Dysbindin-deficient excitatory synapses have bigger but fewer vesicles in hippocampal CA1. (A; top) Electron micrographs depicting several asymmetrical synapses within CA1 in the ventral hippocampus. Double arrowheads indicate individual asymmetrical synapses. (bottom) Presynaptic terminals and adjacent dendritic spines. Arrowheads indicate docked vesicles; arrows mark the edges of the active zone/PSD complexes. Bars: (top) 500 nm; (bottom) 100 nm. (B) Distribution of vesicle sizes shows larger vesicles in sdy neurons (black) than in WT (gray). Gaussian fitting was performed. (bottom) The mean vesicle diameter of both cell types (WT, 44 ± 0.1 nm; sdy, 47 ± 0.1 nm; n = 1,015 vesicles from 121 WT synapses and 1,102 vesicles from 103 sdy synapses). (C) Comparison of four parameters, i.e., density of docked synaptic vesicles in active zone (WT, 20.5 ± 0.7 docked vesicles per μm; sdy, 20.2 ± 0.9 docked vesicles per μm), density of reserve pool (RP) vesicles in presynaptic terminal (WT, 110 ± 4 reserve pool vesicles per μm²; sdy, 86 ± 5 reserve pool vesicles per μm²), PSD thickness (WT, 44.2 ± 0.7 nm; sdy, 49 ± 1.0 nm), and synaptic cleft width (WT, 20.5 ± 0.2 nm; sdy, 16.0 ± 0.2 nm) in WT and sdy mice. ***, P < 0.001. Error bars indicate the mean ± SEM.