Figure 5. Pairing EPSPs with a single postsynaptic action potential (AP) does not induce LTP in pyramidal cells in hippocampal CA1 region of adult wild-type mice.

A, examples of responses during the single spike (left) and burst pairing (right) used in these experiments. B, 100 pulses of presynaptic fibre stimulation (delivered at time = 0) were paired with single postsynaptic action potentials (○, n = 12 cells) or a burst of postsynaptic action potentials (•, n = 13 cells). Postsynaptic spikes were elicited 10 ms after EPSP onset and pairing was done at 5 Hz. The inset shows EPSPs recorded during baseline and 30 min post-pairing in an experiment where EPSPs were paired with single postsynaptic action potentials (left) or a burst of postsynaptic action potentials (right). Calibration bars are 20 ms and 5 mV. B, summary of several experiments like that shown in A where EPSP-spike pairing was performed at different stimulation frequencies. While EPSPs paired with bursts of postsynaptic action potentials induce robust LTP, EPSPs paired with single postsynaptic action potentials failed to induce LTP at all frequencies tested (n = 4–12 cells per group). **P < 0.01 compared to baseline, *P < 0.05 compared to baseline. Postsynaptic infusion of the Na⁺ channel blocker QX314 blocked the induction of LTP by pairing EPSPs with bursts of postsynaptic action potentials (shaded bar, n = 4).