After years of study and research, the secret of what causes sensitivity and pain in humans and other mammals may ultimately rest on the tiny nerve endings found in the unique snout of the star-nosed mole.
In a study published in the journal PLOS ONE, researchers at the University of California, Berkeley, and Vanderbilt University say that the star shaped tip of the mole’s nose has a higher proportion of touch-sensitive nerve endings than pain receptors, and that further study may lead to an understanding of how these sensations are detected in our cells.
“By studying the star-nosed mole, we identified candidate genes that may mediate touch and pain,” said lead author Diana Bautista. ”These genes represent new potential targets for the development of much needed drugs and therapies to treat chronic pain.”
Touch and pain are closely intertwined sensations, but researchers say very little is known about how these sensations are detected in human cells. That’s why they turned to the star-nosed mole; it possesses one of the most sensitive tactile organs known in the animal kingdom.
The semi-aquatic mammal is a burrowing animal, known to reside in a network of narrow underground tunnels. Existing in an environment of almost complete darkness, the star-nosed mole’s poorly-developed eyes render it virtually blind, making the sensitivity of its snout an integral part of its survival.
The mole’s ability to touch 13 separate areas of the ground every second allows it to consume 8 separate prey items in less than 2 seconds, earning it the distinction in Guinness World Records as the world’s fastest forager.
And with the star on its nose having the highest density of nerve endings known in any mammalian skin (over 100,000 fibers in a patch of skin less than half an inch or one centimeter in diameter), the animal was a perfect candidate for further study.
What researchers discovered was that the nerve endings of the star shaped nose were significantly enriched in neurons sensitive to light touch, with a lower proportion of neurons meant to detect and respond to pain.
They also found that the touch and pain receptors they identified in the mole were detected in the sensory receptors of mice and humans, suggesting that these receptors are likely to be more common in other mammals as well.
According to Bautista, the results of the study highlight how examining other species can reveal fundamental aspects of biology common across different animals.
To find the biological building blocks that endow the creature with such high tactile sensitivity, scientists looked at the 22 tactile “rays” that ring the mole’s nostrils, and the tens of thousands of domed epidermal touch organs — called Eimer’s organs — that cover them.
Using various stains and irritants, Bautista and her team noted that the difference in reaction to heat and sensitivity found in the various sections of the tactile “rays” appeared to be happening at the cellular and molecular level. That discovery, researchers believe, may one day provide important clues that can lead to the identification of the molecular mechanisms that regulate the transmission of touch and pain in humans.
“Our results emphasize the utility of examining both traditional model organisms and less common species that may provide important clues to sensory system function,” wrote Bautista.
A research team at the University of Illinois at Chicago also turned to a mole in their research into the treatment of chronic pain.
A study of naked mole-rats found that the rodents not only survived, but thrived, in an acidic environment that other mammals, including humans, would find intolerable. It’s an ability that researchers say may hold important clues to unraveling the mystery of chronic pain.