Focused ultrasound facilitated adenoviral delivery for optogenetic stimulation

Optogenetics is a recently developed technique that has been widely implemented in the field of neuroscience. Channelrhodopsins (ChR), i.e., proteins that function as optically activated ion channels, are introduced into neurons either by viral transduction or transgenic manipulations. Recent advances in focused ultrasound (FUS) offer an alternative, non-invasive approach to carrying out viral transduction in the brain. In this study, we propose a FUS-based, non-invasive adenoviral delivery scheme that is suitable for optogenetic applications. Wild-type mice were used in this study, and each animal was sonicated using a single-element FUS transducer (center frequency 1.5 MHz). The acoustic parameters used for each sonication are: peak-rarefactional pressure 0.55 MPa, pulse length 10 ms, pulse repetition frequency 5 Hz, and a duration of 120 s. Viral vectors (both AAV1 and AAV9) were mixed with in-house manufactured polydisperse microbubbles prior to intravenous injections. Animals were survived for 12 days after sonication and electrode (with optic fiber) was implanted for electrophysiology recording. Upon optical stimulation, neuronal depolarization was observed in mice that received FUS-facilitated AAV transduction. In addition, fluorescence imaging revealed abundant ChR expression in the FUS sonicated brain regions. In conclusion, the successful non-invasive AAV delivery can provide an alternate and safer route for Channelrhodopsin neuronal transduction for optogenetic stimulation.