Elevation of postsynaptic calcium through L-type Ca²⁺ channels is necessary to induce LTPi.

<p>(A) Representative eIPSC traces recorded from two pyramidal neurons before (baseline) and 20 min after LTPi-inducing depolarizing steps. The left neuron was intracellularly perfused with 0.2 mM EGTA (Ctr), the right neuron with 20 mM BAPTA. Note that in the presence of the fast Ca²⁺ chelator LTPi could not be induced. (B) Population time courses of normalized IPSCs in the two conditions of (A). (C, Left) Representative eIPSC traces recorded from a pyramidal neuron expressing LTPi in the presence of the NMDA receptor antagonist (D-APV, 50 µM). (C, Right) Representative eIPSC traces of another pyramidal neuron, in which LTPi was prevented by the L-type Ca²⁺ channel blocker nifedipine (10 µM). (D) Population data plots of the two pharmacological applications of (C). (E) Plots of individual eIPSC amplitudes before (<i>x</i>-axes) versus 20 min after depolarizing steps (<i>y</i>-axes) in control (ctr), D-APV, and nifedipine. In (C–E), white, grey, and black symbols refer to control, D-APV, and nifedipine, respectively. Data are single values and/or mean ± SEM. **<i>p</i><0.001; ***<i>p</i><0.0001. Further analyses are illustrated in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001903#pbio.1001903.s004" target="_blank">Figure S4A</a>. Numbers 1 and 2 refer to times of trace illustration.