(A) Average traces and plots showing abGC-driven inhibition of LPP responses before and after bath application of LY341495. Repeated-measures two-way ANOVA showed a main effect of light (F1,8 = 10.07; P < 0.05; n = 9), a main effect of drug treatment (F1,8 = 29.13; P < 0.001; n = 9), and a significant interaction between both factors (F1,8 = 5.38; P < 0.05; n = 9). Fisher’s LSD post hoc test, control: Light-OFF = 1.32 ± 0.47 mV·s, n = 9; Light-ON = 2.30 ± 0.53 mV·s, n = 9; *P < 0.05. LY341495: Light-OFF = 3.68 ± 0.79 m·s, n = 9; Light-ON = 3.56 ± 0.57 mV·s, n = 9; P = 0.72. (B) Average traces and plots showing abGC-mediated excitation of MPP responses before and after APV. Repeated-measures two-way ANOVA showed a main effect of light (F1,9 = 11.95; P < 0.01; n = 10), no main effect of APV (F1,9 = 1.66; P = 0.23; n = 10), and a significant interaction between both factors (F1,9 = 7.19; P < 0.05; n = 10). Fisher’s LSD post hoc test, control: Light-OFF = 0.84 ± 0.14 mV·s, n = 10; Light-ON = 0.12 ± 0.15 mV·s, n = 10; ***P < 0.001. APV: Light-OFF = 0.88 ± 0.32 mV·s, n = 10; Light-ON = 0.64 ± 0.25 mV·s, n = 10; P = 0.09. (C) Model postulating that the LPP evokes low glutamate release from a small number of abGC, resulting in mGlu-II–dependent inhibition of mGCs. MPP inputs elicit high glutamate release from a larger population of abGCs, leading to NMDAR-dependent excitation of mGCs. (D) Average traces and plots showing the effects of the glutamate uptake blocker TBOA (30 μM) on LPP-evoked responses. Repeated-measures two-way ANOVA showed a main effect of light (F1,8 = 6.81; P < 0.05; n = 9), a main effect of TBOA (F1,8 = 11.38; P < 0.01; n = 9), and a significant interaction between both factors (F1,8 = 64.84; P < 0.0001; n = 9). Fisher’s LSD post hoc test, control: Light-OFF = 1.69 ± 0.23 mV·s, n = 9; Light-ON = 2.63 ± 0.27 mV·s, n = 9; *P < 0.05; TBOA: Light-OFF = 9.19 ± 1.96 mV·s, n = 9; Light-ON = 6.22 ± 1.41 mV·s, n = 9; ****P < 0.0001). Scale bars: 2mV, 50 ms [(A) and (D)]; 0.5 mV, 50 ms (B). All values = mean ± SEM.