Do animals feel cold during hibernation? The question seems simple, but for a long time scientists have not understood how bears, bats, snakes, and other animals survive the winter without freezing to death.
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According to a new study, hibernating animals don’t feel winter cold the way we do. «If you expose mouse or human neurons to cold, they start to fire ... like crazy,» says senior author of the study Elena Gracheva, a neurophysiologist at Yale University School of Medicine (the US). But when Gracheva and her colleagues exposed hibernating animals like the 13-lined ground squirrel and the Syrian hamster to the cold, they noticed very low activity in the TRPM8 pathway, a region of the central nervous system that processes information about the cold.
In another laboratory experiment, the scientists gave ground squirrels, hamsters, and mice two platforms to choose from — one with a temperature of 30 degrees Celsius and another with a temperature ranging from +30 to 0 degrees Celsius.
Although hibernating animals preferred the warm platform, they also used the cold one, apparently without feeling the temperature change.
The mice reacted differently to the cold platform. «They touch it with one paw and say, ‘Uh-uh, I don’t want to go there. This is too cold for me’,» Gracheva says. Having touched the cold platform once, the mice never touched it again.
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So, what is the reason for the differences in the behavior of mice, ground squirrels, and hamsters?
Initially Gracheva and her colleagues hypothesized that hibernating animals have fewer cold- sensing cells in the nervous system. But after dissecting several animals’ spines, the team found that ground squirrels and hamsters had about the same number of these cells — but in the first case, they were less sensitive to the cold. To survive the winter or lack of food, animals go through a number of physiological changes, such as reducing their body temperature, heart rate, and breathing rate. Therefore, it is not surprising that hibernating animals have developed techniques within theit central nervous system that help their bodies cope with the cold.
According to Brian Barnes, director of the Institute of Arctic Biology at the University of Alaska-Fairbanks, the loss of sensitivity described in the new study is interesting for another reason: sensing cold is one of the ways helping animals realize that it is time for hibernation.
Gracheva hopes to reveal even more hibernation secrets during her next project to transplant the genes responsible for cold tolerance from squirrels and hamsters into mice.