A circadian clock regulates rod and cone input to fish retinal cone horizontal cells.

May 14, 1996Proceedings of the National Academy of Sciences of the United States of America

A daily biological clock controls rod and cone signals to cone horizontal cells in fish retina

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Abstract

Light responses of cone horizontal cells in goldfish are regulated by a circadian clock, showing significant variation based on the time of day.

After prolonged darkness at night, cone horizontal cells exhibit light responses similar to rod horizontal cells.
Responses of cone horizontal cells to bright light are greater during the subjective day compared to the subjective night.
The spectral sensitivity of cone horizontal cells during the subjective night closely aligns with that of rod horizontal cells.
A prior reversal of the light/dark cycle can reverse the 24-hour rhythm of cone horizontal cell responses.
Light responses differ significantly between rod and cone horizontal cells after light sensitization in both day and night conditions.

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In the vertebrate retina, the light responses of post-receptor neurons depend on the ambient or background illumination. Using intracellular recording, we have found that a circadian clock regulates the light responses of dark-adapted fish cone horizontal cells. Goldfish were maintained on a 12-hr light/12-hr dark cycle. At different times of the day or night, retinas were superfused in darkness for 90 min ("prolonged darkness"), following which horizontal cells were impaled without the aid of any light flashes. In some of the experiments, fish were kept in constant darkness for 3-48 hr prior to surgery. After prolonged darkness during the night, but not during the day, the light responses of L-type cone horizontal cells resembled those of rod horizontal cells with respect to threshold, waveform, intensity-response functions, and spectral sensitivity. Following light sensitization during the night and day, the light responses of rod and cone horizontal cells were clearly different with respect to threshold, waveform, intensity-response functions, and spectral sensitivity. Under conditions of constant darkness for two full light/dark cycles, average responses of cone horizontal cells to a bright light stimulus during the subjective day were greater than during the subjective night. Prior reversal of the light/dark cycle reversed the 24-hr rhythm of cone horizontal cell responses to bright lights. In addition, following one full cycle of constant darkness, average cone horizontal cell spectral sensitivity during the subjective night closely matched that of rod horizontal cells, whereas average cone horizontal cell spectral sensitivity during the subjective day was similar to that of red (625 nm) cones. These results indicate that the effects of dark adaptation depend on the time of day and are regulated by a circadian clock so that cone input to cone horizontal cells predominates in the day and rod input predominates in the night.

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A circadian clock regulates rod and cone input to fish retinal cone horizontal cells.

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