The mechanisms that control drowsiness and other hypothermic states, in which the body temperature falls below 37 degrees Celsius, are largely unknown to science.
We know that a wide variety of animals can go into hibernation. Their metabolism, heart rate and respiration are reduced to a minimum, allowing them to withstand harsh environmental conditions such as cold winters or droughts. Bears are the most popular performing this activity (also bats or squirrels), but now a team of scientists from the University of Tsukuba (Japan) and Harvard Medical School (USA) has discovered how to induce a similar state in mice.
Why do some animals hibernate and others don’t?
The researchers found a neural circuit in the hypothalamus of mice that controls torpor, a hibernation-like state similar to suspended animation we know from science fiction movies and novels (it’s a very common trope in space travel). Mice do not hibernate, but enter a state known as daily torpor, lasting only a few hours, to conserve energy when food is scarce. By stimulating these neurons, the quiescence-inducing neurons (Q neurons), the researchers were able to induce lethargy in mice for days.
The hypothalamic neuronal circuitry in rodents induced “a long-lasting hypothermic and hypometabolic state similar to hibernation,” the authors wrote. During this state of Q neuron-induced hypothermia and hypometabolism (QIH), they noted that “although body temperature and oxygen consumption levels remained very low, the ability to regulate metabolism remained functional, as in hibernation.” . They added that “there was no obvious tissue and organ damage or behavioral abnormalities after recovery from this state.”
This natural state of sleep was also triggered in rats, which generally do not hibernate or go into a state of torpor, according to Japanese scientists. Studying sleepiness in mice helps us understand how this fascinating feature of heat prevents body temperature from dropping dramatically . “
It might be possible to induce synthetic hibernation in humans if we happen to have the same set of brain cells as the mice and rats involved in this study.
Being able to put someone in suspended animation could improve recovery rates from surgery or illness, according to the team. It could also make interplanetary travel safer.
“Imagination runs wild when we think of the potential for hibernation-like states in humans. Could we really extend lifespan? Is this the way to send people to Mars? ” Study co-lead author Sinisa Hrvatin commented that “to answer these questions, we must first study the fundamental biology of torpor and hibernation in animals. We and others are doing this; it is not science fiction.”
This work, published in Nature , paves the way toward understanding how these conditions are initiated and controlled. Ultimately, it could also help find methods to induce hypothermic states in humans that will prove useful in medical settings. And more speculatively, such methods could one day approximate the suspended animation technology so well known to fans in the ci-fi world.
Be that as it may, small mammals have very different temperature regulation systems than large mammals, so it is not clear whether these neurons will have the same effect. Researchers will continue to study this process to better understand the long-term effects, as well as the role of other neural circuits involved in this process.
Referencia: Sinisa Hrvatin, Senmiao Sun, Oren F. Wilcox, Hanqi Yao, Aurora J. Lavin-Peter, Marcelo Cicconet, Elena G. Assad, Michaela E. Palmer, Sage Aronson, Alexander S. Banks, Eric C. Griffith, Michael E. Greenberg. Neurons that regulate mouse torpor. Nature, 2020; DOI: 10.1038/s41586-020-2387-5
