Changes in relative fura-2 fluorescence ratios in response to externally applied isoguvacine or midazolam in postnatal days 7 rats. Relative ratios represent fluorescence ratios (340/380 nm) normalized to the average of the values during the first 60 s. In the artificial cerebrospinal fluid group (A and B), 10 µm isoguvacine or 0.01, 0.1, or 1 µm midazolam was applied without pretreatment. In the bumetanide group (C and D), 10 µm isoguvacine or 0.1 µm midazolam was applied with pretreatment of 20 µm bumetanide. In the bicuculline group (E and F), 10 µm isoguvacine or 0.1 µm midazolam was applied with pretreatment of 50 µm bicuculline. Midazolam or isoguvacine was applied from 60 to 480 s. The recordings in the control for each group were made without application of midazolam or isoguvacine. A, C, and E show actual changes in relative fluorescence ratios at 10-s intervals from 0 to 480 s. B, D, and F show the mean relative fluorescence ratios during the periods of 0–60 s (baseline), 120–180 s (early phase), and 420–480 s (late phase). Bicu = bicuculline methobromide; Bume = bumetanide; ISO = isoguvacine, MDZ = midazolam. Values are expressed as mean and SEM. *P < 0.05 compared with control at the corresponding period. The numbers of regions of interest are given in the parentheses above the bars representing the baseline value of each condition.