Researchers have found that neural signatures in sleeping zebrafish are analogous to those of humans, suggesting that the brain activity evolved at least 450 million years ago, before any creatures crawled out of the ocean.
Scientists have known for more than 100 years that fish enter a sleeplike state, but until now they didn't know if their sleep resembled that of land animals.
The researchers found in the journal Nature that when zebrafish sleep, they can display two states that are similar to those found in mammals, reptiles and birds: slow-wave sleep and paradoxical, or rapid eye movement, sleep. The discovery marks the first time these brain patterns have been recorded in fish.
To study the zebrafish, common aquarium dwellers also known as danios, the researchers built a benchtop fluorescent light-sheet microscope capable of full-fish-body imaging with single-cell resolution. They recorded brain activity while the fish slept in an agar solution that immobilized them. They also observed the heart rate, eye movement and muscle tone of the sleeping fish using a fluorescence-based polysomnography that they developed.
They named the sleep states they observed "slow-bursting sleep," which is analogous to slow-wave sleep, and "propagating-wave sleep," analogous to REM sleep. Though the fish don't move their eyes during REM sleep, the brain and muscle signatures are similar. (Fish also don't close their eyes when they sleep, as they have no eyelids.)
The researchers found another similarity between fish and human sleep. By genetically disrupting the function of melanin-concentrating hormone, a peptide that governs the sleep-wake cycle, and observing neural expressions as the fish slept, the researchers determined that the hormone's signaling regulates the fish's propagating wave sleep the way it regulates REM sleep in mammals.
Other aspects of their sleep state are similar to those of land vertebrates, the senior author said: The fish remain still, their muscles relax, their cardio-respiratory rhythms slow down and they fail to react when they're approached.
"They lose muscle tone, their heartbeat drops, they don't respond to stimuli -- the only real difference is a lack of rapid eye movement during REM sleep," the senior author said, and added, "The rapid movement of the eyes is not a good criterion of this state, and we prefer to call it paradoxical sleep, as the brain looks awake while one is asleep."
While scientists can't say for certain that all animals sleep, it appears to be a universal need among vertebrates and invertebrates. Animals will die if they are deprived of sleep long enough, and people who fail to receive adequate sleep suffer from mental problems such as memory lapses and impaired judgment, along with a higher risk of disorders such as obesity and high blood pressure.
The exact benefits of sleep are still a mystery, however. "It's an essential function," the senior author said, "but we don't know precisely what it does."
The author added that sleep disorders are linked to most neurological disorders such as autism spectrum disorders, Fragile X syndrome, and Alzheimer's and Parkinson's disease. "Sleep disturbances are an aggravating factor of these disorders," the senior author said. It is critical to develop this animal model to study sleep functions at the cellular level, including neuronal connectivity and DNA repair, and in turn understand the pathophysiological consequences of sleep disruptions, the author added.
The discovery means sleep research can be conducted on zebrafish, which are easy to study, in part because they're transparent. They breed quickly, are inexpensive to care for and are just over an inch long. Drug testing requires only the addition of chemicals to their water.
"Because the fish neural signatures are in essence the same as ours, we can use information about them to generate new leads for drug trials," the lead author said and added that mice, often a stand-in for human research, are nocturnal and a less relevant model for our sleep.
"As zebrafish are diurnal like humans, it's perhaps more biologically accurate to compare fish sleep with humans' for some aspects," the author said.
http://med.stanford.edu/news/all-news/2019/07/neural-sleep-patterns-emerged-at-least-450-million-years-ago.html
https://www.nature.com/articles/s41586-019-1336-7
Latest News
Metabolic rewiring promotes…
By newseditor
Posted 18 Apr
A drug to prevent flu-induc…
By newseditor
Posted 18 Apr
New origin of deep brain waves
By newseditor
Posted 17 Apr
Starving cells hijack prote…
By newseditor
Posted 17 Apr
Miniature battery-free epid…
By newseditor
Posted 17 Apr
Other Top Stories
A mere drop of blood makes skin cells line up
Read more
Mannose changes gut microbiome and prevents obesity
Read more
Diabetes may begin more than 20 years before diagnosis
Read more
Intermittent fasting an alternative to insulin for type 2 diabetes…
Read more
Brief beneficial effect of one amino acid in short term lowering gl…
Read more
Protocols
MemPrep, a new technology f…
By newseditor
Posted 08 Apr
A tangible method to assess…
By newseditor
Posted 08 Apr
Stem cell-derived vessels-o…
By newseditor
Posted 06 Apr
Single-cell biclustering fo…
By newseditor
Posted 01 Apr
Modular dual-color BiAD sen…
By newseditor
Posted 31 Mar
Publications
How does the microbiota con…
By newseditor
Posted 18 Apr
The integrated stress respo…
By newseditor
Posted 18 Apr
The immunobiology of herpes…
By newseditor
Posted 17 Apr
Circulating microbiome DNA…
By newseditor
Posted 17 Apr
Spindle oscillations in com…
By newseditor
Posted 17 Apr
Presentations
Hydrogels in Drug Delivery
By newseditor
Posted 12 Apr
Lipids
By newseditor
Posted 31 Dec
Cell biology of carbohydrat…
By newseditor
Posted 29 Nov
RNA interference (RNAi)
By newseditor
Posted 23 Oct
RNA structure and functions
By newseditor
Posted 19 Oct
Posters
A chemical biology/modular…
By newseditor
Posted 22 Aug
Single-molecule covalent ma…
By newseditor
Posted 04 Jul
ASCO-2020-HEALTH SERVICES R…
By newseditor
Posted 23 Mar
ASCO-2020-HEAD AND NECK CANCER
By newseditor
Posted 23 Mar
ASCO-2020-GENITOURINARY CAN…
By newseditor
Posted 23 Mar