Axios Science – July 11, 2019

Most animals sleep, but scientists still do not fully understand why, the biological factors that regulate sleep cycles and how evolved.

• A new study in Nature on a zebrafish finds that the sleep of today 's men may have evolved in vertebrates over 430 million years ago.

Why it's important: Scientists hope that a better understanding of how zebrafish sleep, up to the cellular level, could pave the way for new treatments for sleep disorders that affect 50 to 70 million people. Americans but are often undiagnosed. It could also improve their understanding of the role of sleep in memory and our physical health.

What did they do: Zebrafish do not have neocortex – part of the mammalian brain involved in higher order functions such as sleep and sleep studies target – scientists from the University of Stanford and institutions in Japan and France have had to find a workaround.

• They have developed an imaging platform allowing them to visualize the proxies for brain and muscle activity via fluorescence, as well as heart rate and eye movements.
• They used the two-week-old zebrafish because they are transparent, and therefore ideal for fluorescent imaging techniques.
• They also conducted other experiments to determine the effects of particular compounds on zebrafish sleep and waking cycles.

What they found: Ependymal cells – present in humans and zebrafish, and known to play a role in the brain and spinal cord – are among the first to be activated when the fish go to sleep.

• The researchers also found that human hypnotics – compounds found in sleeping pills and anesthetics – can also induce sleep phases in fish, similar to humans.
• And as in humanity, the chemicals released by zebrafish brain neurons regulate the creature's muscles and sleep.

What's up: Scientists have observed invertebrates (octopus, insects) and vertebrates (fish, amphibians, birds, mammals) sleeping, but the physiological signatures of sleep, such as rapid eye movements, has only been observed in mammals, birds and reptiles, the co-author of the study, Philippe Mourrain of Stanford University, told Axios.

What they say: "You can not just say that sleeping, it's sleepy," Jerry Siegel, a sleep scientist at UCLA, who was not involved in the study, told National Geographic. He warned that the links between sleep in young zebrafish and sleep in humans are less simple than suggested by the study. For example, he said, many mammals are completely lacking REM sleep and some sleep 20 hours a day, while others need 6 to 8 hours or less.

The senior author of the study, Louis C. Leung of Stanford, told Axios:

"I encourage everyone to cherish what it took hundreds of millions of years to create and hope that there will soon be a change in public narrative. regarding the importance of sleep – we should be proud not to be embarrassed to sleep enough. "

And after: Develop animal models that examine sleep functions at the cellular level, such as this study, could lead to treatments for sleep disorders related to psychiatric disorders, Parkinson's disease and Alzheimer's disease.