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S. C. Mangel; A Circadian Clock Controls Rod and Cone Input to Rabbit Retinal Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3865.
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© ARVO (1962-2015); The Authors (2016-present)
Circadian and diurnal rhythms of visual sensitivity and responsivity have been found in many vertebrate species, including rabbit and human (Barlow, 2001). A circadian clock in the mammalian retina regulates dopamine, melatonin production and release, and pH (Dmitriev and Mangel, 2001; Green and Besharse, 2004; Iuvone et al., 2005). Recent work has also shown that the circadian clock in the fish retina regulates rod and cone input to cone horizontal cells by controlling rod-cone electrical coupling, so that cone input dominates in the day and rod input dominates at night (Wang and Mangel, 1996; Ribelayga et al., 2004; Ribelayga et al., 2007, ARVO). Because a circadian clock regulates rod and cone input to rabbit horizontal cells (Ribelayga and Mangel, 2005, ARVO), we investigated whether a clock regulates the light responses of rabbit ganglion cells.
Rabbits were entrained to a 12-hr light/12-hr dark cycle before each experiment. Surgery was performed under infrared illumination. Rabbit eyecups were superfused with Ames medium. Standard extracellular recording techniques were used to record ganglion cell light responses to dim achromatic light stimuli during the subjective day and night. Background illumination was maintained in the low scotopic range during electrical recording.
Light response thresholds for ON- and OFF-transient and sustained ganglion cells were approximately three orders of magnitude lower during the subjective night compared to the subjective day. Ganglion cells responded to light in the low scotopic range at night. In both the subjective day and night, repetitive bright light stimulation increased light response thresholds to a level one order of magnitude greater than that of cells recorded during the subjective day. In both the subjective day and night, ganglion cell light responses exhibited a receptive field center, but not a receptive field surround. Ganglion cell spontaneous activity was lower during the subjective night than in the day. In addition, at night some ganglion cells exhibited spontaneous rhythmic bursting. These cells had higher light response thresholds than non-bursting cells. Repetitive bright light stimulation abolished the bursting activity by increasing the spontaneous activity to a level greater than the peak of the bursting.
These findings suggest that a circadian clock regulates the light responses of rabbit retinal ganglion cells so that cone input dominates during the day and rod input dominates at night. The primary function of the circadian clock in the mammalian retina may be the regulation of rod and cone pathways.
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