Evolution of naked mole-rats may offer clues to pain relief

Naked mole-rats evolved to thrive in an acidic environment that other mammals, including humans, would find intolerable.

How these rodents adapted to this environment may offer clues to pain relief for humans and other animals, UIC researchers say.

In the tightly crowded burrows of the African naked mole-rats’ world, carbon dioxide builds up to levels that would be toxic for other mammals, and the air becomes highly acidic. These animals freely tolerate these unpleasant conditions, says Thomas Park, professor of biological sciences.

Much of the lingering pain of an injury, for example, is caused by acidification of the injured tissue, Park said.

“Acidification is an unavoidable side-effect of injury,” he said. “Studying an animal that feels no pain from an acidified environment should lead to new ways of alleviating pain in humans.”

In a mammal’s nose, acidic fumes activate specialized nerve fibers that, in turn, stimulate nerves in the brainstem. The result: responses that protect the animal — it will secrete mucus and rub its nose, for example, and avoid the acidic fumes.

The researchers placed naked mole-rats in a system of cages where some areas contained air with acidic fumes. The animals were allowed to roam freely, and the time they spent in each area was tracked.

Their behavior was compared to laboratory rats, mice, and a closely related mole-rat species that likes to live in comfy conditions.

The naked mole-rats spent as much time in the acidic fumes as in fume-free areas, while the other animals avoided the fumes.

The researchers studied response to acidic fumes by measuring a protein that is often expressed when nerve cells fire. In naked mole-rats, no such nerve activity was found. In rats and mice, however, the nerves were highly activated.

The naked mole-rats’ tolerance of acidic fumes is consistent with their adaptation to living underground in chronically acidic conditions, Park said.

The study was supported by a grant from the National Science Foundation. Pamela LaVinka, graduate student in biological sciences, was first author on the study.