The effect of postnatal age on somatosensory-evoked potentials evoked by C-fiber electrical hind paw skin stimulation. (A) Typical recordings of right somatosensory-evoked potentials after electrical stimulation of the left hind paw (10 × 3.2 mA, 500 μs stimuli applied at the time indicated by the dotted line). Recordings were performed at 1.5% inspired isoflurane (Iso 1.5%) and during 5-min step increases (step 1: 2%; step 2: 3%; step 3: 4%; step 4: 5%) in rats aged postnatal day (P) 7, P14, P21, and P30. Traces represent grand average evoked potentials (filled lines) ± SEM (gray area) from 10 stimuli per animal (n = 7 animals). Note the different y-axis scale at P7 compared with older ages. (B) Comparison of the evoked potential peak amplitude at each Iso step, normalized to initial values obtained during Iso 1.5% (repeated measures ANOVA, P7: F_{(4, 24)} = 78, P < 0.0001; P14: F_{(4, 24)} = 37, P < 0.0001; P21: F_{(4, 24)} = 17, P = 0.0008; P30: F_{(4, 24)} =49, P < 0.0001 and Dunnett post hoc multiple comparisons test: **P < 0.01, and ***P < 0.001, compared with evoke peak amplitude during inspired Iso 1.5%).