Light response kinetics of rabbit A-type horizontal cells varies with the time of day and D₂ receptor activity.

A, Representative examples of A-type horizontal cell responses to a light stimulus flashed (500 ms) at intensity −2 log Io recorded during the subjective day (gray trace) and subjective night (black trace). The amplitude of each response has been normalized relative to its peak for better comparison of the traces. Scale bar: 1 s. B, Average latency, C, time-to-peak, and D, total duration of the hyperpolarizing portion of A-type horizontal cell light responses recorded under dark-adapted conditions during the night and subjective night (filled circles, solid line; n = 7), day and subjective day (open circles, solid line; n = 14), and day in the presence of spiperone (open diamonds; n = 9) or SCH23390 (open squares; n = 8), and night in the presence of quinpirole (filled diamonds; n = 8). Two-way ANOVA analysis revealed both intensity and condition effects for each response property measured. See Materials and Methods for definitions of response measures. Data points represent averaged data from n cells (1 cell/retina) ± SEM.