Fig. 4.

Ultrastructure of contacts between the B2 bipolar dendrites and cone and rod terminals. A,B, Cone terminals. Presynaptic and postsynaptic membranes are smooth and arched with a cleft of constant width (∼20 nm) that contains filamentous material. Presynaptic densification is evident, but postsynaptic densification is less prominent.C, D, Rod terminals. Glial wrappings (g) make windows; contacts are large (0.5–1.0 μm²) and rugged (brackets), and the clefts are variable in width (15–25 nm). Presynaptic and postsynaptic membranes are hardly densified, and filamentous material is seen at intermittent spots. A and C are from radial sections stained with tannic acid; B andD are from tangential sections stained with ferricyanide.