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Keeping Their Cool

How strange rodents have adapted to their steamy desert home

March 6, 2017
By Andrew Klein

ESSENTIAL QUESTION: Why might it benefit an animal to not feel pain from heat?

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IDENTITY CRISIS: Naked mole-rats aren’t moles, or rats. They’re more closely related to guinea pigs.

This weird-looking creature is a naked mole-rat . . . and it’s probably not hard to see how it got its name. These nearly hairless rodents live together in burrows beneath the deserts of east Africa. It gets hot and uncomfortable inside these cramped underground holes. But the naked mole-rats have a way to beat the heat: They’re nearly immune to pain caused by high temperatures.

For most animals, “Pain is primarily protective,” says Gary Lewin, a neuroscientist at the Max Delbrück Center for Molecular Medicine in Berlin, Germany. The sensation of pain is like an alarm warning organisms to stop doing something harmful—like touching a hot stove. Without this signal, they could badly injure themselves. About 20 million years ago, naked mole-rats branched off from other mole-rat species and lost this pain response—making life a little more manageable in their sweltering burrows.

This weird-looking creature is a naked mole-rat. It’s probably not hard to see how it got its name. These rodents are almost hairless. They live together in burrows under the deserts of east Africa. It gets hot and uncomfortable in these cramped underground holes. But the naked mole-rats have a way to beat the heat. They’re nearly immune to pain caused by high temperatures.

For most animals, “pain is primarily protective,” says Gary Lewin. He’s a neuroscientist at the Max Delbrück Center for Molecular Medicine in Berlin, Germany. The feeling of pain is like an alarm. It warns creatures to stop doing something harmful—like touching a hot stove. Without this signal, they could badly hurt themselves. About 20 million years ago, naked mole-rats branched off from other mole-rat species. They lost this protective pain response. That makes life a little easier in their sweltering burrows.

FEELING LESS PAIN

Lewin recently led a team of scientists in learning more about this unusual adaptation. The researchers grew nerve cells from naked mole-rats and mice in their lab. Then they exposed the cells to nerve growth factor (NGF)—a molecule that triggers nerves to signal to the brain that they are sensing pain (see Pain Signals). It took about 10 times the amount of this chemical to cause the same pain signals in a naked mole-rat’s cells versus those of mice.

Lewin wanted to learn more about this unusual adaptation. So he led a team of scientists in a recent study. The researchers grew nerve cells from naked mole-rats and mice in their lab. Then they exposed the cells to nerve growth factor (NGF). This molecule triggers nerves to signal the brain that they sense pain (see Pain Signals). The researchers noted how much of this chemical was needed to cause pain signals in the mice cells. It took about 10 times this amount to trigger the same signals in naked mole-rat cells.

KATE FRANCIS

The researchers determined that just a few tiny genetic changes accounted for the difference. The same pathway that detects hot temperatures also senses the hotness of spicy foods, like chili peppers (see Pepper Power). So technically, naked mole-rats could chow down on as many fiery peppers as they like without breaking a sweat—not that they ever would (they eat mainly root vegetables).

Lewin believes his findings could someday lead to new treatments for people with injuries or chronic disease. “It’s important to understand pain so that we can make better pain medications that work effectively and safely,” he says.

Why such a big difference? The researchers found that just a few tiny genetic changes explained it. And this nerve pathway doesn’t detect only hot temperatures. It also senses the hotness of spicy foods, like chili peppers (see Pepper Power). That means naked mole-rats could munch as many fiery peppers as they like without breaking a sweat. But they probably never would. (They eat mainly root vegetables.)

Lewin’s findings could someday lead to new health treatments. They could help people with injuries or disease. “It’s important to understand pain so that we can make better pain medications that work effectively and safely,” he says.

PEPPER POWER

Gary Lewin has been studying naked mole-rats for nearly a decade. In 2008, his team found that the rodents feel no pain from capsaicin—the chemical that gives hot peppers their burn—when it’s rubbed on their skin. The hotness of a pepper, related to its capsaicin level, is measured in Scoville units. The more Scoville units a pepper has, the hotter it tastes.

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PEPPER POWER

Gary Lewin has been studying naked mole-rats for nearly a decade. In 2008, his team found that the rodents feel no pain from capsaicin—the chemical that gives hot peppers their burn—when it’s rubbed on their skin. The hotness of a pepper, related to its capsaicin level, is measured in Scoville units. The more Scoville units a pepper has, the hotter it tastes.

SHUTTERSTOCK.COM

CORE QUESTION: Explain how scientists set up their experiment to learn why hot temperatures don’t cause naked mole-rats pain.

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