Scientists, led by an Indian-American researcher, have for the first time developed a way to selectively and noninvasively activate brain, heart, muscle and other cells using ultrasonic waves.
The new technique, dubbed sonogenetics, has some similarities to the burgeoning use of light to activate cells in order to better understand the brain.
This new method – which uses the same type of waves used in medical sonograms – may have advantages over the light-based approach – known as optogenetics – particularly when it comes to adapting the technology to human therapeutics, researchers said.
“Light-based techniques are great for some uses and I think we’re going to continue to see developments on that front,” said Sreekanth Chalasani, an assistant professor in Salk Institute for Biological Studies, senior author of study.
“But this is a new, additional tool to manipulate neurons and other cells in the body,” said Chalasani.
In optogenetics, researchers add light-sensitive channel proteins to neurons they wish to study.
But using an optogenetics approach on cells deep in the brain is difficult: typically, researchers have to perform surgery to implant a fibre optic cable that can reach the cells. Plus, light is scattered by the brain and by other tissues in the body.
“In contrast to light, low-frequency ultrasound can travel through the body without any scattering,” Chalasani said.
“This could be a big advantage when you want to stimulate a region deep in the brain without affecting other regions,” said Stuart Ibsen, a postdoctoral fellow in the Chalasani lab and first author of the work.
Chalasani and his colleagues first showed that, in the nematode Caenorhabditis elegans, microbubbles of gas outside of the worm were necessary to amplify the low-intensity ultrasound waves.
“The microbubbles grow and shrink in tune with the ultrasound pressure waves. These oscillations can then propagate noninvasively into the worm,” said Ibsen.
Next, they found a membrane ion channel, TRP-4, which can respond to these waves. When mechanical deformations from the ultrasound hitting gas bubbles propagate into the worm, they cause TRP-4 channels to open up and activate the cell.
The team tried adding the TRP-4 channel to neurons that don’t normally have it. With this approach, they successfully activated neurons that don’t usually react to ultrasound.
So far, sonogenetics has only been applied to C elegans neurons. But TRP-4 could be added to any calcium-sensitive cell type in any organism including humans, Chalasani said.
Then, microbubbles could be injected into the bloodstream, and distributed throughout the body – an approach already used in some human imaging techniques.
Ultrasound could then noninvasively reach any tissue of interest, researchers said.
The study was published in the journal Nature Communications.