Fig. 1

PCX model: responses of spinal WDR neurones. (a) Following intraperitoneal injection of PCX (2 mg/kg on four alternate days (n = 16)) rats had significantly decreased paw withdrawal thresholds and increased nocifensive duration after acetone challenge, compared to control treatment (10% cremophor, 5% ethanol in the saline vehicle, n = 15 rats). *p < 0.05, **p < 0.01, ****p < 0.001, ****p < 0.0001, Two-way repeated measure ANOVA with Sidak’s post hoc test. (b-f) On day 28, PCX and vehicle rats were prepared for the electrophysiology recording of spinal wide dynamic range neurones. Recorded WDR neurones from PCX (n = 27 neurones) and control (n = 24 neurones) groups had similar depths in the dorsal horn (b) and similar Aβ and C-fibre latencies (c). Thresholds for Aβ and C-fibre evoked responses were significantly lower in the PCX group, compared to control (d). (e) Post-stimulus histograms (0-800 ms) of the responses of WDR neurones following a train of 16 electrical stimuli (at 3× C-fibre threshold, recorded in 2 ms bins). (f) There were no differences in the magnitude of responses of neurones in the Aβ and Aδ latency band (0-90 ms) between the two groups of rats. (g) There was an earlier time to peak response in C-fibre and PD latency band (90-800 ms) in PCX rats, compared to control. There was a significantly smaller neuronal response in the PD latency in the PCX rats (insert). Analysis with unpaired t test: *p < 0.05 and Mann-Whitney U test: #p < 0.05, ##p < 0.01. Note that > 1 neurone was characterised per rat. Most data expressed as median ± interquatile range except AUC PD in (g) which data were normally distributed