It is a classic science fiction trope: Astronauts on an interstellar journey are kept in sleek, refrigerated pods in a state of suspended animation. Even though such pods stay purely fictional, scientists have pursued study into inducing a hibernation-like state in humans to lessen the harm brought on by healthcare circumstances such as heart attacks and stroke, and to minimize the strain and expenses of future lengthy-distance space sojourns.
In a study published now in Nature Metabolism, scientists report that they can trigger a equivalent state in mice by targeting portion of their brain with pulses of ultrasound. Some authorities are calling it a key technical step toward attaining this feat in humans, whereas other people say it is a stretch to extrapolate the outcomes to our species.
“It is an wonderful paper,” says Frank van Breukelen, a biologist who research hibernation at the University of Nevada, Las Vegas and co-authored an editorial accompanying the study. The function builds on a flurry of current research that pinpoint particular populations of neurons in a area known as the preoptic region (POA) of the hypothalamus. These cells act like an on-off switch for “torpor”—a sluggish, power-saving state the animals enter when they’re dangerously cold or malnourished. In prior research, scientists genetically engineered these neurons to respond to light or specific chemical compounds, and identified they could bring about mice to enter a torpid state even when they have been warm and properly-fed. Such invasive strategies cannot be simply translated to individuals, nevertheless, Breukelen notes. “That’s definitely not going to take place in individuals.”
The new ultrasound study, led by bioengineer Hong Chen and her group at Washington University in St. Louis needed no genetic engineering. Chen knew from prior study that some neurons have specialized pores known as TRPM2 ion channels that modify shape in response to ultrasonic waves, such as the subset of POA cells that controls mouse torpor. To see what impact that had on the animals’ behavior, her group subsequent glued miniature, speakerlike devices on the heads of mice to concentrate these waves on the POA.
In response to a series of three.two-megahertz pulses, the rodents’ core physique temperatures dropped by about 3°C. The mice cooled off by shifting physique heat into their tails—a classic sign of torpor, Bruekelen notes—and their heart prices and metabolisms slowed. By automatically delivering extra pulses of ultrasound when the animals’ physique temperatures started to climb back up, the researchers could hold the mice in this torpid state for up to 24 hours. When they silenced the minispeakers, the mice returned to regular, apparently with no ill consequences.
Chen’s group then repeated the experiment in 12 rats—which do not naturally go into torpor in response to cold or meals scarcity—and identified a equivalent impact, though their physique temperatures only dropped by 1°C to 2°C. The researchers say this suggests the strategy could function even in animals that do not ordinarily hibernate.
Breukelen says his self-confidence in the team’s outcomes is strengthened by the reality that when the researchers directed the ultrasound to other brain regions, the mice didn’t seem to enter a torpid state. That suggests the animals’ lowered metabolism was certainly brought on by stimulating especially the neurons in the POA, and not just by “scrambling” brain functioning. “I do not believe anybody desires a therapy that relies on just turning off the brain, and consequences be damned,” he says. He’s also encouraged that the researchers re-designed the exact same impact in rats. Even though humans do not naturally hibernate, the capacity is identified in species from practically every single mammalian lineage, from Madagascar’s fat-tailed dwarf lemur to the arctic ground squirrel. Maybe humans, like the rats, also possess a hidden capacity for getting into a thing akin to hibernation, he says.
Other people are not convinced. Shaun Morrison at Oregon Wellness & Science University doubts the scientists definitely observed torpor in the mice. Ultrasound stimulation warms up the brain, he says, so it is feasible the researchers have been in reality activating temperature-sensitive neurons in that area, causing the animals to reduce their physique temperatures in response. Even if the impact is true, he’s skeptical that we’ll be making use of ultrasound to place astronauts into suspended animation anytime quickly. People’s brains are a lot larger than the brains of mice and the POA is buried deeper, Morrison notes, creating it a lot far more challenging to target with the minispeakers Chen and her colleagues employed. “This ultrasound strategy is quite unlikely to function in humans in the way it does in mice.”