Figure 4.

Presynaptic active zone (AZ) and vesicles. (A) Presynaptic dense projections (dp), a postsynaptic density (PSD), and the “intercleft line” (iL) at cerebellar synapses, revealed by ethanolic phosphotungstic acid. (B) Two serial sections through a parallel fiber synapse on a dendritic spine (Sp) in cerebellar cortex illustrate docked synaptic vesicles (green), which have no cytoplasm between the membrane of the vesicle and the AZ membrane (red arrows). The small black arrow points to a vesicle close to the membrane, but not docked. (C) Hippocampal CA3→CA1 synapse; note the docked vesicle (curved arrow, red arrow) and a presynaptic endocytic zone identified by a coated pit (straight arrow). (D) Large clear vesicles (arrows) and a DCV (red arrowhead) at the presynaptic AZ, and nondocked small synaptic vesicles in the reserve pool (arrowheads) of a CA3 mossy fiber bouton synapsing with a large dendritic spine (SP). (E) Small DCVs (red arrowheads) colocalize with small clear vesicles at a hippocampal CA1 spine synapse; and pre-embedding immunogold labeled for Piccolo (F) and Bassoon (G). (H) Bassoon localized to the AZ. (I) Post-embedding immunogold labeling for the big potassium channel (BK) located at the presynaptic active zone of a synapse on a small dendritic spine in s. radiatum of area CA1 (double-headed red arrow). (J) Positions of gold particles were compiled from the postsynaptic to presynaptic side; the glutamatergic NMDA receptor concentrated on the postsynaptic side, whereas BK channels concentrated on the presynaptic side (gold particles for NMDA are not visible in I). (K) Post-embedding immunogold labeling for CAST. Gold particles have been colored red for emphasis; original version of boxed region is shown in L. (M) Quantitative distribution of CAST with distance (in nanometers) from the presynaptic plasma membrane (arrow on x-axis). (N) Puncta adherens (PA) adjacent to the synaptic active zone (delimited beneath the PSD by triangles and line) of a large CA1 dendritic spine. (O) Silver-enhanced immunogold labeling for the cell adhesion molecule β-catenin, at the edge of an AZ on a cerebellar dendritic spines. All images have been scaled to match the 100-nm bar in C. (Panel A is adapted from van der Want et al. 1984; reprinted, with permission, from Elsevier © 1984; panel B is from Xu-Friedman et al. 2001; reprinted, with permission, from the author; panel C is from Harris and Sultan 1995; reprinted, with permission, from the author; panel D is from Henze et al. 2002; reprinted, with permission, from the author; panel E is from Sorra et al. 2006; reprinted, with permission, from the author; panel F is from Zhai et al. 2001, panels G and H are from Tao-Cheng 2007; reprinted, with permission, from Elsevier © 2001; panels I and J are from Hu et al. 2001; reprinted, with permission, from the Journal of Neuroscience © 2001; panels K–M are modified from Siksou et al. 2007; panel N is from Spacek and Harris 1998; reprinted, with permission, from the author; panel O is modified from Uchida et al. 1996.)