Supplementary Figure 4: Synaptic vesicles at single and compound SLM spine synapses; related to Fig. 4.
From: Single excitatory axons form clustered synapses onto CA1 pyramidal cell dendrites
(a) Synaptic vesicle numbers (≤ 50 nm from the presynaptic active zone membrane) at single and compound synapses (from n = 195 reconstructed single connection synapses and n = 56 compound connection synapses). Left, mean number of vesicles per synapse (***two-sided Mann-Whitney test, p < 0.0001). Right, synaptic vesicle density from the same synapses (defined as vesicle number per µm2 of active zone; ***two-sided Mann-Whitney test, p < 0.0001). Bar graphs represent mean ± SEM. (b) The relationship between the number of synaptic vesicles (located ≤ 50 nm from the presynaptic active zone membrane) and the size of the active zone in single and compound synapses (Spearman correlation: single, n = 195, r = 0.84, p < 0.0001; compound, n = 56, r = 0.65, p < 0.0001; comparison between best-fit slopes, p = 0.053). (c) Synapses containing presynaptic mitochondria are associated with larger active zones (AZ) (from n = 251 reconstructed synapses: ***two-sided Mann-Whitney test, p < 0.0001), an increased number of docked vesicles per synapse (vesicles with centers ≤25 nm of the AZ; from n = 251 reconstructed synapses: ***two-sided Mann-Whitney test, p < 0.0001), and a higher density of docked vesicles (vesicles with centers ≤25 nm of the AZ normalized per µm2 of AZ; (from n = 251 reconstructed synapses: ***two-sided Mann-Whitney test, p < 0.0001). Bar graphs represent mean ± SEM.
