We thought we already knew everything there is to know about these ugly, hairless animals. But now US and German researchers have even more amazing news for us.

They found that naked mole-rats can survive conditions that would kill other mammals - including humans - within minutes.

When oxygen levels fall to a life-threatening level, the subterranean animal simply slows down its heart rate and switches to another metabolism system.

Even if there is no oxygen present at all, naked mole-rats can survive.

They do lose consciousness, but as soon as they get a sniff of oxygen, they start stirring again as if nothing happened. There is no damage as long as the oxygen break doesn't last longer than 18 minutes.

"This is just the latest remarkable discovery about the naked mole-rat, a cold-blooded mammal that lives decades longer than other rodents, rarely gets cancer and doesn't feel many types of pain," says Thomas Park of the University of Illinois at Chicago, co-author of the study.

Park has studied the strange species for 18 years.

Naked mole-rats live in unventilated burrows and tunnels underground, packed in with hundreds of colony mates. In such conditions, a lack of oxygen occurs quite often. That's why the species had to adapt.

The study appeared  in the journal "Science" on Thursday.

Mammals aren't made for a world without oxygen.

When the supply stops, the oxygen in their brain only lasts for a few more seconds. Within one or two minutes, energy-carrying molecules like ATP are used up and brain cells start to die.

Within a minute or so, mice and other mammals pass the point of no return. Too many brain cells have died.

Even when re-exposed to ambient air, the animal will have severe damages for the rest of its life such as paralysis or a mental disability - if it survives at all. 

Naked mole-rats, however, have found a way to bypass their oxygen-dependent metabolism.

When oxygen is low, their brain cells switch over to burning fructose instead of glucose, because this pathway doesn't need any oxygen.

The animals even have a special fructose pump in their brain cells that has been found in other mammals' intestine only.

"The naked mole-rat has simply rearranged some basic building-blocks of metabolism to make it super-tolerant to low oxygen conditions," says Park.

Researchers say they have only observed this kind of fructose-burning metabolic pathway in plants before.

There are other, non-mammal animals that can survive long periods without oxygen.

North American freshwater turtles and goldfish, for example, spend their winters in oxygen-lacking, ice-covered lakes and ponds.

But even though naked mole-rats with their 18-minute survival time pale compared to turtles and some fish species, researchers are still impressed with the findings, Jay Stolz of the University of Nebraska, US, and Grant McClelland of the McMaster University in Hamilton, Canada, who were not involved in the study, write in an accompanying article in "Science:"

"It is astounding by mammalian standards."

Researchers hope that the naked mole-rat will show them a way to treat patients suffering from oxygen deprivation as it occurs in heart attacks or strokes.