We initially began studying the influence of ultrasound on neuronal activity using in vitro brain slice preparations. Here, we transmitted low-intensity, low-frequency ultrasound (LILFU) into hippocampal slices prepared from mice. The basic procedures our lab originally developed and still implements are illustrated below.
The movie below illustrates data obtained from time-lapse confocal imaging of calcium transients in hippocampal slice cultures. The movie shows that LILFU activates calcium transients in hippocampal slice cultures. A "red dot" will appear in the upper right-hand portion of the movie to indicate the onset of LILFU.
Using the methods shown above, we found that LILFU is capable of stimulating action potentials, voltage-gated sodium and calcium transients, and synaptic transmission in hippocampal brain slices. Gaining insight into how ultrasound influences neuronal activity through in vitro work permits us to i) gain insight into how mechanical forces affect neuronal activity and ii) to rapidly develop strategies for engineering methods and devices for controlling intact brain activity with ultrasound. Data from some of our published in vitro observations are illustrated below.
In a manuscript we published in PLoS One in October of 2008, we employed optical imaging to visualize voltage-gated sodium and calcium transients of neurons in response to LILFU. The figure below shows that LILFU can indeed activate voltage-gated sodium transients in neurons of hippocampal slices stained with the sodium indicator CoroNa Green. The figure also shows data obtained through whole-cell current clamp methods. Here, individual action potentials evoked by LILFU are shown below.
Using hippocampal slice cultures prepared from thy-1-synaptopHluorin mice (spH), we have also been able to show that LILFU triggers synaptic transmission at central synapses. The movie below shows LILFU stimulates synaptic vesicle exocytsosis as indicated by spH. A "yellow dot" will appear in the upper right-hand portion of the movie to indicate the onset of LILFU.
Reference: Tyler et al., 2008. Remote excitation of neuronal circuits using low-intensity, low-frequency ultrasound. PLoS One 3(10) e3511. PDF