The feedforward component in depolarizing red responses of R/G horizontal cells in carp retina.

Light responses of R/G chromaticity-type horizontal cells (R/G HCs) and luminosity-type horizontal cells (LHCs) were intracellularly recorded in isolated superfused carp retina, and the response dynamics analyzed. The results revealed that (1) No significant difference in delay was detected between R/G HC red and green responses; (2) The rising speed was quicker for R/G HC depolarizing red responses compared to that of its hyperpolarizing green responses; and (3) Dynamic characteristics of R/G HC red responses and its changes caused by green background illumination did not follow that of LHC red response. All these results suggest that the depolarizing response of the R/G HCs cannot be entirely mediated by the negative feedback pathway from LHCs onto cones. A direct inhibitory input from red cones to R/G HCs may exist.