A, fluorescence ratio images (F357/F380) of typical [Ca2+]i in neurons at DIV 29 from a BPTTX-treated culture during the first glycine application (Gly/con), during application of 20 mm KCl (KCl), after adding FPL 64176 (FPL, 1 μm), during the first glycine application in the presence of FPL (Gly/FPL) and after the pulse of glycine (Wash). Calibration bars: 50 μm; higher intensity represents higher [Ca2+]i. B, averages of [Ca2+]i responses to glycine or KCl applications (Gly, 0.5 mm; K20, 20 mm; 15 s pulses, 63 cells) obtained from the culture shown in A under control condition (B1) and in the presence of 1 μm FPL (B2). Note that elevation in basal [Ca2+]i by FPL allows monitoring of the glycine-induced [Ca2+]i decrease, although these cells had been treated chronically with GABAA receptor antagonists and TTX. Same calibration for B1 and B2. All cells were monitored in Hepes buffer.