Do animals freeze during hibernation? The question seems simple, but scientists have long struggled to understand how bears, bats, snakes, and other animals survive the winter without freezing to death.
According to a new study, hibernating animals do not experience winter cold the way we do. "If you put the neurons of a mouse or a human in the cold, they start working... like crazy," says the senior author of the study, Elena Gracheva, a neurophysiologist at Yale School of Medicine (USA).
But when Gracheva and her colleagues placed some hibernating animals, such as the thirteen-lined ground squirrel and the Syrian hamster, in the cold, they noticed very low activity in the TRPM8 channel, a part of the central nervous system that processes information about cold.
In another laboratory experiment, the scientists gave the squirrels, hamsters, and mice two platforms to choose from—one at a temperature of 30 degrees Celsius and the other with a temperature ranging from +30 to 0 degrees Celsius.
Although the hibernating animals preferred the warm platform, they also used the cold one, apparently not sensing the temperature change. Mice reacted differently to the cold platform. "They touched it with one paw, as if saying: oh, I don’t want to go there, it’s too cold," Gracheva recounts. After touching the cold platform once, the mice did not touch it again.
So, what is the reason for the differences in behavior between mice, chipmunks, and hamsters?
Initially, Gracheva and her colleagues hypothesized that hibernating animals have fewer cold-sensitive cells in their nervous system. But after dissecting several animal spines, the team found that squirrels and hamsters had roughly the same number of these cells—just that in the former case, the sensitivity to cold was lower. To survive winter or food shortages, animals undergo a series of physiological changes, such as a decrease in body temperature, heart rate, and breathing rate. Thus, it is not surprising that hibernating animals have developed mechanisms within the 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 in Fairbanks, the loss of sensitivity described in the study is interesting for another reason: the sensation of cold is one way that animals understand it is time to hibernate.
