A, typical time course of the event frequency of sIPSCs before, during and after application of 0.5 μM muscimol (○, presence of muscimol; •, absence of muscimol) in the standard external solution with or without 10 μM bumetanide. The number of events for every 10 s time interval is plotted. B, facilitation ratios obtained by application of 0.5 μM muscimol with or without bumetanide. Each bar is the mean of 6 neurons and normalized to the control. The dotted line indicates the respective control. * P < 0.05. C, typical time course of the event frequency of sIPSCs before, during and after the application of 0.5 μM muscimol (○, presence of muscimol; •, absence of muscimol) in Na+-free external solution. The number of events for every 10 s time interval is plotted. D, facilitation ratios obtained by the application of 0.5 μM muscimol in the standard external solution or in Na+-free external solution. Each bar is the mean of 5 neurons and normalized to the control. The dotted line indicates the respective control. * P < 0.05. Note that the muscimol-induced facilitation of sIPSC frequency gradually decreased in the presence of bumetanide or in Na+-free external solution.