The glutamate uptake inhibitor PDC increased the amplitude and duration of light-evoked, AMPA receptor–mediated ganglion cell EPSCs. A, Light responses were recorded from an ON–OFF ganglion cell with and without 300 μmPDC. B, PDC increased the peak current for both the ON response (control = −109 ± 28 pA; PDC = −169 ± 40 pA; n = 7; p = 0.01) and the OFF response (control = −88 ± 24 pA; PDC = −131 ± 24 pA; p = 0.04). Asterisksindicate a significant difference between control and PDC here and in subsequent figures. C, PDC lengthened the time from light onset to the peak of the ON response (control = 430 ± 47 msec; PDC = 826 ± 273 msec), but the effect did not reach significance (p = 0.09). The drug had little effect on the time from light offset to the peak of the OFF response (control = 427 ± 44 msec; PDC = 470 ± 65 msec;p = 0.18). D, PDC prolonged the 100–37% decay time (D₃₇) for the ON response (control = 545 ± 112 msec; PDC = 2214 ± 396 msec; p = 0.001) and the OFF response (control = 264 ± 45 msec; PDC = 820 ± 281 msec;p = 0.03). Cells were held at −75 mV. For these experiments and those illustrated in subsequent figures showing AMPA receptor–mediated EPSCs, all extracellular solutions contained 150 μm picrotoxin, 10 μm strychnine, and 50 μmd-AP-5.