The dark adaptation behaviors of rod-driven and cone-driven horizontal cells were exam-ined by analyzing their light responses recorded intracellularly in the intact, immobilizedcarp, and compared with that of the electroretinographic b--wave recorded simultaneously.Like the b--wave, the light responsiveness of rod horizontal cells increased gradually withtime in the dark and attained a steady level at 60 min. On the other hand, cone horizontalcells initially increased in light responsiveness in the first 10 min, but thereafter decreasedsteadily so that the response amplitudes of these cells to bright light flashes were only 3--5 mV.The results suggest that cone horizontal cells are strongly suppressed in prolonged darkness.
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