Figure 6.

Effect of 8 mm [K⁺]_o on afferent volley frequency trains. A, Averaged traces showing the first conditioning (Stimulus 1) and last (Stimulus 10) response from a 10 pulse frequency train delivered at 50 Hz (traces represent six sweeps in each condition). Arrows highlight the afferent volley peak amplitude. Note the depression of the afferent volley by the 10th stimulus in the presence of 8 mm [K⁺]_o. B, Summary of the effect of 8 mm [K⁺]_o on afferent volley amplitudes over a 10 pulse, 50 Hz stimulus train (n = 10). Effects on conditioning peak during 8 mm [K⁺]_o and washout conditions were different only at trend level (p = 0.05). Filled circles, Control amplitudes; open circles, responses in 8 mm [K⁺]_o; filled squares (superimposed on control points), washout. There was a significant effect of elevated [K⁺]_o and a significant interaction between elevated [K⁺]_o and stimulus pulse (p < 0.05; repeated-measures ANOVA). C, Time course and reversibility of 8 mm [K⁺]_o on stimulus-dependent depression. An example from the experiment in B shows the time course of wash-in and washout of the 8 mm [K⁺]_o effect (denoted by solid horizontal bar) on frequency-dependent depression. The dotted line represents the degree of baseline depression before wash-in. D, Effect of elevated temperature on afferent volley trains. At 34°C elevation to 8 mm [K⁺]_o produced statistically significant (p < 0.05; n = 7) frequency-dependent depression, but the effect was quantitatively similar to 25°C only when [K⁺]_o was raised to 9 mm.