Focused Ultrasound Neuromodulation of Human In Vitro Neural Cultures in Multi-Well Microelectrode Arrays

Focused ultrasound neuromodulation. This up and coming exciting field is a topic of ongoing studies In the field of focused ultrasound, the optimal stimulation parameters for a particular application are often unknown. This study aims at a systematic determination of these parameters through empirical in vitro testing on neurons.

This method can explore the neuronal mechanism underlying focus of resound neuromodulation by enabling researcher to analyze the responses of genetically and pharmaceutically modified neurons. To begin aspirate the culture medium to fill a single well in a 24 well neuron culture plate, having embedded micro electrode arrays or MEA. After preparing 300 milliliters of degassed and deionized water, carefully fill it in the focused ultrasound or FUS transducer cone.

Using a customized threaded rod, secure the 3D printed holder to a frame. Position the frame such that the head of the FUS transducer is over the well that will be stimulated. Use a rubber band to secure paraform over the well on the 24 well MEA plate containing the medium and the human induced pluripotent stem cells or HIPSCs.

Set the FUS parameters on the transducer power output or TPO control panel. The values of the various parameters are mentioned on the screen. Next, apply coupling gel on top of the paraform over the well and lower the FUS transducer into the coupling gel ensuring contact with the gel with minimal air bubbles.

Start the FUS sonication by pressing the bottom right button on the TPO and wait at least five minutes between each round of sonication to allow the neurons to return to a baseline state. If the connection is appropriate, the trigger pulse generated by the FUS system will automatically align the FUS stimulation sequence with the MEA recording. Analyze the signal by reading the FUS sonication time with the transfer data based on the change in the firing rate associated with the FUS.

The FUS focal spot was characterized both by visualizing it on thermo chromatic sheets and through water hydrophone scanning. Post-processing steps, including filtering, thresholding, and calculating the firing rate, filtered the noise from the environment to reveal the neuronal activity changes caused by FUS. The raster plots showed the detected spikes in each channel.

The firing rate plot showed that the chosen stimulation parameters increased the neuronal firing rate. The pre FUS firing rate was 140 hertz, while the post FUS firing rate was 786 hertz with continuous wave FUS. Altering the FUS sonication mode also changed the amount of time before the neurons return to their baseline state.

It is crucial to carefully minimize bubble formation when placing the transducer onto the paraform interface. Another consideration is the electrical power delivered to the transducer. The power must be high enough to induce an effect, but must be low enough to not induce transducer or cell damage.

This technique could identify the optimal stimulation parameter to treat Parkinson's disease and other neurological disorders, eliminating risk associated with the invasive surgery, including irreversible damage, lengthy recovery, and rehabilitation time. Further efforts to uncover its mechanism and control preclinical optimization are necessary to ensure safety in future studies, including clinical trials.