LTP of uIPSCs induced at FS→FS synapses but not at non-FS→FS synapses. A, Arrangement of dual whole-cell recordings from a FS-GABA neuron connected with another FS-GABA neuron, as schematically shown at top. At bottom is shown an example of IPSCs of postsynaptic cell (indicated by arrow in the bottom trace) evoked by action potentials generated in presynaptic cell (top trace). Large deflections in the lower trace were generated by current injection to monitor the input resistance of the cell. Each trace is an average of 30 consecutive records. B, Traces at top show examples of uIPSCs recorded at the time point indicated by the same number in the below-plotted graph. Arrow head indicates the time when repetitive stimulation (RS) was given to presynaptic cells. Graph at bottom shows the time course of the mean uIPSC amplitudes recorded from seven FS-GABA neurons. The value was normalized to that before RS. Vertical bars indicate SEMs. SEMs smaller than circles are not shown. C, Arrangement of dual whole-cell recordings from a FS-GABA neuron connected with a non-FS-GABA neuron, as schematically shown at top. At bottom is shown the time course of mean amplitude of uIPSCs of six FS-GABA neurons evoked by action potentials of non-FS-GABA neurons. Examples of uIPSCs recorded at the time point indicated by the same number are shown above. Other conventions are the same as in B. D, The ratio of the amplitude of uIPSCs after RS to that before RS for each pair of cells of the types indicated in the abscissa. Asterisk (*) indicates statistically significant difference at p < 0.05 (unpaired t test).