Fig. 2. Developmental profile of TrkB staining. Two different antibodies, a pan-TrkB (A–D,I, J; raised against the extracellular domain of TrkB) and a TrkB kinase antibody (E–H; raised against the kinase domain of TrkB), were compared in their staining pattern. The two antibodies gave basically identical staining, arguing that all cells either express the full-length form or both the full-length and the truncated forms of TrkB. TrkB expression follows the maturation of the retina from inner (A,E) to outer retina (D,H). Note the staining of horizontal cells by P6 (B, F, arrows), the radial Müller glia cells (with their micrivillous processes forming a layer at the level of the inner segments of the photoreceptors) at all stages (e.g., C, G, large arrowheads), and the strata in the inner plexiform layer (D,small arrowheads). Whole-mounts of RPE demonstrate labeling of TrkB receptors on the lateral surfaces of the RPE cells (I, J) and in clusters on the apical surface of the cells (I,J,arrows). HC, Horizontal cells; IS, inner segments; PR,photoreceptors; RGC, retinal ganglion cells; other abbreviations are defined in Results.