Effects of DAMGO on mechanical thresholds of sensory fibres following nerve injury. (A) Percentages of DAMGO-responding fibres in uninjured and injured nerves. The number of Aδ and C, but not of Aβ, fibres in which DAMGO (100 μM) increased von Frey thresholds was significantly higher in injured compared to uninjured nerves (P < 0.05; Fisher exact test for C fibres, and chi-square test for Aβ and Aδ fibres; calculated on raw data). In uninjured nerves, the number of fibres from sham-operated and nonoperated nerves is the same as in Figure 2. (B) Elevation of mechanical thresholds of Aδ and C fibres in injured nerves by DAMGO (100 μM), and its blockade by DAMGO washout or pre-treatment with μ-opioid receptor antagonist CTOP (100 μM). All Aδ fibres were classified as AM nociceptors. *P < 0.05, compared to all other conditions (1-way RM ANOVA, Bonferroni t test for Aδ fibres, and 1-way RM ANOVA on ranks, Tukey test for C fibres). Data are expressed as means ± SEM. N, number of fibres.