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. 2009 Jan 7;29(1):268–279. doi: 10.1523/JNEUROSCI.4456-08.2009

Figure 4.

Figure 4.

DSI produces both a transient enhancement and a state-dependent decrement of VSI-evoked synaptic currents. A, The experimental protocol is the same as in Figure 2 except that the DSI spike trains ended 5 s before the next VSI spike. VSI was stimulated to fire one spike every 30 s. B, EPSC amplitudes from two recording sessions in the same neurons, one without DSI stimulation (white circles) and one showing three trials of DSI stimulation (black triangles: i, ii, iii). In each trial, DSI stimulation increased the amplitude of the EPSC evoked 5 s after the DSI train, but not 35 s later. The 5 Hz VSI spike train shifted the EPSCs into a potentiated state. In the potentiated state, a DSI spike train transiently increased the EPSC and then caused a prolonged depotentiation (ii). A subsequent DSI train again caused a transient increase, but did not produce any further decrease in EPSC amplitude (iii). C, Plots showing the averaged effects of DSI on the EPSC amplitude in the basal state (i, n = 10), the potentiated state (ii, n = 9), and the depotentiated state (iii, n = 7). In all three cases, there was a significant increase in the EPSC amplitude 5 s after the DSI stimulus (p < 0.001, by paired t test). Insets show example EPSCs before DSI stimulation and 5 and 35 s after DSI stimulation. D, A bar graph showing averaged percentage changes in the amplitude of the EPSCs evoked by VSI spikes 5 s after a DSI spike train. Bars (i, ii, iii) represent data obtained in basal state (i, white), the potentiated state (within 5 min after a VSI spike train) (ii, black), and the depotentiated state (iii, gray). There are no significant differences in the magnitude of changes in the EPSC size among the three (see text). E, A bar graph showing mean values of percentage changes in the amplitude of the EPSCs evoked 35 s after a DSI spike train. Bars (i, ii, iii) are from the same states as in D. The extent of the DSI-evoked decrement was significantly greater during the potentiation state (ii) than during the other two conditions (i, iii) (see text). Asterisks indicate significant differences from the other two bars (p < 0.001 by pairwise multiple comparison by Student–Newman–Keuls method).