Figure 9.

Control experiments to confirm that the effect of TPMPA on the rectification of OFF ganglion cells depends on the ON bipolar cell. A, Excitatory currents from OFF ganglion cell in control conditions, in TPMPA, and then with the ON bipolar cell hyperpolarized by adding l-AP4 to TPMPA. Some current deflections return to the baseline when TPMPA is applied, but fail to do so when l-AP4 is added, consistent with an increase, and then a decrease in rectification (arrows). B, TPMPA increased gain in all cells, but adding l-AP4 to TPMPA decreased gain (4 G5 cells; the dashed lines connect the same cells under different conditions). C, TPMPA made the static nonlinearity more curved and thus increased rectification, but adding l-AP4 to TPMPA straightened the static nonlinearity and thus decreased rectification. D, Effect of drugs on rectification. Most cells are above the diagonal for TPMPA but go below it when l-AP4 is added to TPMPA, suggesting that l-AP4 blocked the effect of TPMPA.