Staying awake for too long and thinking straight can be extremely difficult. It's often enough
“We now have strong evidence that animals must have acquired the need to sleep before they acquired brains.”
Taichi K. Ito, Associate Professor, Faculty of Arts and Science, Kyushu University
In research to help understandthe evolutionary origin of sleep in animals, an international team of researchers has shown that tiny aquatic hydras not only show signs of sleep despite the lack of a central nervous system, but also respond to molecules associated with sleep in more advanced animals.
While sleep behavior was recentfound in jellyfish, relatives of hydra, a new study by scientists from Kyushu University in Japan and Ulsan National Institute of Science and Technology in Korea found that certain chemicals that induce drowsiness and sleep had similar effects on Hydra vulgaris species.
"Based on our discoveries andFrom previous reports on jellyfish, we can say that the evolution of sleep is independent of the evolution of the brain. Many questions still remain regarding how sleep originated in animals. Hydras provide an easy-to-handle creature for further study of the detailed mechanisms that induce sleep in brainless animals."
Taichi K. Ito, Associate Professor, Faculty of Arts and Science, Kyushu University
Hydras are only a couple of centimeters long, and they havean extensive network of nerves, but do not have the inherent centralization of the brain. Although sleep is often monitored based on measurements of brain waves, this is not an option for tiny, brainless animals.
Alternatively researchersused a motion-tracking video system to determine when the hydras were in a sleep state characterized by reduced movement that could be disrupted by a flash of light.
Instead of repeating every 24 hoursLike a circadian rhythm, the researchers found that hydras exhibit a four-hour cycle of active and sleep-like states. More importantly, the researchers found multiple similarities associated with sleep regulation at the molecular and genetic level, regardless of the presence of a brain.
Effects on melatonin hydra, widespreadthe hypnotic used moderately increased the amount and frequency of sleep, while the inhibitory neurotransmitter GABA, another chemical associated with sleep activity in many animals, significantly increased sleep activity. On the other hand, dopamine, which induces arousal in many animals, promoted sleep in hydras.
"While some sleep mechanisms appear to have been conserved, others may have switched function during brain evolution."
Taichi K. Ito, Associate Professor, Faculty of Arts and Science, Kyushu University
In addition, researchers could usevibrations and temperature changes to disrupt hydra sleep and cause signs of sleep deprivation, causing hydras to sleep longer the next day and even inhibiting cell proliferation.
On closer inspection, scientistsfound that sleep deprivation leads to changes in the expression of 212 genes, including a gene associated with PRKG, a protein involved in the regulation of sleep in many animals, including mice, fruit flies and hookworms.
"Taken together, these experimentsprovide compelling evidence that animals acquired sleep-related mechanisms before the evolutionary development of the central nervous system, and that many of these mechanisms were retained as the brain developed."
Taichi K. Ito, Associate Professor, Faculty of Arts and Science, Kyushu University
Disruption of other fruit fly genes that,appear to share an evolutionary lineage with sleep-related genes in hydra altered sleep duration, and further investigation of such genes could help identify currently unknown sleep-related genes in animals with brains.
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