Figure 1.

Schematic representation of microglial functional states in the healthy murine brain. Microglia arise from erythro-myeloid precursors in the embryonic yolk sac and populate the brain rudiment early during development. Microglial cell population is maintained by self-renewal, without the contribution of bone marrow-derived progenitors. In the adult healthy brain, microglia continuously survey the brain and readily react to any potential threat to the CNS homeostasis. Phagocytic microglia can detect and quickly remove damaged or dying neurons, preventing further damage to neighboring cells. During developmental stages, microglia phagocytic capacity is particularly important to prune supernumerary synapses. Microglia has also been suggested to modulate neuronal activity by influencing synapse transmission (synaptic stripping). Under specific conditions, microglia are able to remove dysfunctional synapses by physically interacting with functional neurons.