Figure 2. Spatially local gain control at the rod bipolar-to-AII amacrine synapse.
(A–D) Paired recordings between a current-clamped presynaptic rod bipolar cell and voltage-clamped postsynaptic AII amacrine cell. (A) Rod bipolar voltage response to a current pulse of 30 pA for 50 ms. (B and C) Postsynaptic responses of an AII amacrine cell to a presynaptic current pulse in darkness (B) and on a background producing 1 Rh*/rod/s (C). Thick traces are the average of 5–10 responses. (D) Averages in darkness (black) and on background light (gray) overlaid. (E) Gain (G) in the presence of background light normalized to the gain in darkness (Gdark) for synaptic pulse and flash responses in AII amacrine cells. Closed (open) circles are individual postsynaptic responses in AII amacrine cells for presynaptic current-clamped (voltage-clamped) rod bipolar cells and squares are mean ± s.e.m. (current clamp: G/Gdark of 0.54 ± 0.03 for pulse; 0.39 ± 0.03 for flash; mean ± s.e.m.; n = 18; voltage clamp: G/Gdark of 0.91 ± 0.03 for pulse; 0.36 ± 0.03 for flash; mean ± s.e.m.; n = 17). Postsynaptic responses to voltage-clamp pulses were significantly different from those to current-clamp pulses (paired t-test; p < 0.0001) and from flash responses (p < 0.0001). (F–I) Paired recordings between a voltage-clamped presynaptic rod bipolar cell and voltage-clamped postsynaptic AII amacrine cell. (F) Rod bipolar current response to a voltage pulse of 30 mV for 50 ms. (G and H) Postsynaptic AII amacrine responses to the presynaptic voltage pulse in darkness (G) and on a background producing 1 Rh*/rod/s (H). Thick traces are the average of 5–10 responses. (I) Averages in darkness (black) and on background light (gray) overlaid. Averages begin before time 0 due to digital filtering.