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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 2. Astrocytes secrete signals to induce synapse maturation.

Figure 2

Astrocytes secrete molecules to convert silent synapses (synapses lacking AMPA receptors (AMPARs)) into functional synapses. At the resting potential, NMDA receptors (NMDARs) barely pass any current (not shown) in response to activation by glutamate (blue circles). This is because NMDARs are subject to a voltage-dependent magnesium block. Therefore, NMDARs rely on AMPAR activation to produce sufficient depolarization to allow cations to flow through the channel and to produce an excitatory postsynaptic current (which in turn generates an action potential (AP) that propagates along the axon, as indicated by the dashed arrow). Astrocytes secrete glypicans (green circles) to increase the surface levels and clustering of the GluA1 subunit of the AMPAR and thereby to induce excitatory synapse functionality. The neuronal receptor for the glypicans has yet to be identified, but studies in Drosophila melanogaster indicate that the protein tyrosine phosphatase receptor leukocyte antigen-related receptor (LAR) could be involved.