Fig. 3. Effect of F6 on IPSC amplitude is not dose dependent. (  A ) mIPSCs recorded from a hippocampal pyramidal cell before (  top three traces ) during (  middle three traces ) and after wash-out (  bottom three traces ) of 40 μm F6 show no obvious effect on the amplitude of discrete events. (  B ) Cumulative probability of mIPSC amplitudes before the start of F6 application, at the end of a 20-min-long F6 application and after a 17-min wash-out period. The minor shift toward smaller amplitudes is not reversed upon wash-out. Insets show the amplitude histograms for the three periods analyzed (450–500 events in each period, same cell as in (  A )). (  C ) Mean amplitudes of mIPSCs exposed to F6 of approximately 1 × MAC^pred(n =4) and 2–4 × MAC^pred(n =5) during control, F6, and wash show a trend toward smaller amplitudes after F6 exposure that is only partially reversible (note that only cells with an adequate wash period were included). mIPSCs from five control cells recorded over a similar time period are shown to the right. Note the small decrease in amplitude (run-down). (  D ) Fractional block (mean amplitude in F6/mean amplitude of control)  versus F6 concentration for 13 neurons exposed to F6 (regardless of whether a wash was obtained). The magnitude of the block did not increase with F6 concentration. IPSC =inhibitory postsynaptic current; mIPSC =miniature inhibitory postsynaptic current.