In science fiction, space crews are often spared the boredom and inconvenience of long-distance space travel by being placed into a state of suspended animation. Now this goal may have come a step closer after scientists showed that hibernation can be artificially triggered in rodents using ultrasonic pulses.
The advance is seen as significant because the technique was effective in rats – animals that do not naturally hibernate. This raises the prospect that humans may also retain a vestigial hibernation circuit in the brain that could be artificially reactivated.
“If this proves feasible in humans, we could envision astronauts wearing a helmet-like device designed to target the hypothalamus region for inducing a hypothermia and hypometabolism state,” said Hong Chen, an associate professor at Washington University in St Louis, who led the work.
The team first identified a specific group of neurons in a deep brain region called the hypothalamus preoptic area, which were found to be involved in regulating body temperature and metabolism during hibernation. They showed that, in mice, these neurons could be artificially activated using ultrasound, delivered non-invasively through a helmet.
When stimulated, the mice showed a drop in body temperature of about 3C for about one hour. The mice’s metabolism also shifted from using both carbohydrates and fat for energy to only fat, a key feature of torpor, and their heart rates fell by about 47%, all while at room temperature.
The scientists also developed an automatic closed-loop feedback system that delivered an ultrasound pulse to keep the mice in the induced torpor if they showed signs of warming up. This allowed the mice to be kept at 33C in the hibernation-like state for 24 hours. When the ultrasound system was switched off, they woke up again.
The experiments, described in the journal Nature Metabolism, showed that the same device worked in rats, which had a 1C drop in core body temperature when the same brain region was targeted. Chen said the result was “surprising and fascinating” and the team planned to test the technique in larger animals.
In humans, inducing a torpor-like state has potential medical applications, with some suggesting that slowing down metabolism could buy critical time for treating life-threatening conditions such as heart attack and stroke. “By extending the window for medical intervention, this technique offers promising prospects for improving patients’ chances of survival,” said Chen. “Additionally, the non-invasive nature of the technique opens the possibility of developing wearable ultrasound devices, such as helmets, for easy access in emergency situations.”
Prof Martin Jastroch, of Stockholm University, who was not involved in the research, described the work as a breakthrough. “Everything they see recapitulates what you see in nature,” he said.
“They can also do this in rats, which is quite exciting,” he added, saying that “the chance is quite high” the same technique would, theoretically, work in humans. “We might have some residual abilities there. Before this paper no one was even thinking of how you could experiment with that in safe manner.”