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C Ribelayga, SC Mangel; A Circadian Clock In The Vertebrate Retina Regulates Dopamine Release . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1361.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Although a variety of cellular phenomena in the retina exhibit circadian rhythms, only melatonin release has been shown to be regulated by a clock present in the retina itself. We therefore sought to determine whether a retinal clock regulates dopamine (DA) release. Methods: Goldfish retinas were isolated under infrared conditions and cultured for up to 56 hours at 20C in constant darkness in a Ringer-based culture medium with supplements. Culture medium was changed every 4h. DA was purified and concentrated from the medium using aluminum extraction. Reversed-phase HPLC with electrochemical detection was used to determine the amount of released DA. DA content was determined in retinal homogenates to express the amount of released DA as a function of the total amount of available DA. Drugs that affect DA metabolism were not used. Results: In our culture conditions, DA released from isolated retinas accumulated in the medium and was measurable following extraction at all times of the circadian cycle. The retinas were still viable at the end of the experiment since incubation in a high concentration of potassium stimulated DA release. The amount of DA in the medium fluctuated according to the time of day. The highest levels of DA were observed during the subjective day (first time point of the culture CT 10: 64.45 ± 0.85 pg/retina/4h (4.27 ± 0.60% of total DA); CT 6 on the first subjective day: 57.49 ± 3.27 pg/retina/4h (3.77 ± 0.41% of total DA); CT 6 on the second subjective day: 59.27 ± 4.23 pg/retina/4h (4.07 ± 0.79% of total DA); SEM, n=4), and the lowest DA levels during the subjective night (CT 18 on the first subjective night: 42.95 ± 9.16 pg/retina/4h (2.71 ± 0.46% of total DA); CT 18 on the second subjective night: 39.44 ± 5.14 pg/retina/4h (2.61 ± 0.45% of total DA); SEM, n=4; p<0.05 compared to the first time point of culture). These day/night variations in DA release persisted during the 3 day-culture with a period of approximately 24h. Conclusion: Our work demonstrates for the first time that in the vertebrate retina, DA release is under the control of a retinal clock so that DA release increases during the subjective day and decreases during the subjective night.
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