Figure 4. Light-induced signal transmission to the inner retina. After complete dark adaptation, animals and organ cultures were exposed to 1 Hz stroboscopic illumination for 2 h. This procedure examines whether the inner retina can respond to a sustained signal from the photoreceptors. A: C-fos expression was induced by stroboscopic illumination in cells in the inner nuclear layer and the retinal ganglion cell layer of the intact animal. D: In organ cultures, c-fos expression could also be demonstrated using this paradigm. Images are representative examples from organ cultures derived from three different litters. For each image, a corresponding bright-field image is provided for orientation (B and C). In the absence of stroboscopic illumination, no c-fos immunoreactivity was observed in vivo (E) or in vitro (F). G: A no-primary antibody control is provided for nonspecific staining of the secondary antibody. Abbreviations: GCL, ganglion cell layer; INL, inner nuclear layer; IPL, inner plexiform layer; IS, inner segments; ONL, outer nuclear layer; OPL, outer plexiform layer; OS, outer segments. The scale bar represents 20 μm.