PROJECT SUMMARY: This team initiative will provide the broad neuroscience community with a cell type-specific adeno- associated virus (AAV) armamentarium for easy and non-invasive implementation of novel and emerging molecular tools for anatomical and functional analysis of the nervous system in rodents, non-human primates, and human organoids. We will characterize engineered AAV capsids for cell type- and brain region-specific gene delivery (Aim 1). We will pair these capsids with cargos of recently optimized and newly developed sensors and effectors, largely enabled by the BRAIN Initiative, and validate their functional utility for large- scale monitoring and manipulation of brain function across species (Aim 2). Finally, we will establish an electronic AAV resource portal to catalogue and disseminate all of these tools to the broader research community (Aim 3). This proposal promises to validate a broad array of engineered systemic AAVs with access to molecularly defined neuronal cell types for delivery of BRAIN-relevant cargo and functional interrogation of brain cells across species. To maximize the utility of these tools to the neuroscientific community, we will engage in broad collaboration and dissemination. Building on the CLOVER Center’s established network of AAV production facilities, we will facilitate the broad adoption of systemic AAVs through consultation and collaboration, including provision of cost- free sample AAV preps. We will explore methodological innovations in AAV production and administration while catalyzing the early-stage adoption and validation of engineered capsids identified in this proposal by creating an electronic AAV resource for dissemination of reagents and best practices, containing catalogued AAV brain atlases and a data re-capture portal for continuous, crowd-sourced validation. The expertise and infrastructure built over the life of this proposal will form the foundation of a long-term comprehensive center for AAV BRAIN SENSUS (Safe and Effective Neuromodulator and Sensor Utilization across Species) that will open new doors for neuroscience tool validation and dissemination.