Squirrels Shed Light on Human Hibernation

That haunting image from science fiction movies showing astronauts hibernating during long space voyages may not be as far-fetched as it seems.

We would be a bit closer if someone could figure out exactly how some other animal, say a ground squirrel, can put itself to sleep for the cold months of winter and then rouse itself in time for the first spring munchies.

No one is seriously working toward hibernating astronauts at the moment, because there's so much about it that we don't understand, but lots of scientists are taking a close look at ground squirrels, which may hold the key.

The 13-lined ground squirrel, the little critter seen around golf courses and lawns throughout Middle America, is on center stage in a number of laboratories because of its extraordinary ability to hibernate.

And because in some critical ways, it's a lot like us.

Super Squirrel

Where the research will lead is conjecture at this point, but it's quite possible that if we can figure out how the squirrel works its magic, we might be able to extend the shelf life of human organs during transplant procedures, and that alone would be a major breakthrough.

But that's not all.

"If we understood how these animals naturally undergo such extreme changes every year, like clockwork, we might be able to come up with therapies for humans and other animals that could help in trauma situations," says Hannah V. Carey, a professor of biosciences in the School of Veterinary Medicine at the University of Wisconsin, Madison. It might even help in controlling the bulging human waistline because "these animals are great examples of gaining weight, and losing weight, and gaining weight, and losing weight," she says.

All that interest is centered on a remarkable little critter that many consider a pest and often confuse with gophers. The 13-lined ground squirrel, so named because of 13 lines down it's back and sides, measures only about 6 inches long.

But each winter it survives for up to six months by lowering its heart and metabolic rates and reducing its body temperatures to just above freezing, which would be fatal to humans and nearly all other animals. Periodically, the squirrel rouses itself for reasons that are not clearly understood, and then returns to a state of torpor.

What the squirrel is doing, she says, is readjusting it's systems "to slow down the fire, slow down the metabolic burn, so it doesn't use as much energy."

It is one of the great physiological marvels of the natural world because the squirrel is able to protect and preserve its critical organs despite extreme biological insults over a period of several months.

Cool Organs

Carey believes the squirrel may hold the key to keeping vital human organs, like livers, viable for longer periods, thus greatly facilitating organ transplants. Currently, a human liver begins going downhill within a few hours after being extracted from a donor. What's amazing about the ground squirrel is it survives for months at body temperatures that are nearly identical to the near-freezing temperature at which human organs are kept during transplanting procedures.

Carey and a colleague, Jim Southard, a surgeon in the university's division of transplantation, have a room full of ground squirrels on the Wisconsin campus, and their research so far has had very promising results. The researchers harvested about 20 livers from hibernating squirrels to see how long the organs would remain viable while outside the animal.

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