Figure 4.

Increase in Q Contributes Only Minimally to Mossy Fiber PTP

(A) Schematic illustration of the experimental approach to measure mEPSCs generated by a single presynaptic mossy fiber terminal. (1) The synapse was first examined in the paired recording configuration, with the presynaptic terminal in the tight-seal, cell-attached configuration. (2) To induce PTP, the presynaptic terminal was then stimulated using HFS_100APs (100 stimuli at 100 Hz). (3) To enable recording of mEPSCs, TTX and TEA were applied immediately after HFS_100APs, and a transition was made from bouton-attached to whole-bouton configuration. (4) mEPSCs were evoked by depolarization of the presynaptic terminal with 4-s pulses from −70 mV to −10 mV. The first depolarizing pulse was applied ∼20 s after HFS. The effect of TTX was verified by the absence of Na⁺ inward currents in the presynaptic terminals.

(B) Traces of mEPSCs evoked by 4-s depolarizations after HFS_100APs (left) and under control conditions (right). The insets show mEPSCs at an expanded timescale after detection and alignment to the onset time point; the white curve represents the average.

(C) Histograms of mEPSC peak amplitude in the same paired recordings as shown in (B). The inset shows an overlay of the corresponding cumulative distributions.

(D) Summary bar graph of the peak amplitude of mEPSCs evoked by 4-s pulses under control conditions (black) and after HFS_100APs (red). Note that the mean value was significantly higher (left), whereas median values were not significantly different (right), indicating a change in the shape of the distribution and a preferential increase in the proportion of large mEPSCs. Data are from 7 pairs. Boxes indicate mean values, and error bars denote SEM.

^∗p < 0.05, ^∗∗p < 0.01.