Naked mole rats, like most creatures, don't like to be pinched or pricked—but just try to get one to yelp by rubbing lemon juice or red-hot chili peppers over a cut. It won't.
That's because the hairless, finger-size rats are numb to the burning sensation that almost every other mammal feels when exposed to acids and hot peppers.
New research published this week in the journal PLoS Biology begins to unravel the mechanisms that make the mole rats impervious to these types of pain.
Previous research found that the animals lack a key messenger that carries the signal of burning pain through the nervous system.
In the new study the researchers reactivated the neurotransmitter on one foot of test rats, which got them to react to chili pepper exposure but not acids.
Further tests revealed that the naked mole rats are completely oblivious to acid, which is likely an evolutionary adaptation to their crowded, carbon dioxide-rich underground-living conditions.
The researchers also found that nerve connections in the naked mole rat's spinal column are different than those of any other animal.
The findings may lead to new treatments for human sufferers of dull, steady post-surgery pain, according to Thomas Park, a neurobiologist at the University of Illinois in Chicago who led the study.
The nerve fibers that carry information about achy pain are the same ones that carry information about acids and capsaicin—the active ingredient in chili peppers, he noted.
"What we need to do is understand how [the mole rat] solved that problem and how we can use that information to come up with new strategies to treat ... pain," Park said.
(Related news: "Feeling No Pain: New Form of Rare Gene Disorder Decoded" [December 13, 2006].)
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