Figure 4. Activity-dependent, bidirectional RSE.

A and B, representative STP changes induced by 900 pulses at 1 Hz (A), or four 100 pulses at 100 Hz (B). Time courses of fEPSP slopes are plotted in the left panels. The right panels indicate 10 fEPSP slopes normalized to fEPSP₁ in each train on a pseudocolour scale, on which raw field responses were superimposed. The bottom-right panels merge two traces 20 min before and 30 min after LFS or tetanus. D, summary of bidirectional synaptic plasticity and RSE. Changes in fEPSP₁ (red) displayed a BCM-like sigmoid curve (Bienenstock et al. 1982), and they were correlated inversely with the mean changes in fEPSP8–10 relative to fEPSP₁ in each train (ΔSTP ratio, blue), except for four tetani (100 pulses at 100 Hz), which did not alter the STP ratio. In the presence of 1 μm CGP55845, however, four tetani decreased the STP ratio to a degree similar to that after one tetanus-induced LTP. In contrast, one tetanus-induced RSE was blocked by 100 μm SQ22536. AP5 blocked the induction of both LTP and RSE. Data were obtained 15 min before and 30 min after tetanus. *P < 0.05, **P < 0.01 versus basal response; Tukey's test (n = 5–8 slices).