Cutaneous nociceptors lack sensitisation, but reveal μ-opioid receptor-mediated reduction in excitability to mechanical stimulation in neuropathy

Table 1 Effects of DAMGO on mechanical thresholds of sensory fibres in uninjured and injured nerves

Fibre type	Group	Uninjured nerves			Injured nerves
		Numbers	Baseline (g)	DAMGO (g)	Numbers	Baseline (g)	DAMGO (g)
Aβ	All fibres	n = 68	0.14 ± 0.02	0.15 ± 0.02	n = 46	0.11 ± 0.02	0.11 ± 0.02
	DAMGO-responders	n = 2	0.22 ± 0.09	0.42 ± 0.12	n = 0	-	-
	DAMGO-nonresponders	n = 66	0.14 ± 0.02	0.14 ± 0.02	n = 46	0.11 ± 0.02	0.11 ± 0.02
Aδ	All fibres	n = 65	0.35 ± 0.05	0.38 ± 0.05	n = 93	0.40 ± 0.04	0.65 ± 0.08 *
	DAMGO-responders	n = 4	0.25 ± 0.11	0.69 ± 0.13	n = 28	0.38 ± 0.06	1.19 ± 0.23
	DAMGO-nonresponders	n = 61	0.35 ± 0.05	0.35 ± 0.05	n = 65	0.44 ± 0.07	0.44 ± 0.07
C	All fibres	n = 19	0.61 ± 0.14	0.72 ± 0.17	n = 39	0.64 ± 0.09	1.03 ± 0.18 *
	DAMGO-responders	n = 3	0.98 ± 0.15	1.69 ± 0.40	n = 18	0.70 ± 0.13	1.56 ± 0.31
	DAMGO-nonresponders	n = 16	0.54 ± 0.15	0.54 ± 0.15	n = 21	0.59 ± 0.12	0.59 ± 0.12

DAMGO was applied at a concentration of 100 μM. N represents the number of fibres, and g refers to the fibre thresholds. *P < 0.05, compared to the respective baseline thresholds (Wilcoxon test). No statistical evaluation was performed for DAMGO-responders or DAMGO-nonresponders in uninjured or injured nerves. In uninjured nerves, the number of fibres from sham-operated and nonoperated nerves is the same as in Figure 2. Data are expressed as means ± SEM.

ISSN: 1744-8069