Our brain needs daily rest to think clearly and function properly. If we stay awake too long, any task becomes extremely complicated, right? But at what point did the animals begin to need to sleep? Is it a prerequisite to have the brain for it?
The quick answer is: no. You can sleep without a brain . This is the conclusion of a study published in the journal Science Advances and which exposes that some small invertebrates that do not have a brain, called Hydra vulgaris, a tiny creature similar to a jellyfish (1-3 cm long) but a similar state to sleep. And without counting on the central nervous system.
The evolutionary origin of sleep in animals
The study showed that, unlike many animals, whose biological clock revolves around a circadian rhythm of approximately 24 hours, Hydra follows a 4-hour sleep-wake cycle.
“We now have strong evidence that animals must have acquired the need to sleep before acquiring a brain,” says Taichi Q. Itoh, assistant professor at Kyushu University College of Arts and Sciences and leader of the study.
Since sleep, something almost universal in the animal kingdom, is generally monitored via brain waves, but Hydra does not have a brain, the researchers used videos to track whether the animal was in a sleep-like state based on the amount of movement it had. performed. They found that hydras had cycles of active and sleep states lasting about four hours each. They also measured gene activity in response to disruptions in the sleep state with vibrations or changes in temperature that gave clear signs of sleep deprivation (such as needing longer hours of sleep or showing reduced cell growth).
Finally, they identified that their sleep was controlled by 212 genes , including a gene that produces ‘PRKG1’, a key protein that regulates sleep in all animals, from flies and nematode worms to mice and other mammals.
Jellyfish, a relative of hydras that also lack a brain, have also shown similar behavior to sleep, but this finding shows that hydras not only sleep, but also respond to the same molecules that regulate sleep in humans and other advanced animals .
“Based on our findings and previous reports on jellyfish, we can say that sleep evolution is independent of brain evolution ,” Itoh said.
The scientists also exposed hydras to chemicals involved in regulating sleep in people, including melatonin and the neurotransmitter, or brain chemical called GABA . Exposing them to these two chemicals increased sleep activity in the hydras.
These reactions give researchers more clues about how sleep may have evolved in the animal kingdom, both before and after living organisms developed a brain. What is unclear is whether the disorganized network of nerves within Hydra vulgaris is playing a key role or not , so further experiments are needed to answer the many unanswered questions we still have about the brain.
Referencia: A sleep-like state in Hydra unravels conserved sleep mechanisms during the evolutionary development of the central nervous system. Hiroyuki J. Kanaya, Sungeon Park, Ji-hyung Kim, Junko Kusumi, Sofian Krenenou, Etsuko Sawatari, Aya Sato, Jongbin Lee, Hyunwoo Bang, Yoshitaka Kobayakawa, Chunghun Lim, and Taichi Q. Itoh. Science Advances (2020).DOI:https://doi.org/10.1126/sciadv.abb9415
