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. Author manuscript; available in PMC: 2015 May 14.
Published in final edited form as: Nat Rev Neurosci. 2013 Apr 18;14(5):311–321. doi: 10.1038/nrn3484

Figure 1. Astrocytes instruct structural synapse formation by the secretion of several molecules.

Figure 1

Astrocytes secrete the thrombospondins (purple circles), which are reported to interact with neuroligins, the α2δ-1 voltage-gated calcium channel subunit and integrins to induce excitatory structural synapse assembly. Astrocytes also secrete hevin (orange circles) and SPARC (red circles). Hevin promotes the formation of excitatory synapses, whereas SPARC antagonizes the synaptogenic function of hevin. Both neurexins and neuroligins have been identified as binding partners for hevin, and SPARC can bind integrins. It is thought that the thrombospondins and hevin bind to and cluster trans-synaptic adhesion molecules to induce the formation of structurally normal but postsynaptically silent excitatory synapses. The dashed arrow indicates action potential (AP) propagation, which induces glutamate release from synaptic vesicles. NMDAR, NMDA receptor.