FIGURE 3. Loss of Na_v1.8 impairs responsiveness to noxious stimulation in the cold.

a–d, Electrical (a, c) and von Frey (b, d) thresholds of C-fibre terminals in WT and Na_v1.8^-/- mice at 30 °C (open columns) and 10 °C (filled columns). With 1 M TTX (c, d), WT terminals regained excitability in the cold, whereas Na_v1.8^-/- terminals remained unexcitable (n = 10). e, f, C-fibre responses to noxious mechanical stimulation (constant pressure of three times the von Frey threshold) of the terminals at 30 °C (open columns) and 10 °C (filled columns) in WT (e) and Na_v1.8^-/- (f) (52% decrease at 10 °C in WT; 92% decrease in Na_v1.8^-/-; n = 10; see Supplementary Fig. S5). g, Menthol (500 M)-sensitized cold responses of C-fibres in WT (open columns) and Na_v1.8^-/- (filled columns) (4-s bins, two-point adjacent averaging). h, At 30 °C menthol excited C-fibres from WT (open columns) and Na_v1.8^-/- (filled columns) similarly (action potentials per 2 min; see Supplementary Fig. S6b); sensitization to cold occurred only in WT (action potentials per 60 s; n = 7–12). i, Cold-plate test (0 °C). Na_v1.8^-/- mice showed negligible response to noxious cold (n = 9–10). Error bars indicate s.e.m. The boxes in b and d represent the 25th and 75th centiles; the horizontal lines inside the boxes show the median (if not identical with the 25th centile), and the 'whiskers' (enhanced by asterisks) indicate minima and maxima. Asterisk, P < 0.01; two asterisks, P < 0.001; Student's t-test.