Ultrasound Brain Pulse Puts Mice into a Hibernation-Like State | Chemistry

This is a classic science fiction trope. Astronauts during interstellar travel are kept in a sleek refrigerated pod in suspended animation. While such pods are only fictional, scientists are suggesting that humans can mimic hibernation to reduce damage from medical conditions such as heart attacks and strokes, as well as reduce the stress and expense of future long-distance spaceflights. We have been conducting research to induce such a state.

In a study published today, natural metabolismscientists report can cause a similar condition in mice. Target parts of the brain with ultrasound pulses. Some experts say it’s a major technological step toward achieving this feat in humans, while others say the results are a stretch to extrapolate to our species.

“It’s a great paper,” says biologist Frank van Breukelen, who studies hibernation at the University of Nevada, Las Vegas, and co-authored the editorial that accompanied the study. These cells, located in a region of the hypothalamus called the preoptic area (POA), act as an on-off switch for “lethargy,” the sluggish, energy-saving state that animals enter when they’re dangerously cold or malnourished. works like Scientists have genetically engineered these neurons to respond to light and certain chemicals, which can put mice into a coma even if they are warm and well-fed. I discovered something. “That doesn’t really happen to humans.”

The new ultrasound study, led by bioengineer Hong Cheng and her team at the University of Washington in St. Louis, didn’t require genetic engineering. Chen knew from previous research that some neurons have specialized pores called pores. TRPM2 ion Channel Cells that change shape in response to ultrasound, including a subset of POA cells that control dormancy in mice. To see how it affects the animal’s behavior, her team then attached a small speaker-like device to the mouse’s head to focus these waves on the POA. rice field.

In response to a series of 3.2 MHz pulses, the core body temperature of rodents decreased by approximately 3°C. By transferring body heat to the tail, the mice lowered their body temperature—a classic sign of coma—and slowed their heart rate and metabolism, Breukelen said. By automatically sending additional ultrasound pulses when the animal’s body temperature began to rise, the researchers were able to keep the mice in this stunned state for up to 24 hours. When I turned off the mini-speaker, the mouse returned to normal with no apparent ill effects.

Cheng’s team then repeated the experiment with 12 rats.Similar effects were found, even though these animals did not spontaneously enter a coma in response to cold or lack of food, and their body temperature dropped only 1 to 2°C. The researchers say this suggests the technique could work in animals that don’t normally hibernate.

Breukelen said the team’s confidence in the results was bolstered by the fact that the mice didn’t appear to be stupor when the researchers hit other areas of the brain with ultrasound. This suggests that the animal’s hypometabolism was indeed caused by specifically stimulating neurons within the POA, rather than simply “scrambling” brain function. “I don’t think anyone wants a cure that relies on simply turning off brain function. The results are abhorrent,” he says. He also encouraged researchers to replicate the same effect in rats. Humans do not naturally hibernate, but this ability is found in species in nearly every lineage of mammals, from the fat-tailed dwarf lemurs of Madagascar to the ground squirrels of the Arctic. Perhaps humans, like rats, have a hidden ability to enter a state similar to hibernation, he says.

Others are not convinced. Sean Morrison of Oregon Health and Science University doubts that scientists really observed lethargy in mice. Because ultrasound stimulation warms the brain, the researchers may have actually activated temperature-sensitive neurons in that area, causing the animals to cool down in response, he said. Even if the effect is real, I’m skeptical about using ultrasound to put astronauts in suspended animation any time soon. Morrison notes that the human brain is much larger than the mouse brain and the POA is buried deeper, making it much more difficult to target with the mini-speakers Chen and his colleagues used. . “This ultrasound technique is very unlikely to work in humans as it does in mice.”