The black bears of Alaska spend up to seven months in hibernation every year without ever eating, drinking, urinating or defecating, and when they emerge from their long slumber, it is as if nothing had happened. They are in practically the same physiological condition as when they enter hibernation.
Researchers studying this remarkable feat have found that the bears are able to drop their heart rate to just 14 beats per minute and reduce their metabolism by three-quarters.
Their findings could lead to the development of techniques for inducing hibernation-like states in humans, paving the way for improved treatment of those who are critically ill and helping astronauts survive long missions in deep space.
The hibernation of smaller animals, such as mice and hedgehogs, is well understood, but larger, human-sized animals that hibernate have never been studied before.
DENS
Oivind Toien and colleagues from the Institute of Arctic Biology at the University of Alaska placed captured bears in wooden huts designed to look like dens. The huts were fitted with infrared cameras and the researchers also implanted radio transmitters into the animals to monitor their body temperature, heart rate and muscle activity.
The results of the research were published on Thursday in Science and presented at the annual meeting of the American Association for the Advancement of Science.
“We wanted to follow metabolism to see whether or not the animals were regulating body temperature,” said Craig Heller of Stanford University, who took part in the study.
“We wanted to study EEG [electroencephalogram] in order to reveal their sleep states and circadian rhythms,” he said.
CYCLES
The scientists monitored the bears during five months of hibernation and watched as their body temperatures fluctuated between 30oC and 36oC in cycles lasting two to seven days.
These fluctuations have never been seen before in hibernating animals.
At the end of the hibernation season, the bears’ metabolism remained suppressed for up to three weeks after they emerged from sleep.
“That indicates there’s some biochemical mechanism that suppresses metabolism and that could be a very interesting discovery,” Heller said.
The findings suggest how hibernation could be induced in people.
“If our research could help by showing how to reduce metabolic rates and oxygen demands in human tissues, one could possibly save people,” Toien said.
TURN ONS
“We simply need to learn how to turn things on and off to induce states that take advantage of the different levels of hibernation,” he said.
Heller also pointed to lessons the study could have for deep-space exploration.
“There has always been a thought that, if there is ever long-distance space travel, it would be good to be able to put people into a state of lower metabolism or suspended animation — that’s almost science fiction, but you can see the rationale,” Heller said.
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