Fig. 7.

Serial connections significantly suppress BC L-IPSCs and create a maximum response at intermediate light stimuli sizes. A suppression index (SI, A) and the light stimulus size that elicited the maximum L-IPSC (B) were calculated from the ARFs of each recorded BC in control and bicuculline. A: in control conditions, the SI was significantly >1 for all BC types (rod, n = 19; P < 0.0001; on, n = 14, P < 0.01; off, n = 9, P < 0.01), showing significant suppression of large-sized light stimuli, while in bicuculline, the SI = 1, showing no suppression (rod, n = 11, P = 0.8; on, n = 5, P = 1; off, n = 5, P = 0.3). B: similarly, in control, the size of light stimulus eliciting the maximal L-IPSC was significantly less than the maximum light stimulus size (825 μm) in all BC types (rod, P < 0.0001; on, P < 0.0001; off, P < 0.01). In bicuculline, the light stimulus size that elicited the maximal L-IPSC was not different from 825 μm, the largest size of light stimulus used (rod, P = 0.2; on, P = 1; off, P = 0.2). Thus when serial connections were blocked by bicuculline, the suppression of L-IPSCs by large light stimuli was not observed.