Figure 6. Tracer coupling between rabbit rod and cone photoreceptor cells varies with the time of day and D₂ receptor activity.

A-E, Typical examples of photoreceptor cell tracer coupling obtained under dark-adapted conditions during the day (A), night (B), and day in the presence of spiperone (10 µM) (C), night in the presence of quinpirole (1 µM) (D), and day in the presence of SCH23390 (10 µM) (E). Shown are confocal images of whole-mount rabbit retinas taken parallel to the retinal surface at the level of the photoreceptor inner segments near the cut (Ai-Ei) and detailed perpendicular views at higher magnification of the 3D reconstruction of the labeled photoreceptor cells (Aii-Eii). The micrographs in Aii-Eii show labeled photoreceptor cells in images that range along the horizontal axis from the cuts (leftmost edge of the micrographs) to 50 µm from the cuts (rightmost edge). In addition, at the bottom of the micrographs cone pedicles are visible in Aii, Dii and Eii, and horizontal cells/bipolar cells are indicated (asterisks) in Bii and Cii proximal to the photoreceptors. Large vertical arrows indicate the location of the cuts in Ai-Ei. Some cones (small arrows) and rods (arrowheads) are indicated in Aii-Eii. Rod cell bodies are located in the innermost half of the outer nuclear layer, whereas cone cell bodies are typically located in the outermost half of the outer nuclear layer [49]. Scale bar = 50 µm (Ai-Ei); 20 µm (Aii-Eii). F, Averaged normalized fluorescence in the photoreceptor cell layer as a function of the distance from the cut under dark-adapted conditions during the day (open circles; n = 6), night (filled circles; n = 4), and during the day in the presence of spiperone (open diamonds; n = 4) or SCH23390 (open squares; n = 2), and night in the presence of quinpirole (filled diamonds; n = 4). Curves generated from the non-linear analysis of the data during the day (grey curve) and night (black curve) are also shown. Data points represent averaged data from n experiments (1 retina/condition/experiment) ± SEM.