RHYTHMS IN THE GOLDFISH VISUAL SYSTEM: ROD OUTER SEGMENT SHEDDING AND VISUAL SENSITIVIT

I investigated the role of circadian rhythms in goldfish visual function. Rod outer segment shedding was characterized under cyclic artifical light, natural light, and after 1, 3, or 7 days in constant light or constant darkness. A burst of rod shedding was observed after light onset in cyclic artificial light; shedding was also observed during the day in natural light but the amount of shedding was less than in artificial light. Shedding was abolished in all of the constant conditions suggesting that a circadian oscillator is not directly responsible for the rhythm of shedding observed in cyclic light. The rod outer segments became progressively longer in both constant light and constant dark conditions; however they were longest in constant light. Shedding could be induced in animals exposed to constant light by dark-adapting them for 2 hours and then re-exposing them to light.;Behavioral absolute visual sensitivity was measured in goldfish before and after exposure to constant light for 7 days. Goldfish were more sensitive (.29 log unit) to rod stimuli after the exposure. The increase in sensitivity could in part be accounted for by the increase in rod outer segment length observed in the previous experiment (.20 log unit). In another experiment, absolute visual sensitivity was found to vary over time of day in animals maintained in constant darkness.;Rhythms within the retina were compared to other rhythms exhibited by goldfish. Locomotor activity was measured in individual fish in cyclic light and constant conditions. As with rod shedding most fish showed a rhythm in locomotor activity in cyclic light and no rhythm in constant conditions. Retinal uptake of ('3)H-melatonin was also examined because this compound has been shown to be associated with rod shedding, sensitivity, and locomotor activity. More ('3)H-melatonin was retained in dark-adapted retinae than light-adapted retinae, regardless of time of day.