Fig. 1.4.1.64. Not all mushroom-shaped dendritic spines containing perforated postsynaptic densities are equipped with a spine apparatus. Squares in a transparent 3D reconstruction of a small volume (106 µm3) neuropil of the rat hippocampal stratum radiatum represent the total number of mushroom-shaped dendritic spines (45); of these, only 31 (69%) contained a spine apparatus (red squares). Analysis of comparable volumes from the same localization in two other animals showed a similar result—from 31 only 19 (61%) and from 47 only 21 (45%). (Hippocampus, rat.)