Repetitive red flashes increased the R/G horizontal cells' red response amplitude and induced a hyperpolarization of the cells' dark membrane potential. These phenomena were eliminated in 6-OHDA pretreated retinas and restored by exogenous dopamine, which suggests the involvement of dopamine receptor activity changes instead of dopamine release changes. Furthermore, the phenomena persisted on D 1 receptor antagonist (SKF-83566) application, whereas they diminished on D 2 receptor antagonist (eticlopride) application, indicating that the mechanism is related to a D 2 receptor, possibly located on photoreceptors.