This is a fascinating development, mostly because the subjects, rats, do not normally hibernate. The corollary is that other mammals that don’t hibernate (such as humans) may also be open to this procedure. The implications for the treatment of medical emergencies and deep space exploration are enormous.
Have you ever wondered how some small animals can survive in extreme cold temperatures, or when there isn’t enough food around? They have a trick up their sleeves, or rather, in their bodies! Some mammals and birds can go into a torpor-like state, where their body temperature and metabolic rate drop to conserve heat and energy. Scientists have tried inducing this state before, but it wasn’t safe or non-invasive.
But guess what? Hong Chen, an associate professor at Washington University in St. Louis, and her team, found a way to induce a torpor-like state in mice and rats by using ultrasound. They targeted the hypothalamus preoptic area in the brain, which regulates body temperature and metabolism. That’s right – they used ultrasound on the brain!
The team created a wearable ultrasound device that stimulated the neurons in the hypothalamus preoptic area. When stimulated, the mice showed a drop in body temperature of about 3°C for an hour. During this time, their metabolism changed from using both carbohydrates and fat for energy to only fat, a key feature of torpor. Their heart rates also decreased by 47%, all while at room temperature.
As the acoustic pressure and duration of the ultrasound increased, so did the depth of the lower body temperature and slower metabolism. Pretty cool, huh? It’s known as ultrasound-induced hypothermia and hypometabolism (UIH). The team also developed an automatic closed-loop feedback controller to achieve stable ultrasound-induced hypothermia and hypometabolism by controlling the ultrasound output. The controller set the desired body temperature lower than 34°C, which was reported as critical for natural torpor in mice. This is a significant breakthrough in the field of torpor research, and it can have implications for space travel and human health in the future.
To activate ultrasound-induced hypothermia and hypometabolism (UIH), Chen’s team stimulated neurons in the hypothalamus preoptic area of the brain.
They observed an increase in neuronal activity in response to each ultrasound pulse that aligned with the drops in body temperature in the mice. By activating these neurons, they induced a torpor-like state that mimics what happens naturally in hibernating animals. Chen and her team also identified the molecule that allows these neurons to activate with ultrasound.
By conducting genetic sequencing, they found that ultrasound activates the TRPM2 ion channel in hypothalamus preoptic area neurons. This channel is an ultrasound-sensitive ion channel that contributes to the induction of UIH.
In the rat, which doesn’t naturally go into torpor or hibernation, the team delivered ultrasound to the hypothalamus preoptic area and found a decrease in skin temperature and about a 1°C drop in core body temperature, matching that of a natural torpor state. UIH offers a potential way to safely and noninvasively induce a torpor-like state in humans. This technology has implications for space travel and preserving the health of patients with life-threatening conditions. Ultrasound therapy can noninvasively reach deep brain regions with high spatial and temporal precision, making it an ideal method for inducing UIH.
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