Figure 4

Analyses of EPSC amplitude evoked by the “minimal stimulation” protocol. A, an overlay of 20 traces of evoked responses to "minimal stimulation" with a theta-pipette electrode recorded in the right CeC from a capsaicin-treated rat. The stimulation intensity was fixed at 20 μA. There were "failure" (no evoked response; green filled arrowhead) and “non-failure” (black filled arrowheads) responses. Numbers in the parenthesis indicate the number of traces grouped according to the event amplitude. B, amplitude distribution histogram of sfEPSCs recorded from the neuron shown in A based on the responses to 20 consecutive stimulation trials (traces contaminated with spontaneous EPSCs or irregular asynchronous noisy events were carefully excluded by visual observation). The peaks in the histogram were classified into "failure" and “non-failure” sfEPSC groups. In this neuron and in many other neurons, “non-failure” sfEPSCs were composed of sfEPSCs with distinct amplitudes (the peaks around distinct values). The estimated "area" of these peaks was calculated by fitting Gaussian distributions onto each peak and the occurrence frequency of the responses belonging to each distinct peak was calculated by dividing each area by the summation of the areas of all peaks identified. In the case of this neuron in B, the occurrence frequency of the failure responses was 69.8%, that of the smaller peak was 9.2% and that of the larger peak was 20.9%. C, distribution of the sfEPSC amplitude for 4 groups. C1, relationship between sfEPSC amplitude of each identified response (x-axis) and its occurrence frequency (y-axis). All identified responses in a total of 132 neurons belonging to different groups are plotted. C2, histograms for the all detected peaks of each sfEPSC amplitude for distinct 4 groups. Y-axis, the pooled total number of detected responses. "Cap L" and "Cap R", neurons recorded in the left (open bars) and right (filled bars) CeC, respectively, from capsaicin-treated SNL rats. "Veh L" and "Veh R", neurons recorded in the left (open bars) and right (filled bars) CeC, respectively, from vehicle-treated SNL rats. The numbers in parenthesis indicate the number of identified responses; in most of the cases, multiple responses were identified from single neurons. D, histograms showing the distribution of weighted average sfEPSC amplitude for each neuron recorded from left (L, open bars) and right (R, filled bars) CeC from capsaicin (Cap)- and vehicle (Veh)-treated rats. Y-axis indicates the number of neurons. The numbers in parenthesis indicates the number of neurons. E, summary of the weighted average sfEPSC amplitude from the neurons recorded from left (L, open bars) and right (R, filled bars) CeC from capsaicin (Cap)- and vehicle (Veh)-treated SNL rats. Mean ± SEM. The numbers in the bars show the number of neurons. ANOVA followed by Bonferroni correction. F, Summary of the failure rate for each neuron group. The abbreviations and the numbers are the same as in E. Mean ± SEM. ANOVA followed by Bonferroni correction. G, Relationship between intensity of the minimal stimulation (x-axis) and weighted average sfEPSC amplitude of each neuron. The abbreviations and the numbers are the same as in E. Spearman's rank correlation coefficient (ρ) was 0.045, which was not significant.