Figure 1.

Typical coxal terminal. (A) Cross section of terminal in normal saline containing mitochondria (m), synaptic vesicles, and two dense bodies at active zones (arrows). (B) Active zone in normal saline demonstrating dense body, made up of the dense body base (large arrow) and filamentous cap (small arrows). Note that the postsynaptic muscle fiber (p) extends a finger-like projection to the active zone. (Inset) Dense body base sectioned horizontally, parallel to plasma membrane. (C) Active zone in normal saline demonstrating attachment of dense body plate to the presynaptic membrane (arrow). Note the double lobed appearance of dense body base (D–F, arrowhead also). (D) Active zone in normal saline sectioned slightly tangentially to the plasma membrane to demonstrate the attachment of a subpopulation of vesicles to the dense body by thin fibrils. (E and F) Active zones exposed to 18 mM Ca²⁺ saline for 10 min, demonstrating many vesicles “docked” at the plasma membrane under the dense body plate (large arrows). Note the attachment of the vesicles to the plate by thin fibrils in E (small arrows). (G) Active zone of shi retinula cell terminal exposed to 29°C to induce vesicle depletion, followed by exposure to 26°C for 1 min. Note the membrane emanating from the plasma membrane adjacent to the dense body base (large arrows). The dense body plate (small arrows) appears to have been displaced away from the plasma membrane by the invaginating membrane. [Bars: A, 1 μm (×30,000); C, 100 nm (×75,000); B and D, 100 nm (×90,000); and E–G, 100 nm (×135,000).]