I’m convinced that naked mole rats are superheroes. They are remarkably long-lived, thrive in environments low in oxygen and high in ammonia and carbon dioxide, and appear to be immune to cancer.
Scientists have now discovered the secret behind another one of their superpowers: their inability to feel certain types of pain. Naked mole rats are the only known vertebrates impervious to the pain of acid burns.
In 2008, researchers injected capsaicin, the substance that makes chili peppers painful, into the paws of naked mole rats – and the naked mole rats didn’t care.
In a new paper in Science, Ewan St. John Smith and colleagues looked for the molecular explanation of this acid insensitivity. Their first hypothesis was that naked mole rats must be missing the acid-sensing channels that regulate the activity of nociceptors, the neurons that sense painful stimuli. But this was not the case: Naked mole rats have functional acid-sensing channels, and even produce them in similar quantities as other animals.
The answer involves another type of channel, called voltage-gated sodium channels. Like the acid-sensing channels, voltage-gated sodium channels (Navs for short) help regulate the activity of neurons. When the Smith and his colleagues exposed the nociceptors of naked mole rats to acid, they discovered the signal transmitted through the Nav channels was inhibited. This inhibition prevented the nociceptor from becoming excited and firing. If a nociceptor does not fire, no pain is felt.
A search of the naked mole rat’s genome revealed two mutations in one specific Nav channel, called Nav1.7. Nav1.7 plays a crucial role in determining whether a nociceptor signals the presence of a painful stimulus to the brain. In fact, there is a rare genetic condition in humans where the Nav1.7 channel is missing, and these individuals feel no pain at all. The Nav1.7 mutations in naked mole rats inhibits nociceptors from firing when they are exposed to acid.
Naked mole rats are fast becoming one of my new favorite creatures. Don’t think of them as ugly – think of those naked, wrinkly sausage bodies as disguises for the superheroes within.