Hibernating squirrels may hold clue to post-stroke therapy

Scientists in Alaska say they have figured out how to make squirrels hibernate, a process that could be used to preserve brain function in humans who suffer strokes or heart attacks.

But the technique only worked in squirrels who were awakened by researchers during their hibernation season, not outside normal hibernation times, said the study in The Journal of Neuroscience.

Researchers at the University of Alaska, Fairbanks, studied arctic ground squirrels, giving them a caffeine-like substance to awaken them from hibernation.

Another substance was given to them at various times of the year to see if it could stimulate parts of the brain that encourage a molecule called adenosine to attach itself to the receptors, causing sleepiness.

"When a squirrel begins to hibernate and when you feel drowsy it's because adenosine molecules have attached themselves to receptors in your brain," Tulasi Jinka, lead author of the study, said.

Adenosine slows nerve cell activity. Animals in hibernation experience very low body temperatures and take in little oxygen, but they suffer no brain damage.

If scientists could master this process in humans, they could potentially prevent damage caused by severe trauma, when people stop breathing or suffer sudden heart attack or stroke.

But those days are still a long way off.

The researchers found that they could induce torpor, or the state in which oxygen consumption falls to 1 percent of resting metabolic rate and core body temperature approaches freezing, consistently only in squirrels who were awoken from hibernation in the midst of their sleeping season.

Essentially, they could wake up a hibernating squirrel and then get it to go back to sleep.

However, when they tried to induce hibernation outside of the regular season, it worked in just two of six squirrels during the early hibernation season, but not in any during the summer when squirrels do not hibernate.

"We show for the first time that activation of the adenosine receptors is sufficient to induce torpor in arctic ground squirrels during their hibernation season," Jinka says.

The researchers are unsure what causes the brain to become sensitive enough to adenosine that it can enter a state of hibernation when the season is right. Their next step is to test the process in rats, whose systems are more similar to those of humans.

"Understanding the neuroprotective qualities of hibernating animals may lead to development of a drug or therapy to save people's lives after a stroke or heart attack," Kelly Drew, senior author and professor in the UAF's Institute of Arctic Biology, says.