Influences of cones upon chromatic- and luminosity-type horizontal cells in pikeperch retinas.

1. The spectral sensitivity and spatial organization of cones and horizontal cells have been analysed by intracellular recording in pikeperch retinas. 2. The vast majority of cone recordings were obtained from orange-sensitive cones. They have an action spectrum which peaks at about 605 nm. Recordings from several green-sensitive cones have also been obtained. 3. The results of action spectrum measurements and spectral screening tests indicate that the vast majority of luminosity-type horizontal cells receive predominant input from the orange-sensitive cones. 4. Chromatic-type horizontal cells were recorded at more proximal levels of the retina than luminosity-type cells and were the classic red-depolarizing, green hyperpolarizing (R/G) type. 5. The action spectra of the depolarizing and hyperpolarizing responses of chromatic horizontal cells peak at about 650 and 530 nm, respectively. When the depolarizing mechanism is selectively depressed by a red background field, the action spectrum of the hyperpolarizing mechanism shows an enhanced sensitivity, peaks at 530--540 nm, and may approximate the action spectrum of the green-sensitive cones. 6. Small red fields evoke depolarizing responses from chromatic-type horizontal cells but do not seem to significantly activate the depolarizing surround mechanism of cones. 7. These and other results suggest that the colour-opponent properties of the chromatic-type horizontal cells are not fundamentally dependent upon feed-back to cones but rather originate from antagonistic interactions generated in post-receptor networks.