Fig. 3: Majority of spines are contacted by nodes.

a Two-color STED image of morphological interaction between astrocytic spongiform domain (green) and a dendrite (magenta). b Images of spines contacted by nodes, shafts, and spines lacking an astrocytic structure in their vicinity. c Percentage of spines contacted by nodes, shafts, and spines lacking an astrocytic structure in their vicinity. The majority of spines are contacted by at least one node (n = 188 spines from 21 slices). d Image of extracellular space (black) surrounding a synapse (gray) and astrocyte (yellow). Right image indicates the putative identity of the synaptic components. e Frequency distribution of node area. Nodes were highly variable in size (n = 103 nodes from 21 slices). f Correlation between node area and spine head area. Node area was strongly positively correlated with spine head area (n = 103 structures from 21 slices; Spearman r = 0.669, ****p (two-tailed) < 0.0001). g Frequency distribution of fraction of spine coverage by astrocytic node, showing that spine surfaces were mostly node-free (n = 103 spines from 21 slices). h Correlation between coverage fraction and spine head area. Large spines had similar coverage fractions as small spines (n = 103 spines from 21 slices; Spearman r = 0.086, p (two-tailed) = 0.38). i Two-color STED image of morphological interaction between astrocytic spongiform domain (green) and an axon (magenta). j Images of boutons contacted by nodes and boutons lacking an astrocytic structure in their vicinity. k Percentage of boutons contacted by nodes and boutons lacking an astrocytic structure in their vicinity. Node-contacted boutons account for the majority of boutons (n = 35 boutons from 5 slices). l Correlation between node area and bouton head area. Bouton area was positively correlated with node area (n = 35 structures from 7 slices; Spearman r = 0.5689, ***p (two-tailed) = 0.0004). m Correlation between fraction of bouton coverage by astrocytic node and bouton area. Large boutons had similar coverage fractions as small boutons (n = 35 boutons from 5 slices; Spearman r = 0.2874, p (two-tailed) = 0.0941).