “across the board, in humans, other mammals, even fruit flies. Things that are conserved like that tend to be important.”

But exactly what mechanism causes extended dormancy among young flies?

First, Kayser and senior author Amita Sehgal, of the Howard Hughes Medical Institute and the Perelman School of Medicine at the University of Pennsylvania, measured sleep. They found that the youngsters slept almost 17 hours a day, versus about 12 for oldsters. Sleep was also “deeper”: only about 25 percent of the young awoke after 10 seconds of light, versus 65 percent of oldsters.

Those drowsy, young flies also had 30 percent less dopamine than the older flies.

ENLARGE
a comparison showing that a fan-shape body has lighter green than that of the older one
Green indicates activity of dopamine neurons in the sleep-promoting dorsal fan-shaped body (outlined). Because dopamine inhibits the fan-shaped body, older flies (with high dopamine) sleep less than younger flies.
Credit: Matthew Kayser

Better than coffee?

When Sehgal and Kayser raised dopamine levels in the young flies, their increased wakefulness demonstrated that the normal condition — increased sleep and resistance to waking when young — results from a low dopamine level.

Moving on, the researchers found that the normal low-dopamine condition in the young flies was due to decreased dopamine production among specific neurons that connect to a sleep-promoting structure called the dorsal fan-shaped body. “If you want to disrupt early sleep, the best way to do it is by activating these dopamine neurons,” to slow the sleep-promoter, Sehgal told us. “The animal begins to resemble a mature adult,” and spends more time awake (maybe finishing its tax returns or pressing buttons on a phone?).

In other words, more dopamine translates to less sleep.

Looking further, the researchers found that a structure in the brain’s olfactory (smell) system was stunted in the sleep-deprived oldsters. Normally, this structure grows for a while during adulthood, “But sleep loss is stunting the growth of this structure, and so we are saying that sleep is required for these actively growing regions,” Sehgal says.

It turns out that the structure in question detects pheromones — chemicals that flies use to communicate about mating and other necessities.

Mating matters

To recap, dopamine inhibits the sleep-promoting fan-shaped body, and excess dopamine at day 1 reduces sleep, which interferes with growth in a part of the brain linked to mating. Sehgal and Kayser already knew that young flies that got less sleep caused a significant reduction in courting and mating behavior. And the same result appeared in their dopamine-rich, sleep-deprived flies.

“Honey, I’m too tired tonight,” say the flies on the right (or so we guess). Deprived of sleep as young adults, their brains — and behavior — are abnormal.
Credit: Matthew Kayser and Amita Sehgal

In science, every good answer raises a question, and Sehgal mentions these:

tiny fruit fly What is the ultimate reason that dopamine is less abundant at day one?

tiny fruit fly How does sleep assist the growth of some brain structures?

tiny fruit fly What other parts of the brain are harmed by a lack of sleep in early life?

Ultimately, Sehgal says, research on early sleep abnormalities could shed light on problems like sudden infant death syndrome. “There are data showing that SIDS is somehow connected to sleep. We are being very speculative, but if sleep is important for circuits developing in the brain, deprivation of sleep could be quite harmful.”

– David J. Tenenbaum

1 2 3 4 5 6

Terry Devitt, editor; S.V. Medaris, designer/illustrator; Yilang Peng, project assistant; David J. Tenenbaum, feature writer; Amy Toburen, content development executive

Bibliography

  1. A Critical Period of Sleep for Development of Courtship Circuitry and Behavior in Drosophila, by Matthew Kayser et al, Science 18 April 2014.
  2. Animal Sleep Game
  3. Why Do Humans and Many Other Animals Sleep?
  4. Sleep Deprivation Amps Up the Brain
  5. How Slight Sleep Deprivation Could Add Extra Pounds
  6. Sleep Deprived? Mind your dopamine