Lack of synaptic modification for glutamatergic synapses onto GABAergic neurons. A, Results from an experiment performed in the same manner as that described in Figure2B except that the postsynaptic neuron was GABAergic. During each cycle of repetitive stimulation, the postsynaptic spike peaked at ∼5 msec after the onset of the EPSP. Calibration: 100 pA, 10 msec for EPSCs; 50 mV, 10 msec for EPSPs.B, Results from an experiment similar to that described in Figure 3A except that the postsynaptic neuron was GABAergic. Postsynaptic spiking was initiated 16 msec before the onset of each EPSP. Calibration: same as in A. C, D, Summary of all experiments with positively correlated (C) and negatively correlated (D) spiking similar to that described inA and B, respectively. The mean percentage change in the EPSC amplitude was −0.3 ± 3.4% (±SEM,n = 5) and −1.7 ± 2.0% (±SEM,n = 4), respectively, for C andD, indicating no significant synaptic change (p > 0.1, t test).