Manganese and copper-zinc superoxide dismutases in the developing rat retina

To determine whether superoxide dismutases (SODs) may be connected with cellular differentiation in the retina, we studied these enzymes by immunolocalization and immunochemical quantitative analysis in developing rat retinas. Four days after birth, manganese superoxide dismutase (Mn-SOD) and copper-zinc superoxide dismutase (CuZn-SOD) immunoreactivities were observed in the neural retina but not in immature neuroblasts. In 9-day-old rats, Mn-SOD immunoreactivity was located in the ganglion cell layer, inner plexiform layer, some cells of the inner nuclear layer, outer plexiform layer, and photoreceptor inner segments differentiated from immature neuroblasts. CuZn-SOD immunoreactivity was found in the same sites except the photoreceptor inner segments. The immunohistochemical staining in 9-day-old rat retinas was the same as in adult retinas. Our quantitative analysis showed increased SODs when retinal cell differentiation ceased. Our results suggest that the concentration of SODs in retinal neuroblasts is too low that immunoreactivity of SODs cannot be visualized. When the differentiation of retinal neuroblasts progresses, SODs appear to be increased in mature retinal cells to protect them from oxidative stress induced by light exposure when the eyes are open.