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Christophe Ribelayga, Nange Jin; Circadian clock and dopamine control of rod photoreceptor electrical coupling in mouse retina. Journal of Vision 2013;13(15):P7. doi: https://doi.org/10.1167/13.15.42.
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Rod photoreceptors play a critical role for vision under dim light by providing the reliable detection and transmission of single photons. Phototransduction current in the rod outer segment and photocurrent from electrically coupled neighboring rods are central processes that shape the rod photovoltage in vertebrates in general. However, in mammals, the regulation and contribution of electrical coupling to the rod light response have remained unclear and controversial. In addition, the limited data available reflects the experimental difficulty to electrically access the inside of the mammalian photoreceptor because of its small size.
We have developed a patch-clamp method to record the light-evoked responses of single photoreceptors in the isolated intact neural mouse retina maintained by superfusion. We found that under dark-adapted conditions, during both daytime and nighttime, rod voltage responses to dim flashes of light were consistent with the quantal nature of light and the rod ability to detect single photons. While the rod light responses were slower and smaller in amplitude at night, they were more reliable as compared to the day, indicating an increase in rod electrical coupling at night. Tracer coupling measurements and pharmacological manipulations provided further evidence that rods were electrically isolated during the day and coupled at night, and that the temporal variation in rod coupling required dopamine and D2-like receptors. We propose that the daily activation of D2-like receptors, driven by the circadian rhythm in retinal dopamine, in turn controls electrical coupling of rods.
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