Objective To explore the connection between the melanin content of retinal pigment epithelial (RPE) cells and the function of photoreceptors, and the function of melanin on retinal light damage. Methods Agematched old dopachrome tautomerase knockout (DCT-/-) mice and wildtype mice were collected as the DCT-/- group and wildtype group, with 20 mice in each group. Baseline electroretinograms (ERG) in accordance with the international standards for the clinical electrophysiology were performed on all the mice, and the max ERG was recorded. Two mice were randomly selected in each group and were executed，and the removal eyeballs were as the control. The remaining 18 mice in each group were exposed to cold fluorescent light with the quantity of electricity of 20 W for 36 hours with a circle of 12 hours light12 hours dark12 hours light, which was repeated continuously for three times. The light intensity was (5000plusmn;356) lx. Six days after the light illumination, ERG were performed again and the results were recorded. Cervical dislocation methods were used to executed 2 mice which were chosen randomly in each group, and the eyeballs were removed. The tissue sections were observed under the optical and electron microscope.Results The results of ERG showed that the amplitude of a and b wave was lower in DCT-/- group than that in wildtype group before and after light injury （a wave before light injury: t=-7.13，Plt;0.01；b wave before light injury: t=-4.414，Plt;0.01；a wave after light injury: t=-10.162，Plt;0.01；b waveafter light injury: t=-6.772，Plt;0.01）. The decrease of amplitude of a and b wave was much obvious in DCT-/- group than that in wildtype group （a wave:t=4.975,Plt;0.01；b wave:t=2.908,Plt;0.01）. After the light injury, retinal edema and thinning were found in DCT-/- group which wasobvious than that in wildtype group; the photoreceptor layers and melanin were more seriously affected in DCT-/- group than that in wild-type group.Conclusions After the light illumination, the melanin of RPE cells reduces and the function of photoreceptors decreases, which suggests that melanin may play an protective role in the light injury.
Objective To investigate the relationship between exposure intensity and illumination time of blue light and replicative senescence of rat retinal pigment epithelial （RPE） cells.Methods Thirtysix 12-14 weeks Wistar rats were kept in the cage with a bluelight bulb ［(450plusmn;10) nm］, and were randomly divided into four groups (no light，nature light，500 lx light and 1000 lx light illumination), each has nine rats. The rats in each group were further divided into three subgroups according to illumination time (one month，two months or three months). Eyeballs were collected after intraperitoneal injection of 10% chloral hydrate. The right eye of each rat was embedded in paraffin and sectioned for hematoxylineosin (HE) staining, while frozen sections of the left eye were stained for the senescence-associated beta;-galactosidase (SA-beta;-Gal). The data were analyzed by SPSS11.5 statistical software.Results The amounts of SA-beta;-Gal positive RPE cells were significantly different between all groups under the same illumination time 17 (P＝0.000）, and between all subgroups of different illumination time with same exposure intensity （P＜0.01）except for the control group (no light). Conclusion Bluelight can induce replicative senescence in rat RPE cells in an intensity and timedependent manner.