A lemur that hibernates is strange and cute enough. But studying its lethargic state may provide a clue to sending humans on long-distance space travel or healing the ravages of heart attacks, stroke and head trauma, according to researchers at Duke University.
The western fat-tailed dwarf lemur, a pocket-sized nocturnal primate native to Madagascar, is the closest genetic cousin of humans to hibernate for long periods, a discovery made by a German research team in 2004.
The revelation that primates hibernated led to a happy coincidence at Duke, which happens to have a lemur center and a sleep laboratory. Researchers there soon found two more Madagascar lemur species that hibernated.
Dr. Andrew D. Krystal, director of the medical school's sleep lab, became intrigued. He brought it up with one of the directors of the lemur center during the pair's weekly bicycle ride: What happens to lemurs when they tamp down their metabolism to a state of torpor? What are their brain waves like? Do they sleep?
The answer Krystal got was essentially, “Beats me.”
Research has shown sleep is crucial for recharging the body's metabolic batteries, and chronic deprivation can change food intake, cause weight gain, lead to insulin sensitivity and affect hormones. What if lemurs didn't need much sleep because they hibernated? Could it answer questions about human physiology?
"It is the closest genetic relative to humans that hibernates and is therefore the most likely to be providing useful information to understanding things like what is the capacity to induce hibernation-like states in humans,” said Krystal, a psychiatrist.
“If we wanted to travel to some point in outer space that took 100 years, how could we possibly do it?" Krystal said. "We would have to induce a period of hibernation that would allow a person not to need to function for a period of time in order to get there and survive and return.”
More terrestrially, a torpid state could help medical interventions for a heart attack, for example. “If you could drop the cellular demand for oxygen, you could then have somebody go in and open up that blockage and not have much damage to your heart,” said Krystal. “The same would be true of a stroke, or traumatic injury to a part of the body, particularly the brain, which is very sensitive to hypoxia.”
What Krystal's team found turned what’s known about mammal hibernation on its head, according to a study published online Wednesday in PLOS One. The primates, which hibernate in warm climates, have opposite sleep patterns to those in freezing climates, with implications for temperature regulation and metabolism.
“These animals hibernate in climates that get quite warm,” Krystal said. “They get over 90 degrees during the day and they get down in the 40s at night.”
The Arctic ground squirrel, the more frequently studied mammal, doesn’t appear to sleep during its winter hibernation. But the squirrels will spontaneously kick up their metabolic engines occasionally, then fall into a state of sleep without rapid eye movement. Their metabolism seems to “wake up” to go into non-REM sleep, and it seems to have something to do with temperature regulation.
Sleep appears "so important to these animals that they arouse out of their torpor, and it’s a metabolically expensive thing to do,” Krystal said. “There’s got to be a good reason for it, and it may not be the sleep, but sleep seems to be linked to the process.”
In toasty warm periods of the lemur hibernation, however, the pocket primates readily fell into REM sleep, a period when mammals are known to suspend temperature response, the study found.
That kind of information about body temperature, metabolism and sleep is crucial to knowing what could happen to humans if researchers unlock the key - possibly a genetic one - to inducing hibernation in humans.
“There are all kinds of interesting possibilities that open up that sound a bit like science fiction,” Krystal said. “But I think fundamentally we’re motivated by the medical applications. This is the long-term view of why we’re doing this.”