Fig. 1.

Regulation of microglial dynamics by norepinephrine (NE)-β₂ adrenergic receptor (β₂-AR) signaling. During wakefulness, tonic activation of NE neurons in the LC releases NE in the brain. Binding of NE to the β₂-ARs on microglia restricts microglial surveillance and ramification, injury responses, and microglia–dendrite contacts. Under anesthesia, reduced NE neuronal activity decreases the levels of NE in the brain, releasing the inhibition of microglia by β₂-AR signaling, thereby enhancing microglial surveillance and ramification, injury responses, and microglia-dendrite contacts.