Ultraviolet Light Damage and Reversal by Retinoic Acid in Juvenile Goldfish Retina
Because their spectral sensitivity shows that ultraviolet [UV] light reaches the retina, 1 we utilized juvenile goldfish [Carassius auratus] to study light damage induced by 300–400nm light at about 30μWcm-2. Electron microscopy [EM] and the electroretinogram [ERG] were used to assay retinal health. Cone ellipsoids in the vicinity of mitochondria were tortuous and swollen at 3 days of such near-UV treatment. Double cones showed some outer segment damage. Curiously, at 6 days, some mitochondria were displaced toward the external limiting membrane in double cones. By 12 days, the double cone outer segments were nearly gone, and the mitochondrial displacement extended to single cones [including UV cones]. Inner segments were filled with a smooth reticulum. Rods were normal. Although there was ultimately [by 32 days] a preferential loss of UV visual sensitivity, at 12 days a UV sensitivity peak remained which could be isolated by chromatic adaptation, suggesting that UV cones continued to function. Widespread cone damage by UV light suggests a mechanism independent of visual pigment absorbance, though the delayed loss of UV sensitivity in UV cones may be mediated through their UV rhodopsin. Retinoic acid had been implicated in protection of photoreceptors from light damage, retinal development, and gene transcription. All-trans retinoic acid [1 μM] was added to the aquarium. Treatment of 3-day-UV fish with retinoic acid for 5hr and of 12-day-UV fish for 7hr reversed many of the signs of UV damage.
KeywordsRetinoic Acid Outer Segment Visual Pigment Double Cone Single Cone
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