Immunofluorescent images and analysis of cell death by TUNEL assay (green); the cell nuclei are counterstained with DAPI (blue) in non-cultured control retinas (A) and retinas cultured or co-cultured for 3 (B, C) or 5 days in vitro (D, E). Cell death in the outer nuclear layer (ONL) and in the inner nuclear layer (INL) increased over time in the cultured (indicated by arrows in B and D) and co-cultured (indicated by arrows in C and E) retinas when compared to the non-cultured control retinas (A). After 3 days of co-culture with ARPE cells (C, F), cell death was decreased in the retinal specimens when compared to the control retinas (B, F) after 3 days of culture. Cultured retinas retained normal layering post-culture (B–E), shown by separate nuclear layers in the DAPI-stained sections: the outer nuclear layer (ONL), inner nuclear layer (INL), and inner ganglion cell layer (GCL). After culture, the specimens showed holes and injuries, indicated by (*) in the retinal tissue. Occasionally, some TUNEL-labeled ARPE cells were found in the co-culture setup (arrow in ARPE layer in C). Data are expressed as means ± SEM; *P < 0.05; n = 4; scale bars, 20 μM.