Neurobiologists discovered that fruit flies are preprogrammed to take a nap in the middle of the day. The new research examines a “thermometer” circuit for high temperatures.
Temperature influences the duration of human behavior, of eating and activity
levels to sleep-wake cycles. It’s harder to sleep in the summer
and get out of bed slowly on colder mornings.
But the link between sensory neurons and neurons that control this cycle is not fully understood.
Neurobiologists at Northwestern University have found a few clues about what’s…
happens. In a new study recently published in the journal Current
Biology researchers discovered that fruit flies are preprogrammed to take a nap
the middle of the day.
As a follow-up to their 2020 Biology paper that identified a brain thermometer that is active only in cold weather, the new paper explores a similar “thermometer” circuit for high temperatures.
“Changes in temperature have a strong effect on the behavior of both humans and
animals, and signal animals that it is time to adapt to the changing seasons,”
said Marco Gallio, associate professor of neurobiology at Weinberg College
of Arts and Sciences.
“The effect of temperature on sleep can be quite extreme, with some animals deciding to sleep in for an entire season — think a hibernating bear — but the specific brain circuits that mediate the interaction between temperature and sleep centers remain largely unknown.”
Gallio led the research and said fruit flies are a particularly good model to study
big questions like “why do we sleep” and “what does sleep do for the brain”
because they don’t try to upset the instinct in the same way that humans do when we’re trekking through the night, for example. They also enable researchers to
influence of external signals such as light and temperature on cellular pathways.
Cells that last longer.
The paper is the first to identify “absolute heat” receptors in the head of the fly, which
respond to temperatures above about 77 degrees Fahrenheit – the fly’s favorite
temperature. It turns out that the common laboratory fruit fly (Drosophila)
colonized almost the entire planet by forming close bonds with humans.
Not surprisingly, his favorite temperature also matches that of many people.
Exactly as they expected based on the results of their previous paper on cold
temperature, researchers found that brain neurons receive information about
heat is part of the wider system that regulates sleep.
When the warm circuit, which runs parallel to the cold circuit, is active, the target cells that promote midday sleep stay on longer. This results in an increase in midday sleep that keeps flies away from the hottest part of the day.
The study was made possible by a 10-year initiative that completed the first
map of neural connections in an animal (a fly), called the connectome. With the
connectome researchers have access to a computer system that tells them everything
possible brain connections for each of the fly’s ~100,000 brain cells.
However. even with this extremely detailed roadmap, researchers still have to figure out how information in the brain moves from point A to B. This article helps fill that gap.
The different circuits for hot versus cold temperatures make sense for Gallio
because “warm and cold temperatures can have very different effects on
physiology and behavior,” he said.
This separation may also reflect evolutionary processes based on Earth’s heat and cold cycles. For example, based on this work, the possibility can now be explored that brain centers for sleep are targeted directly at humans by a specific sensory circuit.
Next, Gallio’s team hopes to find out the common goals of cold and hot
circuit, to discover how each can affect sleep.
“We identified one neuron that could be a site of integration for the effects of
hot and cold temperatures on sleep and activity in Drosophila,” said Michael
Alpert, the paper’s lead author and a postdoctoral researcher in the Gallio lab.
“This would be the start of interesting follow-up studies.” Gallio added that the team is interested in looking at the long-term effects of temperature on behavior and physiology to understand the impact of global warming, looking at how adaptable species can change.
Gallio added that the team is interested in the long-term effects of
temperature on behavior and physiology to understand the impact of global
warming, looking at how adaptable species will change.
“People can choose to take an afternoon nap on a hot day, and in some parts
of the world this is a cultural norm, but what do you choose and what is?
programmed in you?” said Gallio.
“Of course it’s not cultured in flies, so there could be a very strong underlying biological mechanism that is being overlooked in humans.”
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