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Nange Jin, Christophe Ribelayga; Circadian Clock Control of Rod Photoreceptor Electrical Coupling in the Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):405.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal processing of visual information varies with the time of day by light/dark adaptive mechanisms and circadian clocks intrinsic to the retina. While it has long been known that rods primarily operate under dim light levels and cones under bright light levels, little is known about how photoreceptors respond to light under circadian conditions. Here we performed patch clamp recordings of the light responses of mouse rod photoreceptors at different times in a circadian cycle.
Experiments were conducted in the CBA/CaJ mouse, in which a circadian rhythm of dopamine release occurs in retinal tissue with peak and trough values during the subjective day (SD) and subjective night (SN), respectively. Perforated patch clamp recordings from single rod inner segments were performed in dark-adapted isolated intact neural mouse retinas maintained by superfusion. Responses to 20-ms dim (scotopic) full-field 500 nm light stimuli were recorded. Recorded rods were labeled by iontophoresis of the biotinylated tracer Neurobiotin, and cones were labeled with Dylight649-conjugated peanut agglutinin.
During SD and SN, rod responses to dim flashes of light were consistent with the quantal nature of light and the rods ability to detect single photons. However, the rod light responses were slower and smaller in amplitude, yet more reliable during SN compared to SD, indicating an increase in rod electrical coupling at night. Following iontophoresis of Neurobiotin into single rods, tracer was restricted to the recorded cell during SD but was observed in many neighboring rods and cones during SN. Application of the dopamine D2-like receptor antagonist spiperone during SD mimicked the nighttime state. Conversely, application of the dopamine D2-like receptor agonist quinpirole during SN mimicked the daytime state. Finally, application of the gap junction blocker meclofenamic acid had limited effects on the rod light response variability and amplitude during SD but increased the variability of the rod responses to dim light stimuli and the amplitude of the light responses during SN or during SD in the presence of spiperone.
Our data provide electrophysiological and tracer coupling evidence that a circadian clock in the mammalian retina uses dopamine and D2 receptor activation to regulate rod electrical coupling, therefore, modulating the light responses of rods.
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