Key Points
- Researchers conducted a preclinical study using ultrasound neuromodulation to send rodents into a hibernation-like state called “torpor.”
- Mammals and some birds enter torpor to conserve energy in harsh environments.
- The effect could be prolonged when controlled by an automated body temperature detector.
Induction of a Torpor-Like Hypothermic and Hypometabolic State in Rodents by Ultrasound
The research team led by Hong Chen, PhD, at Washington University in St. Louis (WUSTL) recently conducted a preclinical study using ultrasound neuromodulation to send rodents into an unusual metabolic condition called “torpor.” To survive harsh environments, mammals and some birds enter torpor to conserve energy; it decreases both their metabolism and their body temperature.
Although news outlets were quick to pick up that this type of research was proposed in the 1960s as a promising way to send astronauts deep into space, a more practical and common application could be helping patients with a heart attack or stroke survive by slowing metabolism and disease progression.
After building wearable ultrasound transducers for three types of rodents, first author Yaoheng (Mack) Yang, PhD, a postdoctoral researcher, and the team applied transcranial ultrasound stimulation to an area of the brain called the preoptic area (POA) in the hypothalamus. Torpor was induced when the ultrasound stimulation suppressed metabolism, reduced body temperature, decreased heart rate, and switched the body’s energy production to fat. The effect lasted longer than 24 hours in the animals when the ultrasound stimulation was controlled by an automated body temperature detector. When the ultrasound was discontinued, body temperature returned to normal.
Importantly, one of the rat models does not naturally enter torpor, yet the team was able to induce the hibernation state with focused ultrasound.
“While these findings in the non-torpid animals suggest the possibility of similar effects in humans, further research is necessary to determine the safety and feasibility of ultrasound-induced artificial hibernation in humans,” said Dr. Yang.
The WUSTL team, which included researchers from biomedical engineering, psychology, pathology and immunology, and anesthesiology and pain medicine, is calling the procedure “ultrasound-induced hypothermia and hypometabolism,” or UIH.
To determine the molecular mechanism behind the UIH effect, the researchers studied how the POA neurons were activated and correlated it with the expression of the gene (TRPM2) for ultrasound-sensitive ion channels in that area. They revealed that focused ultrasound activated the POA neurons that highly expressed the TRPM2 ion channel. The dorsomedial hypothalamus (a downstream brain region) and brown adipose tissue were also involved as the downstream brain region and effector tissue.
See Nature Metabolism (Open Access)
See Nature Metabolism’s News and Views Commentary: “Hypometabolism with the Speed of Ultrasound.”
See Media Coverage in the New York Times, New Scientist, the Daily Beast, and the many other outlets listed on WUSTL’s press release.