How microglia sense and regulate neuronal activity in the adult brain

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PROJECT SUMMARY/ABSTRACT Microglia are innate immune cells of the central nervous system, which interact with neurons in the adult brain. Microglial receptors and pathways have a demonstrated ability to alter complex network function. This process begins with microglia sensing specific neuronal signals. However, the downstream mechanisms used by microglia to enact specific responses/outcomes is not well understood. The purpose of this research is to understand how microglia sense neuronal activity during hyperactivity (e.g., seizures) and hypoactivity (e.g., anesthesia), which may then trigger unique functional responses to alter neuronal circuits in the adult brain. ATP purine signaling during hyperactivity is a well-documented signal for microglia to interact with neurons in seizure, reducing seizure severity. However, the complexity of microglial intracellular (secondary messenger such as Ca2+ signaling) responses to ATP is only partially understood. Unique intracellular signaling cascades in microglia may differentially influence their functional responses. These pathways will be interrogated using acute brain slice and in vivo two-photon imaging along with a suite of new genetic and virus-based tools to uncover how the calcium pathway of microglia in particular informs seizure responses. During hypoactivity, a loss of norepinephrine signaling allows microglia to better interact with neurons under anesthesia. The purpose of these interactions for network function is unknown, but will be dissected using in vivo two-photon imaging of microglia- neuron dynamics in the intact brain, coupled with 3D-electron microscope reconstruction of highly detailed structural interactions. Previous experience using chemogenetic and conditional knockout approaches to alter microglia function are also utilized to dissect specific pathways regulating hypoactive neural circuit responses. Ultimately, determining how microglia regulate neuronal function, including underlying mechanisms and their impact on circuitry, is essential to fully understand how microglia are integrated into the complex neuronal circuits as they become dysregulated in brain diseases, such as seizures and sleep disorders.