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Christophe P Ribelayga, Nange Jin, Zhijing Zhang, Eduardo L Silveyra; A Circadian Clock Controls the Transmission of Scotopic Signals from the Rod to Rod Bipolar Cell in the Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4139.
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© ARVO (1962-2015); The Authors (2016-present)
Under dim scotopic conditions, vision relies on the detection of single photons by rods and the synaptic transfer of the rod single-photon responses to rod bipolar cells (RBCs). It has been proposed that a threshold non-linearity in RBCs rejects continuous noise from rods while preserving signals that exceed a criterion amplitude. We recently reported that electrical coupling between rods is controlled by a circadian clock so that coupling is weak during the day and much stronger at night. An increase in rod electrical coupling at night is expected to reduce the amplitude of the rod single-photon responses and therefore reduce signaling in the rod pathway, unless other mechanisms are at play. Here, we sought to determine whether performance of the RBC changes between day and night.
We patch-clamped RBCs in CBA/Ca mouse retinal slices and recorded their light-evoked voltage responses at different times in the circadian cycle.
During the subjective day, we found strong non-linearity in the light responses of RBCs. As expected, this high non-linearity translated into a high signal-to-noise ratio (SNR) of the single-photon responses in RBCs (4.16). In contrast, during subjective night, the average voltage response-intensity function appeared more linear compared to the daytime, as evidenced by a decrease in the Hill coefficient (from 1.45 to 1.00). We also found that the amplitude of the single-photon responses were larger (from 1.6 mV to 2.6 mV) and the SNR was lower (from 4.16 to 2.26) in RBCs at nighttime. Whereas the amplitude of the rod single-photon voltage-response decreases between subjective day and subjective night (from 2.5 mV to 1 mV), the amplitude of the single-photon response in RBCs increases; the data indicate that the voltage gain of the rod-to-RBC synapse increases at nighttime by a factor of 4.
Our data suggest that rod-to-RBC signaling is controlled by a circadian clock on a daily basis. Specifically, the rod-to-RBC synapse operates at low gain during the subjective day and high gain at night. The nighttime increase in gain may represent a compromise of the decreasing false negative rate in order to cope with the small amplitude of the rod single-photon responses and increasing false positive rate.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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