Figure 4. AII amacrine cell responses to Michelson contrast depend on the rod → rod bipolar cell pathway.

(A1) Responses to contrast modulation (100% contrast; 1 Hz) at background = 2 R*/rod/s. Responses in control conditions and in the presence of DNQX (100 μM) are shown. At right: averaged responses to one cycle. Same conventions as in Figure 3A. V_hold = −70 mV (10 kHz sampling; 2 kHz Bessell filtering). (A2) Same format and cell shown in A1 at a higher mean background. (B1) Average On and Off integrated responses in AIIs (n = 4; 0.3-mm diameter spot), normalized to the Off response at the 128 R*/rod/s background and multiplied by −1 to generate the same sign as in Figure 3B. OFF cell responses from Figure 3B2 are shown (shifted rightward) for comparison. Error bars: ±SEM across cells. (B2) Same format as B1 for AII cells and OFF ganglion cells recorded in the presence of DNQX (n = 4). (C) Baseline currents measured in AII cells (n = 4) relative to the baseline current measured under control conditions at the 2 R*/rod/s background. Error bars: ±SEM across cells. (D) Variance measured during the baseline currents shown in C. (E) Average cycle responses to contrast modulation at two mean luminances in an example AII cell measured under control conditions and in the presence of DNQX (100 μM) and DNQX + D-AP5 (100 μM). (F) Light-evoked currents are largely excitatory. Left: averaged responses to contrast modulation at the 256 R*/rod/s background were largely unaffected by blockade of postsynaptic GABA_A (GABAzine, 20 μM) and GlyRs (strychnine, 2 μM; purple). Adding DNQX (100 μM) attenuated the response and made it biphasic (as in A2). Right: depolarizing the AII to E_cation reduced current amplitudes without affecting waveform, indicating that currents are largely excitatory and carried by cations. (G) Summary of data illustrated in (F) for n = 4 recorded AIIs. Currents were averaged over the windows illustrated by green and red bars in (F).