Figure 7.
Long-term synaptic plasticity. A, Electrical 3D maps for N2a amplitude were obtained before (Pre-TBS) and after (Post-TBS) application of a TBS in three different solutions (control, bicuculline, APV). The subtraction map (Post–Pre) reveals the localization of LTP (red) and LTD (blue). The histograms at the right indicate the percentage of electrodes generating either LTP, LTD, or no change. After TBS delivered in control extracellular solution, LTD prevails over LTP. After TBS delivered in the presence of 10 μm bicuculline, LTP prevails over LTD. After TBS delivered in the presence of 50 μm [scap]d-APV, no remarkable LTP or LTD changes are observed except for a minor occurrence of LTD. The experiments reported in this figure are different from those reported in Figure 4. B, The time course of N2a amplitude changes in control extracellular solution on single electrodes, one showing LTP, one showing LTD, and one showing no long-term plasticity changes [data corresponding to electrodes (2,1), (3,4), and (6,4) in the top right panel of Fig. 6]. C, Time course of N2a amplitude changes in control extracellular solution (circles) and in presence of 10 μm bicuculline (square). The measures were obtained from electrodes showing either positive or negative response variations >10% after TBS (control: n = 50 electrodes for LTD, n = 12 electrodes for LTP, data from 4 slices; bicuculline: n = 16 electrodes for LTD, n = 26 electrodes for LTP, data from 7 slices). D, The left histogram shows that around the LTP electrode, there are on average 3.8 ± 0.7 active granular layer electrodes, 2.2 ± 0.3 of which showing LTD (n = 28 from 6 slices). The right histogram shows the average change in the electrodes surrounding the one with maximal LTP. The net change around the LTP electrode is a significant LTD (n = 28 from 6 slices; **p < 10−5, paired t test). No comparable changes are observed by randomly sampling the granular layer electrodes and measuring the surrounding activity (n = 34 from 6 slices; p = 0.96, paired t test). Error bars indicate SEM.