Figure 3.

Presynaptic axons. (A) Three-dimensional (3D) reconstructions of CA3-to-CA1 axons (Schaffer collaterals). (B) 3D reconstructions of axons with vesicles (yellow) and associated postsynaptic partners (dendritic spine, gray; PSD surface, red). Typical single synaptic boutons (SSB) have a single postsynaptic partner, multisynaptic boutons (MSB) have more than one postsynaptic partner, and nonsynaptic boutons (NSB) contain vesicles but have no postsynaptic partners. Also illustrated are small dense core vesicles (dcvs, dark blue), mitochondria (mito, pale blue), and a multivesicular body (mvb, dark green with brown vesicles). (C₁) 3D reconstruction of a proximal CA3 pyramidal cell dendrite (blue) and a large mossy fiber bouton (translucent yellow), which contains numerous mitochondria (yellow) and vesicles (green). The cut-away in C₂ shows synapses (red) onto multiple dendritic spines, some of which are highly branched. The bouton also forms nonsynaptic cell adhesion junctions (fuchsia). (D) Electron micrograph through inhibitory presynaptic boutons (purple) that form symmetric synapses (red arrows) on the soma of a CA1 pyramidal cell. Scale bar, 500 nm. (E) 3D reconstruction of four complete inhibitory synaptic boutons (purple) interspersed with glial processes (green) on the surface of a CA1 pyramidal cell soma (gray). The magnifications of all 3D images in A–C have been rescaled to match the 1-µm scale bar in E. (Panel A is from Shepherd and Harris 1998; reprinted, with permission, from the authors; B is from Sorra et al. 2006; reprinted, with permission, from the authors; the image in panel C is modified from a supplemental movie by Rollenhagen et al. 2007; reprinted, with permission, from the Journal of Neuroscience © 2007; panels D and E are from Ledoux and Woolley 2005; reprinted, with permission, from the Journal of Neuroscience © 2005.)