Figure 8.

Gnb3-null rod bipolar dendrites are not maintained in the invagination of the rod terminal. A, B, Electron micrographs of rod terminals (RT). In WT retina, numerous profiles of rod terminals (outlined by dotted lines) are seen with one or two rod bipolar dendrites (b) postsynaptic to the rod's synaptic ribbon (r). In Gnb3-null (KO) retina, bipolar dendrites are usually smaller and are rarely observed. Horizontal cell processes (h) are seen with the same frequency in WT and KO. C, Bar graph describes the percent of profiles in which a ribbon, at least one horizontal cell process (Horiz.), or at least one rod bipolar dendrite are observed. For each category, we show the percentage at 3 weeks (3w) and 4–7 weeks (A) for wild type (black) and Gnb3 KO (gray). The number of profiles analyzed for WT were 218 (3w; n = 2) and 395 (A; n = 3), and for Gnb3-null they were 351 (3w; n = 2) and 404 (A; n = 3). The difference between WTs and nulls at 4–7 weeks was significant (χ² test, p < 0.005). D, E, Electron micrographs of cone terminals (CT). These terminals (outlined by dotted lines) are seen in both wild-type and null retinas, but in null retinas they appear darker with a density that resembles their neighboring rod terminals. mit, Mitochondrion. Scale bar: (in E) A, B, 0.455 μm; D, E, 1 μm. F–I, ERG records at different ages in wild-type (F, G) and null (H, I) mice. To compare shapes, we averaged traces from each age group and normalized this average trace to its minimum (peak of a-wave). The numbers of records averaged for each trace were 4 (3w), 6 (4–8w), and 2 (30w) for WT and 4 (3w), 6 (4–8w), and 4 (30w) for Gnb3-null. In G and I, the time scale is expanded to show the initial oscillations. Note that in wild-type mice (G), the oscillations at 3 weeks lag behind those in older adults (gray and black arrows, respectively), while in null mice (I), they appear simultaneously (gray arrows), although they all lag behind the wild-type oscillations. Note the different time scales in G and I.