Naked mole rats don't feel pain the way we do, and now we know why

Naked mole rats, the desert-dwelling animals that look like the lovechild of an uncooked sausage and a scrotum, don’t feel certain kinds of pain — and now, scientists may have a better idea why.

The lovechild of an uncooked sausage and a scrotum

In fact, these poop-eating, subterranean creatures have a lot of enviable qualities: they can dodge cancer, live decades longer than other rodents, and go without oxygen for 30 minutes at a time. They might even have evolved a way to avoid the unpleasant, secondary pain that comes from putting heat on an injury, according to a new study.

Think of the last time you cut or burned yourself and then ran lukewarm water over the wound — the water burned and hurt the injury more than uninjured skin, right? Over the centuries of living in tunnels in East Africa, naked mole rats lost the painful sensitivity to heat that follows injuries in humans and other animals. They don’t feel this because of a tiny alteration to a molecule involved in pain sensation, according to results published today in the journal Cell Reports.

Flickr/Jedimentat44

This change blocks the cascade of signals that would otherwise make temperatures typically too low to cause pain feel like a painful burn. That means that if I were a naked mole rat, it wouldn’t hurt like hell every time I wash my hands for days after burning myself on the coffee maker. If it weren’t for their need to eat their own feces or the fact that they look like a pudgy salami with teeth, I’d consider letting a radioactive naked mole rat bite me.

It makes sense that animals living in crowded, underground tunnel networks where temperatures stay at a toasty 86 degrees Fahrenheit wouldn’t want to feel ongoing, burning pain after a little scrape. But scientists have been stumped as to how naked mole rats actually lost their sensitivity to heat around an injury, since the molecules that detect burning pain in other animals remain intact.

I'd consider letting a radioactive naked mole rat bite me

In rats, mice, and people, painful sensitivity to heat following an injury occurs because hurt tissue squirts signaling molecules onto pain-sensing nerves. This starts a domino effect that makes the nerve cell send pain signals in response to lower levels of heat, which it senses using the same molecule that detects the substance that makes chili peppers burn. That’s why lukewarm water feels painfully scalding on injured skin. The naked mole rats don’t feel that.

Because experiencing pain requires a sequence of events in the body, like a chain of dominoes, the researchers thought they might be looking too far down the chain. So they moved up the line to a signal released by damaged tissue that docks onto the surface of pain-sensing nerves. The researchers compared the protein sequence for the naked mole rat dock to the sequence in 26 other mammal species and five non-naked African mole rat species. They discovered that between one and three spots on the naked mole rat molecular dock differ from those of its African mole rat relatives. This modification is like a piece of plywood between the dominoes in the cascade; if the first domino falls, it doesn’t matter — the rest won’t.

But the site isn’t totally unusable, it just needs a stronger push, which is why the naked mole rats are still able to grow a normal nervous system. If this feedback loop were completely dysfunctional, the naked mole rat might not grow a normal network of neurons. As it is, it actually has fewer strands of nerves involved in sensing pain than other African mole rats.

These findings are a pretty impressive example of how a change to a single molecule can result in a species-wide adaptation. If scientists figure out how to harness this ability in humans, it could help people with serious injuries or autoimmune disease feel less pain. Personally, if I were to acquire the mole rat’s superpowers, I might once again brave making coffee with my nemesis, the French press. Though not feeling pain comes with some pretty serious downsides — namely, in this case, that I wouldn’t be protecting my burned fingers from the too-hot glass nearly as carefully. That is one challenge these near-indestructible creatures don’t face.

By Naked mole rats don't feel pain the way we do, and now we know why

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