Cells of the body can now be selectively activated with ultrasonic waves. The new technique used on brain cells has been named sonogenetics. The findings are available on Nature Communications.
Sonogenetics might be reminiscent of the light-based method which is known as optogenetics whereby cell activation is done with light. The new technique uses the same type of waves dealt with in medical sonograms. The former is being described as having the upper hand over the latter though.
“Light-based techniques are great for some uses and I think we’re going to continue to see developments on that front,” says the senior author of the study, Sreekanth Chalasani, an assistant professor in Salk’s Molecular Neurobiology Laboratory. “But this is a new, additional tool to manipulate neurons and other cells in the body.”
The application of optogenetics is limited when used on brain cells: researchers sometimes have to perform surgery to be able to reach cells found in deep layers of the brain. Furthermore, light scattering while trying to activate cells is also an obstacle. To counter these difficulties, Chalasani and his team endeavoured to use ultrasound waves instead of light.
“In contrast to light, low-frequency ultrasound can travel through the body without any scattering,” he says. “This could be a big advantage when you want to stimulate a region deep in the brain without affecting other regions,” explains the first author of the study, Stuart Ibsen.
The scientists demonstrated the use of ultrasound waves in nematode Caenorhabditis elegans. They showed how low-intensity ultrasound waves were amplified by microbubbles of gas outside the worm such that the oscillations resulting therefrom would propagate into the worm in a non-invasive manner.
They also discovered that a membrane ion channel known as TRP-4 responded to the waves: when the ultrasound hitting gas bubbles caused mechanical deformations that propagated into the organism, the TRP-4 channels would open and activate the cell.
Sonogenetics has only been used on the neurones of C. elegans for now. But, it is hoped that TRP-4 could be added to any calcium-sensitive cell type in any other living thing, including humans; microbubbles would have to be injected into the blood for the waves to be propagated.
“The real prize will be to see whether this could work in a mammalian brain,” Chalasani says. “When we make the leap into therapies for humans, I think we have a better shot with noninvasive sonogenetics approaches than with optogenetics.”