Relationships between spine size and the location of presynaptic cells. (A) The soma of the postsynaptic neuron represents the center of the three dimensional coordinates. The presynaptic soma (xpre, ypre, zpre), the innervated spine (xsp, ysp, 0), and their projections in the XY and XZ planes are shown. (B) XY-plane-projected distribution of presynaptic neurons (xpre, ypre) and the spines they innervated (xsp, ysp). Black, blue, orange, and red closed circles represent cells innervating spines of sizes 0-0.1 μm3 (black open circles), 0.1-0.2 μm3 (blue open circles), 0.2-0.3 μm3 (orange open circles), and >0.3 μm3 (red open circles), respectively. (C) Histograms of the lateral distance between the postsynaptic and presynaptic somata (left), ; the lateral distance between the dendritic spine and the presynaptic soma (middle), ; and the straight-line distance of the dendritic spine from the presynaptic soma (right), . Black, blue, orange, and red bars indicate spines of sizes 0-0.1 μm3, 0.1-0.2 μm3, 0.2-0.3 μm3, and >0.3 μm3, respectively. *P < 0.05 (one-way ANOVA followed by Tukey's test). (D) Histograms of xpre. Black, blue, orange, and red bars indicate the presynaptic cells innervating the spines of sizes 0-0.1 μm3, 0.1-0.2 μm3, 0.2-0.3 μm3 and >0.3 μm3, respectively. * P < 0.05 (Mann-Whitney U test).