Examples of different types and locations of MVBs. A, B, C. Serial electron microscopy images showing a spheroidal MVB (arrows) that is isolated in the cytoplasm. Numbers in the top right-hand corner indicate the position of each micrograph in the series. Arrowhead in C points to a membrane thickening possibly representing a clathrin coat (see text for further explanation). D, E, F. Another series of images showing an MVB docked on a mitochondrion. The MVB (arrows) has several tubular expansions (t). Arrowhead in E shows the contact point between the mitochondrion and the MVB. G. Three-dimensional reconstruction of the same MVB and mitochondrion shown in D–F. H, I, J. MVBs located in a dendritic spine, an excitatory axon, and an inhibitory axon, respectively. Note that the postsynaptic density (PSD) is thick in excitatory synapses shown in H and I, while it is thin in the inhibitory synapse shown in J. Scale bar shown in J is 520 nm in A to H; 300 nm in I; 370 nm in J.