Comparison of the repetitive discharge characteristics of DRG cells evoked by dorsal root stimulation between control and neuropathic (NeP) rats. Dorsal root repetitive discharge characteristics were tested by measuring the refractory interval of two APs elicited by paired pulse stimulation of the dorsal roots. A. Scatter plots showing the distribution of the refractory interval variables with the median (horizontal line) superimposed in each case. Asterisks above the graph indicate a significant difference between control and neuropathic animals. *p < 0.05, **P < 0.01; ***p < 0.001. Abbreviations are as indicated in Figures 2 and 4. B. Representative examples of somatic APs evoked by paired pulse dorsal root stimulation with variable inter-stimulus intervals. (a) a MS neuron in a control rat (interval 0.3, 0.2 ms), (b) a MS neuron in a neuropathic rat (interval at 1.8, 2 ms). The data show a longer refractory interval in neuropathic rats. (c, d) MS neurons in neuropathic rats (left: interval: 1.6, 1.5 ms; right: interval: 2.5, 2.6 ms). The data show not only a longer refractory interval but also a delayed second AP response to the second stimulus. (e) a MS neuron in a neuropathic rat (interval. 5.5, 5, 4.5, 4, 3.5, 3 ms). The data show that the second AP failed at an interval of 3 ms, the second AP was delayed at 3.5 ms and the second AP was elicited when at an interval of 4 ms.