“Rods” Connect Vesicles to the Active Zone.

To simplify the description, we show cross-fractures where the plasma membrane and the vesicle are imaged simultaneously. Moreover, the filaments extending from the vesicle into the cytoplasm are colored cyan and the “rods” connecting the vesicle to the active zone yellow. Panels A–B show synaptic vesicles connected to the plasma membrane (Ppre) by rods oriented perpendicular to the plane of the membrane. Rod lengths are ∼20 nm in A and ∼15 nm in B. Independent of their length, however, the intra-membranous particles pointed by the arrows indicate that both rods transverse the plasma membrane at the ends. Panel C shows a vesicle connected to the active zone by rods ∼26 nm in length. A distinct kink in the mid-section, and small particles associated with the end that transverse the membrane (arrow), characterizes this rod. Panel D shows a vesicle connected to the E face of the active zone by two parallel rods (yellow). Panel E shows a rod connecting the vesicle to the P face of the plasma membrane. This rod has a domain protruding side ways into the cytoplasm (arrow). Panels F and H show synaptic vesicles connected by two parallel rods to the E face of the active zone. The arrow in F points to a distinct particle in the mid-section of the rod. Bars: Panels A–C = 45 nm; panels C–H = 35 nm.