Light adaptation of red cones and L1-horizontal cells in the turtle retina: effect of the background spatial pattern.

Electrical coupling allow red cones and L1-horizontal cells to respond to light stimuli illuminating remote retinal loci. The contribution of the spatial pattern of background light to flash sensitivity of red cones and L1-horizontal cells was studied intracellularly in the turtle retina. Lateral spread of background adaptation was observed in the cones. The sensitivity of the cones was related to the steady hyperpolarization of the cells irrespective of the background's spatial pattern. Light sensitivity of L1-horizontal cells mainly depended upon the background illuminating their dendritic field. Unlike red cones, the horizontal cells responded differently to spot and annular backgrounds regardless of the steady hyperpolarization induced.