Fig. 3. Further characterization of the influence of midazolam on mechanical withdrawal size showed that the area under the curve of the integrated electromyographic (EMG) response to a range of Vfh stimuli was significantly increased in P3 rats but significantly decreased in P40 rats (  A ). Percent increases in the responses (area under the stimulus response curve [AUC]) of individual animals to midazolam 15 min after drug injection (baseline  vs midazolam). Comparisons among the age groups revealed a statistically significant difference in sensitivity to midazolam between the P3 group and both the P21 and P40 groups (  B ). An illustration of the change in the stimulus response profiles after midazolam and saline in the four age groups 15 min after subcutaneous injections. Responses to midazolam (  solid line ) are facilitated compared with saline-treated P3 rats; however, this shifts with increasing age until midazolam prevents electromyographic responses in P40 rats. Responses to saline vary little among the age groups.  Bars indicate mean ± SE. *  P < 0.05, ***  P < 0.001, n = 6–12 in each group. T-2 = threshold minus two hairs; T-1 = threshold minus one hair; T = threshold; T + 1 = threshold plus one hair.