Sleep as a strategy to cope with energy shortage
IMP scientists demonstrate that brain activities are resistant to severe energy deprivation and that sleep could be a major strategy to cope with this type of stress.
The processing of information by brains is a basis of behaviour and crucial for survival, but it also requires a lot of energy. Brains have evolved to work in an energy-efficient manner, but how they do so is incompletely understood. Findings by scientists from the lab of Manuel Zimmer at the Research Institute of Molecular Pathology (IMP) published in the journal Cell Reports suggest that sleep might play a crucial role in saving energy.
The scientists used the nematode worm Caenorhabditis elegans as a model. Its nervous system comprises only 302 cells, making it comparably easy to study. Susanne Skora, then a PhD student in Manuel Zimmer’s lab, discovered that depriving the animals of food initially enhances their arousal: they become more attentive to their environment and vigorously search for food. However, when deprived of food for longer periods, worms suppress their food search behaviours and frequently fall asleep.
Skora next used functional brain-wide imaging to assess the changes in brain activity that occur upon severe starvation. Instead of finding the brain in some sort of energy-saving mode, the scientists were surprised to see that brain activity in awake animals is to a large extent unaffected by starvation. Contrary to awake periods, brain activity is largely silenced during the frequent starvation-induced sleep episodes. These findings suggest that animals maintain most brain functions despite their potentially high metabolic costs and that energy might be saved by the introduction of sleep episodes.
Zimmer and his team were curious how the brain regulates this strategy. They found that a well-known metabolic hormone, insulin, acts on neurons to prevent falling asleep as long as animals still have sufficient energy reserves. However, upon prolonged food deprivation, insulin signalling progressively declines, which leads the animals to rest and sleep.
Sleep is a universal property of all animals, but scientists still debate its major functions. The findings made by Zimmer and his team support the hypothesis that one function of sleep is the conservation of energy resources.
More about Manuel Zimmer’s research: https://www.imp.ac.at/groups/manuel-zimmer/
About the VBC PhD Programme
Much of the work underlying this publication was done by doctoral students at the IMP, enrolled in the Vienna BioCenter PhD Programme. Find out more about training opportunities for young scientists: www.imp.ac.at/career/phd-master
Susanne Skora, Fanny Mende, Manuel Zimmer (2018). “Energy scarcity promotes a brain-wide sleep state modulated by insulin signaling in C. elegans”. Cell Reports.
About the IMP
The Research Institute of Molecular Pathology (IMP) in Vienna pursues world-class research in basic molecular biology. It is located at the Vienna BioCenter and largely sponsored by Boehringer Ingelheim. With over 200 scientists from 40 countries, the IMP is committed to scientific discovery of fundamental molecular and cellular mechanisms underlying complex biological phenomena. www.imp.ac.at
About the Vienna BioCenter
Vienna BioCenter (VBC) is a leading life sciences hub in Europe, offering an extraordinary combination of research, business and education in a single location. About 1,700 employees, 86 research groups, 18 biotech companies, 1,300 students and scientists from 70 nations create a highly dynamic and stimulating environment. www.viennabiocenter.org
Differential interference contrast (DIC) images of two C. elegans worms. The top one is in a fed state, the bottom one has been starved, which led to fat loss and the accumulation of unlaid eggs and developing embryos. The work by Skora et al. suggests that low insulin levels in starved worms cause a propensity to sleep that aids the saving of energy.
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