Effects of light and darkness on cell deaths in damaged retinal ganglion cells of the carp retina

Effects of light and darkness on the apoptosis of retinal ganglion cells (R GCs) in young carp were measured by TUNEL method after transection of the o ptic nerve. Following the operation, the fish were kept under one of four r egimens; constant darkness (DD), constant light (LL), 12 hr light and 12 hr dark (LD) and 3 hr of flickering light followed by 21 hr in the dark (FL). On day 3, the highest ratio of apoptotic RGCs was seen under conditions of DD, followed by LL, LD, and FL. On day 6, the percentages of apoptotic RGC s were lower under every experimental condition than what they had been ear lier on day 3, but the same ranking order was maintained. Immunohistochemic ally it could be shown that phosphorylated ERKs were more intensively local ized in FL rather than DD retinas. The results suggest that illumination re gimens, and in particular cyclic diurnal light/dark changes, have an influe nce on the degree of apoptosis of damaged RGCs, and that inhibition of apop tosis is correlated with the higher expression of phosphorylated ERKs.