Neuronal network activity controls microglial process surveillance in awake mice via norepinephrine signaling

Microglia are resident immune cells that dynamically survey the brain parenchyma, interacting with neurons in both health and disease. However, it is still unclear how neuronal network activity drives microglial dynamics. Utilizing in vivo two-photon imaging of microglia in awake mice, we found that inhibition of neuronal activity under general anesthesia dramatically increased microglial process surveillance. Accordingly, both sensory deprivation and optogenetic inhibition of local neuronal network activity in awake mice resulted in similar increases in microglial process surveillance. We further determined that reduced norepinephrine signaling is responsible for the observed increase in microglial process surveillance. Our results demonstrate that microglial process dynamics are directly influenced by neural activities through norepinephrine signaling in awake animals and indicate the importance of awake imaging for studying microglia-neuron interactions.