Separation and light adaptation of rod and cone signals in the retina of the goldfish.

The aspartate-isolated fast P III response was used to monitor the responses of goldfish photoreceptors at varying intensities of steady background illumination. When the retina contained the normal complement of rods and cones, light adaptation consisted of response compression, a shift of the response curve to more intense stimuli (cellular adaptation), and responses to decrements as well as increments of light. Rod and cone contributions to the fast P III response were separated by taking advantage of photomechanical movements of the photoreceptors to produce "all-rod" and "all-cone" retinae. Rods employ response compression as their primary adaptation mechanism. Rods show little cellular adaptation or responses to decremental flashes. However, cones do not show response compression, but continue to respond at bright backgrounds due to cellular adaptation.