Light adaptation in luminosity horizontal cells in the turtle retina. Role of cellular coupling.

Intracellular recordings were made from L-type horizontal cells in the retina of the turtle Clemmys caspica. The test flashes covered a retinal area smaller than the receptive field of the impaled cells. Increment responses were compared between two states of light adaptation that were equal in intensity but differed in spatial pattern. The peak amplitude of the response to a dim test flash was larger when measured during large-field background compared to the one obtained during small-field one. It is suggested that this phenomenon of surround enhancement is due to the cellular coupling between neighboring horizontal cells.