Why naked mole rats feel no pain: Secret to creature's immunity could help create new drugs for humans 

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Naked mole rats are strange-looking creatures, but their fascinating qualities do not end there.

Seemingly immune to cancer and ageing, they have a life expectancy of over 30 years, an insect-like social society dominated by a queen, and the unusual ability of being able to run backwards as fast as they can run forwards.

Now scientists have discovered the mechanism behind another of their incredible features - their inability to feel some types of pain.

This discovery could help the development of pain relief for humans.

Naked mole rats are strange-looking creatures, but their fascinating qualities do not end there. Seemingly immune to cancer and ageing, they do not feel certain types of pain, like the kind most mammals would experience from climbing over chili peppers

The researchers, led by Professor Gary Lewin from the Max-Delbrück Center for Molecular Medicine in Berlin, looked into a mechanism that causes our bodies' response to hot temperatures when our skin is sensitive, for example when we feel sunburnt.

When there is inflammation around sensory neurons, and we experience high temperatures, molecules called nerve growth factor (NGF) molecules bind to a receptor, called TrkA.

This is what happens when someone with bad sunburn gets into a hot bath.  

The naked mole rat wouldn't be bothered by this, but most animals would sense this as thermal hyperalgesia - sensitivity to temperatures when our sensory neurons are inflamed.

'The importance of increased NGF signaling during pain has recently been reinforced by the fact that blocking NGF signalling appears to be highly effective in treating pain in humans on the basis of phase 2 clinical trial data,' Professor Lewin and colleagues wrote in a new paper published in Cell Reports.

The NGT signalling kicks off a cascade of chemical signals that 'sensitize' an ion channel on the surface of the sensory neuron so that it opens. 

Once this channel opens, it causes sensory nerve firing that tells the brain to register pain at temperatures that are not normally painful.

But the researchers found for naked mole rats, a small difference in the TrkA receptor that means they do not feel the same kind of pain.

'Even though the naked mole rat's version of the TrkA receptor is almost identical to that of a mouse or a rat, it has a very significant effect on the animal's ability to feel pain,' said Professor Lewin. 

The researchers compared the gene for the naked mole rat's TrkA receptor to those of 26 other mammals, and five other African mole rat species. 

Now scientists have discovered the mechanism behind another of naked mole rats' (pictured) incredible features - their inability to feel some types of pain. This discovery could help the development of pain relief for humans

They discovered a switch of just one to three amino acid changes on one section of the naked mole rat TrkA receptor that make it less sensitive.

The new study found naked mole rats are born with roughly the same number of pain sensors as newborn mice.

The adult animals have two thirds the number of pain sensors compared to any other mammals, so it is only by adulthood that the naked mole rat's pain sensors dwindle, the researchers found.

The researchers suggest this could be an evolutionary trait, since losing these sensors might help the naked mole rats survive in their crowded underground colonies, where the close contact can become uncomfortably hot.

It is also possible losing sensory neurons as adults may help the animals conserve energy.

'They live in desert regions underground, and they have to do a lot of work to get their food,' said Professor Lewin. 

'They have the lowest metabolic rate of any mammal. 

'Evolution has shut down everything that is not absolutely necessary - including extra nerve receptors.'

Professor Lewin and his colleagues are planning future studies in mice bred to have the unique naked mole rat TrkA receptor.

'We hope to see that these modified mice will show lots of features that make naked mole rats unique,' said Professor Lewin.

One interesting feature that doesn't get as much attention is their curious teeth, which they use to dig with. Their lower incisors are permanently on show on the outside of the animal's lips and can move independently of each other, almost like a pair of chopsticks