Figure 4.

Effects of elevated [K⁺]_o and riluzole on afferent volleys. A, Examples of afferent volley waveforms and the effect of the same conditions shown in Figure 3. Each trace represents the average of six trials under each condition. For each trace, the control (2.5 mm) [K⁺]_o condition is plotted as the black trace. The gray trace represents the experimental conditions indicated by the gray text. Stimulus placement and intensity was optimized for isolation of the afferent volley, although synaptic field potentials are also visible. Arrows indicate afferent volley peaks in the test condition. In these experiments, neither 8 mm [K⁺]_o nor riluzole alone affected the first (conditioning) afferent volley (8 mm [K⁺]_o alone, 99 ± 6% of control; riluzole alone, 91 ± 6% of control; p = 0.98 and 0.21, respectively; n = 9). However, we did detect a significant depression of the conditioning volley in the presence of the 8 mm [K⁺]_o and riluzole combination (31 ± 5% depression; p < 0.01). This was different from the EPSC experiments shown in Figure 3 and may reflect slightly different experimental conditions or differences in statistical power in the two types of experiments. Conditioning field potential slopes were also significantly depressed in the combined presence of riluzole and elevated [K⁺]_o (p < 0.01; data not shown). B, Summary of effect of 8 mm [K⁺]_o and riluzole on afferent volley amplitudes. The combination of 8 mm [K⁺]_o and riluzole caused a significant depression of paired-pulse modulation. ^*p < 0.05 from control; 8 mm [K⁺]_o only and riluzole only conditions (n = 9). C, Summary of effect of the experimental conditions on field potential slope. Eight millimolar [K⁺]_o and riluzole produced significant depression of the field EPSP similar to effects seen on afferent volleys and EPSCs. ^*p < 0.05 from control and 8 mm [K⁺]_o conditions. The combination was different from riluzole alone only at the trend level (p = 0.076; n = 8).