This super-cooled squirrel could revolutionise emergency care - BBC

In August, as summer draws to a close and the days shorten, a female Arctic ground squirrel knows it's time to fatten up. The small, copper-hued rodent scouts the tundra for whatever food she can find – grasses, sedges, and leaves – until she retreats to her burrow to sink into a deep wintry slumber. About a metre underground, her body winds down into slow motion. At just a few breaths and heartbeats per minute, it would be easy to mistake her for dead.

As the ground above her freezes solid, reaching temperatures of -20C (-4F), her body temperature plummets. Astonishingly, her brain cools to 0C (32F), her abdomen to -2C (28F) and her hind limbs even down to -2.9C (27F) – colder than any other mammal has been recorded alive. For eight months she lies here without food or water, rousing only occasionally, until the ground warms and she returns to life aboveground.

Like many mammals of northern climates, Arctic ground squirrels survive the harsh winters of Canada, Alaska and Siberia by hibernating, but they're somewhat unusual in the sheer length of time they spend in this state and unique in that they survive at such cold body temperatures.

These extreme features have made Arctic ground squirrels, alongside some close relatives, a popular study subject for scientists striving to better understand what makes hibernation biologically possible – not just out of scientific curiosity, but also in the hopes of someday applying this to humans.

Being able to slow down human metabolism could help doctors buy more time in treating severe conditions like heart attacks, strokes, and traumatic brain injuries, and induce beneficial cooling to protect vital organs. And, in the distant future, this research might even pave the way to putting astronauts into states of suspended animation to help them weather long-distance space flights.

This research is young, but it's already showing how studying the animal kingdom's extreme survivors could help unlock new strategies to boost human health. "Their physiology is just so different," says physiological ecologist Cory Williams of Colorado State University. "At the same time, you can see [how] if you could harness this attribute and apply it to humans, there could be real practical function."

Scientists at the University of Alaska Fairbanks have been studying Arctic ground squirrels for more than 50 years. The rodents seem to have an internal clock which – alongside the changing length of daylight – tells them when it's time to hibernate; for females this happens around August while males start a few months later.

Staff then transfer the squirrels from their enclosures into a dark refrigerated room that mimics the conditions inside the rodents' natural hibernation burrows. The animals lie curled up inside cotton or wood shavings inside plastic cages. For certain studies, staff cuddle the animals in the beginning to get them used to being handled so they don't stir when scientists take blood and other measurements, says hibernation scientist Sarah Rice of the University of Alaska Fairbanks. Their bodies are so cold, and their breathing and heartbeat so slow, she says, that "sometimes it's hard to tell if they're alive or not".

Rice's colleagues, including hibernation scientist Kelly Drew, have been investigating what exactly triggers the slowdown in the animals' metabolism that allows their body temperature to drop so low.

Doctors have often used ice or specific medications to cool down certain patients who have had a heart attack or stroke to help protect their vital organs like the brain from the deprivation of oxygen that occurs during these conditions. That strategy doesn't always work and it can be challenging, because the body eventually starts to fight against the cooling and tries to warm itself by shivering.

But if scientists could identify a way of winding down patients' metabolism – which would then naturally allow their body to cool – that might prove more effective, "because the body doesn't fight it", Drew says.

Slowing down metabolism could help to preserve organs destined for transplantation for longer time periods outside the body. It could also help to protect cancer patients against the harmful effects of radiation, which causes dangerous byproducts under normal metabolism, says neurophysiologist Domenico Tupone of Oregon Health and Science University and Italy's University of Bologna.