Project Summary: Project 1 - Integrating Astrocytes into Models of Neural Circuits Regulating Behavior Astrocytes, the most abundant cells in the brain, express various receptors of neurotransmitters and neuromodulators and extend thousands of fine cellular leaflets, wrapping around the pre- and postsynaptic neuronal elements. Studies over past decades have portrayed a picture where astrocytes actively respond to both local and long projecting neuronal activities, first increasing cytosolic calcium ions (Ca2+) or other internal signals, then influencing the concentration of extracellular factors and ions and ultimately modifying its gene expression pattern and morphology. Thus, while neurons are unarguably a necessary player in neural circuits, astrocytes need to be accounted and integrated into the neural circuits to achieve a more complete understanding on how the brain works or dysfunctions. Indeed, it is appealing to consider astrocytes and neurons as a unified circuit, since they participate in the brain information processing in complementary manners in terms of both temporal and spatial domains. However, precisely how astrocytes temporally and spatially integrate the molecular signals from diverse neuronal signals, particularly during behavior, remains poorly understood. Likewise, how the diversity of astrocyte activity, in turn, influences neural circuit function on various timescales, is unclear. The hypothesis is that a deeper and more complete understanding on the astrocytes’ contribution to neural circuits can be achieved by systematically measuring, manipulating, quantifying and modeling the astrocytes’ functional and structural status in the context of controllable and quantifiable behavior tasks, which is the collective effort proposed by this U19 team. Leveraging the improved and comprehensive measurement and manipulation of (a) various neurotransmitters and neuromodulators, (b) multi-scale and multi-level anatomical information, (c) important intracellular messengers, and (d) genomic signals from the efforts in the other three projects, this project focuses on building mathematical models (Aim 1) to quantitatively interpret and predict how astrocytes integrate various neuronal signals, and how the astrocytes regulate the neural circuit in both fast-time and long-term scales. Considering that astrocytes have complex spatiotemporal dynamics and their morphologies are irregular and in close contact with diverse neurons, one needs to accurately quantify the astrocyte dynamics (Aim 2) and faithfully reconstruct the anatomy (Aim 3), to provide the necessary quantitative description of observations and the fundamental geometric constraints to the model development. Reciprocally, this project will identify knowledge gaps to suggest new experiments, make predictions to generate new hypothesis and provide quantification tools to facilitate scientific discoveries for the other three projects and more broadly for the neuroscience community.