Figure 2. Immunohistochemical detection of rhythmic phagocytosis in short wavelength sensitive (S)-cones of young adult Nrl^−/− and wild-type mice. A and B: These two sections were taken from animals killed under light-dark conditions at, respectively, hour 1 and hour 10 of zeitgeber time. C and D: These two sections were taken from animals killed under total darkness conditions at, respectively, hour 1 and hour 10 circadian time.. Sections immunolabeled with S-cone opsin antibody show the continuous row of cone outer segments across the section, and the presence of numerous immunoreactive inclusions (phagosomes=Ph) within the retinal pigment epithelium (RPE; short arrows) at ZT1 and CT1, but not at ZT10 and CT10. E: S-cone opsin immunostaining of wild-type mouse retina (ZT6) shows the presence of occasional labeled COS (long arrows). RPE, retinal pigment epithelium (the approximate level of the basal surface of the RPE) is shown by a dashed line in panels A-D. Scale bar in E represents 10 μm for all panels.