Effects of 2-amino-4-phosphonobutyrat (40–80 µM APB) on neuronal activity of single units.

Responses of 3 units (mean and standard deviation of 10 measurements) to flashed and moving ON (A) and OFF (B) visual stimuli before (control) and after intravitreous drug injection (APB; intravitreous concentration 40–80 µM). Ordinate: neuronal activity in spikes per second, abscissa: experimental conditions. APB blocks responses to all ON stimuli but spares the OFF flash response and the responses to the moving dark edge, albeit moderately decreased. Grey boxes: flash responses; black boxes: responses to moving edges in preferred direction; white boxes: responses in non-preferred direction.