Hong Kong team reports ultrasound and nanostructure brain stimulation in mice

A research team at The Hong Kong Polytechnic University combined low-intensity ultrasound with engineered hollow silica nanostructures (tiny hollow particles) to stimulate specific brain regions in mice, according to a report by Phys.org. The study, titled "Sono-mechanical nanostructures-enabled sustained precise ultrasound brain stimulation," was published in Nature Communications. Lei Sun, a professor in the Department of Biomedical Engineering and Sports Technology and director of the Research Center for Non-invasive Brain Computer Interface at the university, led the team, Phys.org reported.

Parkinson's disease is linked mainly to the gradual loss of dopamine-producing nerve cells (dopamine is a chemical messenger in the brain) and affects the brain systems that control movement, often causing tremor, stiffness, slowness and balance problems, according to the report. Current treatment usually relies on medicines such as levodopa, which can improve symptoms, especially in earlier stages, but whose benefit may become less consistent over time, the report stated. For some patients, deep brain stimulation (DBS) offers another option, but this involves surgery to place electrodes deep inside the brain, according to the report.

Conventional transcranial ultrasound (delivered through the skull) penetrates deeply and can be delivered noninvasively, but its spatial resolution is typically limited to millimeter or centimeter scales, making selective activation of small groups of neurons difficult, Phys.org reported. Earlier nanoparticle- or nanobubble-assisted approaches improved localization, but their instability in living tissue limited their usefulness for long-term applications, according to the report. The hollow silica nanostructures used by Sun's team persisted in the mouse brain for more than nine weeks while remaining responsive to ultrasound, the report said.

That persistence allowed repeated stimulation of targeted brain regions, including the motor cortex, striatum, ventral tegmental area and subthalamic nucleus, without genetic modification and without repeated administration into the brain, according to the report. Ultrasound stimulation of the nanostructure-targeted subthalamic nucleus increased dopamine signaling, which the report said suggested the approach activated pathways affected in Parkinson's disease. Treated mice also showed better preservation of dopamine-related neurons, and similar benefits were seen in a second Parkinson's model, according to the report.

Phys.org described the research as a proof of concept for chronic, localized and minimally invasive neuromodulation (changing nerve-cell activity) using ultrasound and hollow silica nanostructures. The report said the method may achieve some DBS-like effects without implanted electrodes. It also said the work addresses a central challenge in translating such approaches. The reported results were in mice; the report described no tests in humans.