Light adaptation of rod and cone luminosity horizontal cells of the retina of the goldfish.

Intracellular recordings from rod horizontal cells and luminosity external horizontal cells of the goldfish retina were obtained, and the process of light adaptation induced by steady, full-field background illumination was investigated. Rod horizontal cells had remarkably steep response vs intensity (rvi) functions when dark-adapted. Background illumination reduced the sensitivity of these cells primarily due to response compression, with intense backgrounds resulting in eventual response saturation. Increment threshold functions for these cells were non-linear, and increment saturation was evident when 500-nm backgrounds exceeded 10.5 log photons s-1 cm-2. Cone luminosity cells displayed broad response operating functions when dark-adapted. Light adaptation resulted in substantial narrowing of the rvi function, as well as a shift in the operating function to greater intensities. Response compression played only a minor role in the loss of sensitivity of these cells.