Figure 5.

LTD at CI-AMPAR synapses does not involve a change in transmitter release. A, Top, EPSCs recorded at holding potentials between -60 and +40 mV (left) and their corresponding I-V relationship (right). A linear I-V curve (RI, 1.19) suggests that this synapse comprises CI-AMPARs. In all experiments, dl-APV was initially included to block NMDARs for the construction of the AMPAR-EPSC I-V relationship. After determination of the RI, APV was then washed out. Middle, Averages of 10 consecutive EPSCs taken at time points indicated in the bottom dot plot. The right panel shows the normalization of control averaged EPSCs (1) and averaged EPSCs recorded during the first (2) and second (4) application of γ-DGG. Bottom, Mean time courses of EPSCs averaged from eight neurons. In the control epoch, γ-DGG (1 mm) was applied to measure the basal level of inhibition. After complete washout, the high-frequency LTD induction protocol (HFS, 100 Hz for 1 sec, repeated 3 times at an interval of 10 sec) was applied. After LTD had stabilized (3), the same concentration of γ-DGG was applied for a second time. B, EPSCs obtained during the two applications of γ-DGG were normalized to the controls and overlain to illustrate the degree of γ-DGG inhibition before and after induction of LTD. A comparable degree of γ-DGG inhibition was observed before and after induction of LTD. C, γ-DGG-mediated inhibition from eight individual CI-AMPAR synapses before and after the induction of LTD. The filled circles are averages of γ-DGG inhibition before and after the induction of LTD. Open circles are data obtained from individual experiments. Note that the percentage of inhibition by γ-DGG was not significantly different before and after the induction of LTD.