Fig. 1.

Associative pairing precludes LTP in interneurons in the stratum oriens/alveus. (A) Left: Schematic illustrating in-phase high-frequency burst (HFB) stimulation of weak and strong alveus pathways (filled and open symbols, respectively). Sample traces (1 to 5) show action potentials evoked by pairing in one cell. Right: Baseline-normalized EPSP initial slopes (mean ± SEM). (B) Top: Averaged EPSPs recorded before (blue) and after (red) pairing in one cell, showing the interval used to measure the initial slope. Bottom: Baseline-normalized EPSP initial slopes (25 min after pairing) in the two pathways, plotted against one another. (C) Antiphase pairing of two weak pathways induced LTP in seven out of seven cells. Sample traces (left) are from one cell. (D) EPSPs before and after pairing and summary of results, plotted as in (B). (E) Burst stimulation of one pathway also induced LTP. AMPA/kainate receptors were blocked at the end of the experiment (NBQX), to verify that EPSP initial slopes were not contaminated by monosynaptic inhibition. (F) Effect of HFB stimulation of one pathway (weak 1), plotted as for (B) and (D). Traces (top) also show the effect of NBQX. Data in (C) (right) and (E) (right) are shown as the mean ± SEM. Vm, membrane potential.