Bidirectional Microglia-Neuron Communication in the Healthy Brain

Figure 2

Neuron-to-microglia purinergic signaling regulates microglial extension and retraction. (1) In the healthy brain, microglia exist in close proximity to neurons. (2) In the event of neuronal injury, neurons release purines including ATP which can be degraded by endogenous enzymes into ADP and adenosine (magnification at top right). (3) Released purines diffuse in the extracellular space and can activate P1 (A3) and P2 (P2Y12) receptors on microglia that act in concert (magnification in center). (4) Purinergic activation leads to microglial branch extension towards the injury site. (5) Following microglial activation, adenosine can also activate A2a receptors that mediate microglial branch retraction.