Our knowledge about the complex interplay between the various brain cell types (neuronal and non-neuronal) is still rudimentary. These interactions are disrupted in every neurological disorder. Our laboratory is interested in elucidating these multicellular and complex interactions that occur during brain pathogenesis. Recent innovations in live imaging and optical probes are allowing sophisticated interrogation of the structural and functional cellular changes that occur in pathological processes. Our goal is to develop and implement such methodologies for advancing our understanding of the physiology of different brain cells and how they interact in their native unperturbed microenvironment and during homeostatic perturbations. I have been involved in developing pioneering methods of long term longitudinal cellular imaging in the living brain with photon microscopy, now widely used in the neuroscience community and we have made important biological discoveries using live optical microscopy. Specifically, I was involved in the first study determining the stability and turnover rates of synapses (Grutzendler et. al, Nature 2002) and microglia dynamics (Davalos et al, Nat. Neurosci 2005) in vivo, two highly-cited and a landmark studies in the neurosciences. Our lab has also made fundamental discoveries related to microvascular pathology (Lam et al. Nature, 2010) and development (Whiteus et al. Nature 2014). We have also contributed to novel understanding of the role of microglia in Alzheimer’s disease (Condello et al. Nat. Comm 2014 and Yuan et. al. Neuron 2016). Finally, we have recently pioneered methodologies for in vivo label-free imaging of myelinated axons (Schain et al. Nat. Medicine 2014). Thus, our laboratory is well positioned to continue advancing the understating of neuro-glio-vascular interactions in health and disease. This proposal aims to put together our expertise in cellular in vivo imaging with exciting new transgenic mice, calcium optical sensors and intravital dyes to precisely demarcate and probe pericyte function and structure in vivo. Pericytes have been notoriously difficult to study given ambiguities about their identity and lack of in vivo reporters. We have recently challenged many of the assumptions in the field with regards to pericyte’s contractile role in vasomotion (Hill et al. Neuron 2015). In summary, the overall goal of our laboratory is to develop and utilize innovative technologies that will allow advancing a broad understanding of the physiological interactions between the diverse brain cell types and how these are disrupted in a variety of developmental, injury-related and degenerative conditions (in particular Alzheimer’s disease).