Editor’s note: This article originally appeared in the Dec. 27, 2017, edition of the New York Times with the headline “Temperamental: Squirrels That Carry Internal Thermostats.” It is reprinted here with permission
Most rodents are just rodents. And the ones with exceptional abilities are usually cartoon rats or mice.
But here in the real world of flesh, bones, brains and nerves that we mammals use each second to survive, some woodland rodents really do have a superpower that helps them tolerate cold and endure harsh winters.
In grasslands from central Canada to Texas, a species known as thirteen-lined ground squirrels can adjust their body temperature to match the air around them. This is especially important during hibernation: They don’t have to fatten up like bears or find warm hide-outs like conventional mice and rats. They slumber, surviving in bodies just above freezing. Another species, the Syrian hamster, does it too. “They combine warm and cold blooded animals in one,” said Elena Gracheva, a neurophysiologist at Yale University.
This uncanny ability to withstand prolonged cold (and even hypothermia) results in part from an adaptation these rodents have developed in molecules they share with other mammals, including us, Dr. Gracheva and her colleagues found in a study published in December 2017 in the journal Cell Reports. Unique properties of TRPM8, a cold-sensing protein found in their peripheral nervous systems, shields these rodents from harsh weather. It’s really important because if they’re too cold, they can’t hibernate — just like if you’re too cold, you might have trouble sleeping.
The new research brings scientists closer to understanding enigmas of hibernation and solving a mystery of how this molecular sensor works. The work also may lead to therapies for allodynia, a nerve condition that causes some people to misperceive something normally not-so-cold as painful.
TRPM8 is an ion channel located on some neurons in skin covering the body and face. When exposed to cold air or certain chemicals, like menthol, the pores open, allowing a flood of ions into the cell like cool air through a window. This sends a signal that says something like “hey, it’s cold” to the central nervous system. Humans and other animals use the system to detect cold and, along with other organs, to feel a range of temperatures.
But something is different in the TRPM8 of thirteen-lined ground squirrels and Syrian hamsters (also called Teddy bear hamsters), so the researchers compared their behavior, neurons and proteins with that of standard lab mice and rats.
In one test involving surfaces of varying temperatures, they found that the squirrels and hamsters (to a lesser extent) didn’t seem to notice a temperature gradient that for us might be like the difference between jacket-and-jeans or tank-top-and-shorts weather. The mice were very aware of these temperature differences.
After additional study of extracted TRPM8 proteins, the team found a set of amino acids inside the channel that were the source of the ground squirrel’s seeming imperviousness to cold down to a certain temperature.
If she swapped some of my TRPM8’s amino acids with those of a thirteen-lined ground squirrel, would walking around New York City in winter feel less miserable? Would I have a superpower?
While TRPM8 explains some cold tolerance, it does not fully explain how I in New York or a ground squirrel in, say, Michigan would sense temperatures just above or below freezing. And although it’s a cold detector, it’s not clear what the brain and the rest of the body does with the signal. And while TRPM8 plays a role in the squirrel’s hibernation, it doesn’t trigger it.
“Changing its ability to sense cold, for example, TRPM8, is an important part of the puzzle but not the only one,” said Slav Bagriantsev, a neurophysiologist at Yale University who shares a lab with Dr. Gracheva and a co-author of the study. Lowered metabolism, heart rate and breathing also aid in survival during hibernation.
So maybe becoming a superhuman who doesn’t hate winter so much isn’t a reason to care about TRPM8. But it’s a nice reminder that nature’s diversity produces some real superpowers.
“It’s a fantastic time in science to look outside the mouse book,” said Dr. Gracheva. “You can learn a lot about our human biology, and biology in general, by looking at animals with sensory diversification.”
© 2017, The New York Times.