Fig. 8. Astrocytic nodes are likely functional component of excitatory tripartite synapses.

a Confocal Ca²⁺ signal in node mapped onto STED image of spine morphology. b A STED image of YFP-labeled neuron and GCaMP6s-expressing astrocyte. c Spontaneous Ca²⁺ traces from ROIs shown in b. Note that nodes exhibit unique activation patterns. d–f Left: A STED images of YFP-labeled neurons and GCaMP6s-expressing astrocytes. Right: Ca²⁺ activity mapped onto dendritic morphology, where the Ca²⁺ event remained confined to a single node (d), where two perisynaptic nodes were co-active (e) or where a Ca²⁺ wave appeared to propagate within the local astrocytic network (f). g Percentage of perisynaptic Ca²⁺ events confined to single nodes or involving multiple nodes, showing that majority of Ca²⁺ events was confined (n = 61 events from 30 slices). h Correlation between spine size and area under curve (A.U.C.) of the node Ca²⁺ event. Large spines were associated with large Ca²⁺ events in nodes (n = 26 structures from 24 slices; Spearman r = 0.453, *p (two-tailed) = 0.0201). i Summary schematic of the tripartite synapse micro-environment consisting of a presynaptic bouton, dendritic spine, astrocytic node, shaft, loop and extracellular space (ECS). Nodes appear as the functional astrocytic component of excitatory tripartite synapses, which may provide the anatomical basis for synapse-specific communication.