Ultrasound pulses to the brain send mice into a hibernation-like state.
For many animals, life is a cycle of abundance as well as scarcity. Hibernating creatures move underground during the winter, slowing their metabolism so that they can make it to spring without food. Even laboratory mice, if deprived of food, can enter a state called torpor, a kind of standby mode that reduces energy.
Here’s something humans have long imagined about themselves: If we ever leave this planet and travel into space, we’ll run out of time. Science fiction writers imagine a mysterious technology that keeps humans in stasis, able to survive for centuries in silence before emerging into new life. For now, it’s a technology that’s out of reach.
But as scientists work to understand states like torpor and hibernation, details about how the brain controls metabolism have emerged. The researchers reported. Journal Nature Metabolism On Thursday, they were able to send mice into a torpor-like state by targeting a specific area of the brain with small bursts of ultrasound. It’s not clear why ultrasound has this effect, but the findings suggest that studying the neural circuits involved in torpor may reveal ways to manipulate metabolism outside the lab.
Ultrasound devices, which generate high-frequency sound waves, are known for their imaging powers. But they have also been used by neuroscientists to stimulate neurons. Properly tuned, sound waves can penetrate deep into the brain, said Hong Chen, a professor of biomedical engineering at Washington University in St. Louis and author of the new paper. In 2014, William Tyler, now at the University of Alabama, Birmingham, and colleagues applied ultrasound to a sensory region of the brain and found that It enhanced the subject’s sense of touch. There is a growing body of work Exploring ultrasound as a treatment For disorders like depression and anxiety.
Curious about the brain region that controls body temperature in mice, Dr. Chen and his colleagues created miniature ultrasound mousecaps. The device trained six bursts, each consisting of 10 seconds of ultrasound, on a selected area of the rat’s brain. (Researchers who study the brain with ultrasound must tune their instruments carefully to avoid heat that can damage tissue).
The researchers observed that the mice stopped moving. Measurements of their body temperature, heart rate and metabolism showed marked declines. After the ultrasound burst, the rats remained in this state for about an hour and then returned to normal.
By looking closely at the neurons involved in this response, the researchers identified a protein in their brain membranes, TRPM2, that appears to be sensitive to ultrasound. When the researchers reduced the levels of the protein in the mice, the mice became resistant to the effects of ultrasound.
This is an important step toward understanding how ultrasound affects neurons, said David Foloni, a researcher at the Icahn School of Medicine at Mount Sinai in New York City who studies the brain using ultrasound. The details have been largely elusive.
But it’s also possible that the heat generated by the ultrasound, and not just the ultrasound itself, is affecting TRPM2 in the mice’s brains, a point Masashi Yanagisawa and Takeshi Sakurai of the University of Tsukuba in Japan made in separate interviews. was raised Both have studied neurons in this area of the brain, and they are related to states of torpor. Both may be at play, Dr. Chen said.
In one of the most disturbing parts of the study, the researchers tested to see if animals that don’t normally experience torpor – mice – would wake up when the brain region was stimulated with ultrasound. behaved differently. In fact, they seemed lethargic, and their body temperature had dropped.
“We have to be careful with the rat data,” cautioned Dr. Chen. So far they only have information about temperature, not metabolic rate and other factors.
Could ultrasound be a way to alter the metabolism of large animals that have no history of torpor like humans? “It’s an interesting idea,” said Dr. Sakurai.
“At this stage,” he said, “that’s an unanswered question.”