Control of retinal sensitivity. 3. Lateral interactions at the inner plexiform layer.

Both the "on" and the "on-off" ganglion cells in the mudpuppy retina generate graded responses over a narrow range of log test intensities. Sustained full field or surround backgrounds change the range of center log test intensities that elicits the graded response for both cell types. The on-off, but not the on ganglion cells are further affected by moving or flashing surround backgrounds. These cells are hyperpolarized, threshold is elevated, and the entire graded range of response is elicited by a higher range of log center test intensities. Depolarizing activity is elicited in amacrine cells by moving backgrounds that affect the on-off ganglion cells, but bipolar activity is unaffected. These results suggest that the amacrine cells at the inner plexiform layer mediate a third stage of sensitivity control in the retina, increasing threshold for response to change specifically in the on-off ganglion cells.