PROJECT SUMMARY/ABSTRACT Optogenetics provides a precise deconstruction of neural circuits by optically manipulating the activity of opsin-expressing neurons with fast temporal responses and neuron-type specificity. A critical challenge of delivering light in the brain for in vivo optogenetics arises from the poor penetration of photons in biological tissue due to the scattering and absorption of light. As a result, in vivo optogenetic stimulation in the deep brain usually requires invasive procedures, such as craniotomy and intracranial implantation of optical fibers. The very invasiveness of these procedures also precludes easy repositioning and volume adjustment of the illuminated region in the same subject. Several strategies have been employed to address the challenges above. Red-shifted and ultrasensitive opsins enable transcranial optogenetics, yet light must travel through all superficial brain tissues with significant power attenuation, heating to other brain structures, potential off-target effects, and an inability to reposition the manipulated brain regions. Tapered optical fibers and reconfigurable nanophotonic circuits enable dynamic illumination across multiple brain regions but still require invasive implantation of photonic devices. Recently the Hong lab demonstrated “sono-optogenetics”, a minimally invasive method for optogenetically manipulating neural activity in vivo via brain-penetrant, focused ultrasound (FUS). Central to this method is mechanoluminescent nanoparticles (MLNPs), which can be delivered intravenously, charged by 400-nm light when passing through superficial vessels, pumped by the heart into cerebral vessels, and then gated by FUS to emit 470-nm light locally for opsin activation, all without exiting the blood circulation. Based on these advances, we propose a rapid brain-wide optogenetic screening approach by producing on-demand light emission at any location or depth in the mouse brain. The long-term objective of this proposal is to noninvasively produce on-demand light emission patterns at any location or depth in the mouse brain for rapid brain-wide optogenetic screening of different brain regions. Specifically, the Hong lab aims to develop a toolbox of MLNPs with distinct emission spectra matching different opsin variants, bright mechanoluminescence, and favorable in-vivo circulation half-life. We will characterize and validate their spectral and biophysical properties by constructing an intravital light source with on-demand emission patterns in the brain of live mice. We then seek to use the FUS-mediated intravital light source to optogenetically stimulate multiple brain regions in the same mouse, thereby fulfilling the dynamic selection of illuminated brain regions. The Butts Pauly lab will facilitate the Hong lab in the design of FUS protocols, ensuring minimal neuromodulatory effects by direct FUS stimulation of the brain. Finally, to demonstrate the unique strengths of this approach in addressing neuroscience challenges, the Hong and Chen labs will screen different brain regions that have been found to store opiate-associated memories in the same mouse brain for dissecting their contributions to the animal’s drug-seeking behavior. The proposed method will provide a valuable tool for the broader neuroscience community to rapidly screen different brain regions underlying a certain behavior or pathology of interest in the same animals.

PROJECT NARRATIVE Optogenetics enables temporally precise, neuron type-specific manipulation for dissecting the complex neural circuitry with visible light, but is limited by the invasiveness of light delivery methods and an inability to reposition the illuminated regions in the brain. To address these challenges, we propose a rapid brain-wide optogenetic screening approach by producing on-demand light emission at any location or depth in the mouse brain with brain-penetrant focused ultrasound (FUS) and circulation-delivered mechanoluminescent nanoparticles (MLNPs). This project will provide a valuable tool for the broader neuroscience community to rapidly screen different brain regions for their contributions to a certain behavior or pathology of interest, such as the drug seeking behavior, in the same animals.