When you first look at this topic, you may think, what is this problem? Isn't it obvious, without a brain, how to sleep? Of course, there is a brain first, and then there is sleep.
Taichi Q. Itoh, an assistant professor at Kyushu University in Japan, said: "We now have ample evidence that animals must first get sleep before they can get their brains. ”
Taichi Q. Itoh
Professor Ito studies the hydra, a mollusk that has a decentralized neural network but is far removed from the brains of higher animals.
The researchers found that the hydra showed a four-hour active state and a sleep state, rather than repeating every 24 hours, as in the circadian rhythm.
It is said that the hydra is immortal. Source: Kyushu University Tai Chi Ito
Is this four-hour cycle sleep? Scientists need some further experimental means to test.
Exposure of hydra to melatonin, a commonly used sleep aid, was found to increase the amount and frequency of sleep in hydra.
When the eye receives light from the sun, the production of melatonin (Melatonin) in the pineal gland is suppressed, and the hormones produced keep the person awake. When the eye does not receive light, the pineal gland produces melatonin, and the person becomes tired.
The addition of the inhibitory neurotransmitter GABA, another chemical associated with sleep activity in many animals, greatly increased sleep activity.
GaBA-producing neurons
Of course, there are some counterexamples, such as dopamine, which wakes up most animals, but promotes the "sleep" of hydra.
In addition, the researchers also used vibration and temperature changes to interfere with the "sleep" of the hydra, making the hydra "sleep-deprived", and found that the hydra seemed to be tired the next day, slept longer, and even inhibited cell proliferation.
The researchers investigated more closely and found that sleep deprivation caused changes in the expression of 212 genes, including one related to PRKG, a protein associated with sleep regulation in a variety of animals, including mice, fruit flies, and nematodes.
Researchers took turns using different chemicals —Melatonin, the inhibitory neurotransmitter GABA, Dopamine, etc. — to "torture" different levels of animals—hydra, fruit flies, nematodes, sea hares, fish, and people. Professor Ito's research shows that these sleep-regulating components are consistent in the evolutionary tree. Source: Kyushu University Tai Chi Ito
Professor Ito said: "In conclusion, these experiments provide strong evidence that hydra exhibit sleep-related traits at the molecular and genetic levels, which can prove that animals acquired sleep-related mechanisms before the central nervous system evolved, and that many of these mechanisms were protected during brain evolution." ”
So, what do you think?
More information:
Hiroyuki J. Kanaya et al, A sleep-like state in Hydra unravels conserved sleep mechanisms during the evolutionary development of the central nervous system, Science Advances (2020). DOI: 10.1126/sciadv.abb9415
Journal information: Science Advances