State of hibernation induced in mice — are humans next?

Why do some animals hibernate while others do not? Do all animals have the potential to hibernate, even if they never do so in nature? Japanese researchers sought to answer these questions by finding specific cells in the mouse brain that can trigger a hibernation-like state when activated. Their study has been published in the journal Nature.

Animals usually enter hibernation when food becomes scarce in the winter. Their metabolism slows down and their body temperature drops to a new set-point. This is like lowering the temperature on your thermostat in the winter — it reduces the amount of energy needed to maintain the body. Along with a slower metabolism and a new set-point comes slower heart rate, weaker breathing and less brain activity. Importantly, when animals come out of hibernation, their body and organs are healthy, even if they have lost a little weight.

Researchers led by Takeshi Sakurai at the University of Tsukuba and Genshiro Sunagawa at RIKEN showed that activating a specific type of cell in the mouse brain — dubbed Q neurons — caused them to enter a hibernation-like state for several days. This is despite the fact that mice would not otherwise hibernate, though they do exhibit a similar temporary hypometabolic state called torpor.

“The mice exhibited distinctive qualities that met the criteria for hibernation,” Sakurai said. “In particular, the body temperature set-point lowered from about 96.8°F [36°C] to about 81°F [27°C], and the body functioned normally to maintain a lower body temperature around 22°C, even when the surrounding ambient temperature was dramatically reduced.” The mice also showed all the signs of a reduced metabolism that are common during hibernation, including reduced heart rate, oxygen consumption and respiration.

Being able to send mice into a hibernation-like state for days simply by artificially exciting Q neurons was somewhat unexpected. These neurons could be activated synthetically with chemicals or light, and no adverse effects on mouse behaviour or damage to tissues and organs were observed.

“Even more surprising is that we were able to induce a similar hypometabolic state in rats — a species that neither hibernates nor has daily torpor,” said first author Tohru Takahashi. This suggests that artificial induction of a hibernation-like state could occur in a broad range of mammals, even in non-hibernating species such as humans.

“There are medical reasons for wanting to place people in suspended animation, such as during emergency transport or critically ill conditions as in severe pneumonia, when the demand for oxygen cannot meet the supply,” Sunagawa said.

Suspended animation would also be useful for astronauts crossing the vastness of space, with ‘hibernation chambers’ in sci-fi movies inducing a state of unconsciousness that could cut down on the required amount of food and oxygen; prevent serious side effects from low gravity, such as muscle wasting; and potentially minimise psychological challenges in space.

“In the future, we may put humans in a hibernation-like state for missions to Mars and beyond,” Sakurai said.