Figure 4. Effects of loperamide on myelinated low-threshold mechanoreceptors.

An experimental protocol identical to that used in C-fibers was employed to investigate the effects of loperamide (5 µg/10µl) on the mechanosensitivity of slowly adapting Aβ- fibers (CV: 26.6 m/s. n = 10) innervating the glabrous skin of the hind paw. A) Loperamide increased mechanical von Frey thresholds significantly (*p<0.05, Wilcoxon matched pairs), but only slightly (median, before vs after: 1.0 g vs 1.2 g shown). Importantly, all afferents remained sensitive to mechanical stimulation. Medians, 25th percentile and 75th percentiles are shown. B). Loperamide (5 µg/10µl) did not significantly change the responses to suprathreshold stimulation (Friedman ANOVA, p: n.s., n = 10). To compare responses to suprathreshold stimulation (8 g) across fibers, each response in a given fiber was normalized by dividing it by each fiber’s grand average, i.e. the average of the responses in the 4 trials prior to injection of loperamide. These normalized data were then used for statistical analysis. Medians, 25th percentile and 75th percentiles are shown.