Washington, January 29 : Tiny naked mole-rats do not produce a body chemical called Substance P, which is released by pain fibres that send signals to the central nervous system in mammals as an when they make contact with things that cause long-lasting, achy pain.
This finding is important as it may one day lead to the development of new analgesic drugs for people with chronic pain who do not respond well to current medication.
Thomas Park, associate professor of biological sciences at the University of Illinois at Chicago, and Gary Lewin of the Max Delbruck Center for Molecular Medicine (MDC) in Berlin used a modified herpes cold sore virus to carry genes for Substance P to the rodents' nerve fibres.
"We were able to rescue their ability to feel pain," said Park.
The research group restored Substance P and the naked mole-rats' ability to sense the burning sensation, which is felt by other mammals upon being subjected to capsaicin, the active ingredient in chilli peppers.
The restored sensitivity was limited to just one rear foot of each tested rodent.
"They'd pull their foot back and lick it," in response to the stimulus, said Park, adding that other feet were impervious to the sting of capsaicin.
"Capsaicin is very specific for exciting the fibres that normally have Substance P. They're not the fibres that respond to a pin prick or pinch, but the ones that respond after an injury or burn and produce longer-lasting pain," said Park.
However, mole-rats remained completely insensitive to acids, which suggests a fundamental difference in how their nerves respond to this stimulus.
"Acid acts on the capsaicin receptor and on another family of receptors called acid-sensitive ion channels. Acid is not as specific as capsaicin. The mole-rat is the only animal that shows completely no response to acid," Park said.
According to the researcher, this study provides an opportunity to gain deeper knowledge about the neurotransmitter Substance P.
"This is important specifically to the long-term, secondary-order inflammatory pain. It's the pain that can last for hours or days when you pull a muscle or have a surgical procedure," he said.
Park also said that naked mole-rats provided a new model system, different from all other animals he had studied so far.
"We're learning which nerve fibres are important for which kinds of pain, so we'll be able to develop new strategies and targets," he said.
The researchers are now planning to study other animals that are closely related or unrelated to nude mole-rats, including Alaskan marmots that burrow in high CO2 environments, to examine how they have evolved similar strategies to cope with acid-rich living conditions.
The study has been published in the free-access journal PLoS Biology.