Arctic Squirrel Surgery Could Yield Medical Solutions

T O O L I K  L A K E, Alaska, Oct. 13, 2003 -- The chunky squirrel was irritated and alert within the metal trap. It had been lured in by carrots but now it gnawed at the cage with its teeth and pushed with its paws to escape. But before it would be freed, it would become part of an experiment that could someday help suppress human appetites, or even save lives on the battlefield.

Ryan Long, an undergraduate student at the University of Alaska, Fairbanks, strode across the shrubby tundra to the trap at the top of the small slope and gently picked it up to inspect the squirrel.

"Oh, look at that! It's a new one," he said, noticing the squirrel had no scar on its belly.

A few hours later the hefty little animal was lying flat and unconscious on a table under a scalpel.

Long was working with Brian Barnes, a biologist at the University of Alaska, Fairbanks who has been trapping and performing surgery on these bulkiest of all squirrels — the arctic ground squirrel — for nearly a dozen years on the slopes of northern Alaska.

The purpose, he explains, is to understand and perhaps tap into the squirrel's unusual ability to hibernate at below freezing temperatures for eight months every winter.

Supercooled Squirrels

Although many mammals hibernate, no one does it quite like the arctic ground squirrel, or the sik-sik, as they're called by the local Inuit people here. (The name mimics the squirrel's rasping, chirp-like call.).

After becoming plump from summer feeding, these animals tuck in for the winter in 2-foot deep burrows at around late August. Then for eight months, they allow their body temperatures to drop to as low as 26 degrees Fahrenheit — six degrees below freezing. Every three weeks or so they wake up for a few hours and sleep in a normal state before dropping back into hibernation.

Barnes believes the behavior could hold medical solutions for the future, from better preservation of donated organs to stabilizing injured soldiers until medical care is available, to developing a natural appetite suppressant modeled after the same mechanisms that allow squirrels to fast for the entire, long arctic winter.

"In hibernation, their body doesn't demand energy … the rate of blood flow to their brain drops down to just a few percent of normal and when they rewarm they have no brain damage. Their organs are in this very low temperature state that even under ideal circumstances for donor organs in humans, tissues can only stay viable for a day or four days at most, but squirrels can remain at this temperature for weeks on end," he said.

Preserving the body at below freezing temperatures is no easy feat and Barnes' research shows the little animal does this by supercooling its blood.

You can supercool water by filling a test tube and then slowly freezing it. If the water is kept very still, it may remain in liquid state as the temperature drops below freezing. But it will instantly freeze if disturbed or if contaminated by a particle that then acts as a template for more ice to form.

In a similar way, the arctic ground squirrel manages to keep its body fluids flowing despite below freezing temperatures. Barnes is trying to understand how the squirrels manage to purify their blood of any particles that might trigger freezing.

"Supercooled squirrel blood is vulnerable to being nucleated by a crystal and flash freezing — and if that happens to these guys they die," he said.

Under the Knife

In order to understand the squirrel's tricks, Barnes closely monitors their temperatures year-round in the wild, which is why the captured squirrel was lying flat on a table below Barnes' scalpel.

Long and Barnes had placed the animal in a large pickle jar, pumped in general anesthesia — the same gas once commonly used in human surgery — until it gradually stopped scratching the side and went limp.

After removing the squirrel from the jar and placing it on a table, Barnes laid a blue paper sheet over the squirrel's shaved belly and delicately cut an opening in its abdominal cavity with surgical scissors. Into the incision he pushed an Oreo-sized rubber coated instrument that would float freely within the squirrel's abdomen, then sewed up the cut.

The device was programmed to record the squirrel's internal temperature every 20 minutes for two years so when Barnes tries to recapture the animal in subsequent summers, he can remove the instrument and download the data.

Over the seasons, Barnes has performed this same procedure on dozens of squirrels captured from Alaska's North Slope and has several screens full of data from instruments recovered from the animals. It's from these numbers that Barnes has begun to understand the squirrel's unique rhythms.

Solutions for Shooting Victims, Astronauts

The next step, he says, is to find ways to mimic the squirrel's tricks. For example, victims of a shooting or a heart attack usually have only so much time — often referred to as the "golden hour" — before their blood pressure plummets and brain damage sets in. Placing the victims into a squirrel-like hibernation state might help extend that critical period.

"If we could inject these victims with a cocktail of drugs, whatever they turn out to be that squirrels use, we could extend that golden hour to a day," said Barnes. "There's a lot of interest in this right now by the military."

Similar applications might also allow astronauts remain at a suspended state, requiring little food or water during many-year voyages to distant planets. At a lesser level, Barnes believes the squirrels' hibernation state could be somehow administered to help obese patients place their appetites on hiatus until they drop to normal weights.

Last year, Long and Barnes added another instrument to the captured squirrel. Long attached a collar equipped with an optical sensor that recorded every two minutes whether the squirrels were out feeding or huddled in their burrows. Long is finding that the squirrels feed less and huddle in their burrows more on rainy days.

Since the animals only have two to three months of summer to fatten up for the long winter months, there is concern that a changing climate could threaten the animals since one of the predicted effects of warming in Alaska's arctic is more frequent rainfall in the summer.

"That has a potential to affect their natural history," said Long. "We'll see."

But for now, at least the captured squirrel would be fine. He was shaken but recovering nicely from his surgery. Barnes fed him a carrot for his troubles and the next day Long released the animal back onto the tundra where it would soon burrow in for the winter and do its part for science.