Figure 1. Astrocyte-mediated regulation of transmission at the tripartite synapse.

A Electron microscopic image showing a tripartite synapse in the NAc, in which a glutamatergic axospinous synapse is wrapped by astrocyte processes (scale bar corresponds to 0.5 μm). B Diagram illustrating astrocytic mechanisms of glutamate homeostasis at glutamatergic synapses. Specifically, GLT-1 on astrocytes removes synaptically released glutamate, which can be converted to glutamine within astrocytes and transported back into presynaptic terminals. xCT located at perisynaptic astrocytic processes maintains extracellular levels of ambient glutamate. C Diagram showing mechanisms of increasing Ca²⁺ in astrocytes, including ER-derived Ca²⁺ release or entry via ionotropic receptors, that play a key role in the signaling pathways employed by astrocytes to regulate glutamate transmission, including ATP-P2Y1, adenosine-A1R, glutamate-mGluR5, and glutamate-mGluR2/3 signaling pathways.