Figure 4: QC and SC fibres differ in their responses to chemical stimuli. | Nature Communications

Figure 4: QC and SC fibres differ in their responses to chemical stimuli.

From: Three functionally distinct classes of C-fibre nociceptors in primates

Figure 4

(a) QC afferents responded more vigorously than SC afferents to heat-inactivated cowhage spicules coated either with histamine (10 mg ml−1) or capsaicin (200 mg ml−1) that were inserted into the superficial layers of the skin. For each fibre class, a Friedman analysis of variance (ANOVA) was performed (QC: χ2(15,2)=26.1, P<0.001; SC: χ2(15,2)=25.0, P<0.001). Pairwise comparisons of responses to different chemical stimuli within each fibre class were then performed using Wilcoxon matched pairs test (## and && P<0.01, with Bonferroni correction for multiple testing), comparisons across different stimuli are indicated by red and blue lines for QC and SC fibres, respectively. Responses of QC and SC fibres were compared with Mann–Whitney U-test (**P<0.01, ***P<0.001) and comparisons are indicated by grey bars. Medians are indicated by horizontal lines, boxes represent 25th and 75th percentiles, and whiskers represent 10th and 90th percentiles. (b) Responses to intradermal injection of β-alanine (90 μg per 10 μl) were significantly greater in QC than in SC afferents (***P<0.001, Mann–Whitney U-test). For each fibre class, a Friedman ANOVA was performed (QC: χ2(27,2)=47.4, P<0.001; SC: χ2(32,2)=33.5, P<0.001). Pairwise comparisons within each fibre class were then conducted using Wilcoxon matched pairs test (### and &&& P<0.001; ## and && P<0.01, with Bonferroni correction for multiple testing). Responses between QC and SC classes were compared with Mann–Whitney U-test (**P<0.01, ***P<0.001). Data representation is identical to a. (c) All 27 QC fibres responded to β-alanine, but only 12/32 SC fibres were responsive (χ2(1)=23.65, P<0.001, χ2 test), and none of the MIAs responded. Net responses to β-alanine were significantly larger in responsive QC than responsive SC fibres (**P<0.01, Mann–Whitney U-test). Open symbols correspond to fibres that did not fulfil response criteria. Dashed line indicates net response of 10 APs in 5 min. Data in a are from cynomolgus monkeys only. Data in b and c are from cynomolgus and pigtail monkeys.

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