Layout of the active zone at the frog’s NMJ.

<p>(A) Composite diagram viewed in the active zone’s transverse plane. The main body of the AZM is between the two synaptic vesicles (SV) docked on the presynaptic membrane (PM). At the core of the main body are the beam, step and mast, each connected to the docked vesicles by the horizontally arranged ribs, spars and booms, respectively. Pegs, which were not included in this study (but see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069410#pone.0069410-Harlow1" target="_blank">[8]</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069410#pone.0069410-Nagwaney1" target="_blank">[10]</a>) connect the ribs to channels in the presynaptic membrane, while pins, which are AZM macromolecules away from the AZM’s main body connect the docked vesicles directly to the presynaptic membrane. A topmast links the mast to an undocked vesicle. Non-AZM macromolecules connect the docked vesicles to nearby undocked vesicles and are similar in appearance to macromolecules linking undocked vesicles to each other. (B) Schematic of a short segment of the active zone showing the 3D relationship of AZM macromolecules to docked vesicles and those undocked vesicles linked to topmasts, with indicators of the active zone’s horizontal, median and transverse planes. The color code for the structures shown here is the same for all Figures in this report. A complete description of the organization of AZM and non-AZM macromolecules can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069410#pone.0069410-Szule1" target="_blank">[11]</a>.