Figure 6.

Preoperative conditioned pain modulation (CPM) correlated with timecourse of postoperative resolution of mechanical hypersensitivity after partial L5 spinal nerve ligation (pSNL). A, Twenty four hours prior to pSNL surgery CPM was tested in 19 individual rats. Rats produced a variable increase in hindpaw pressure thresholds 30 minutes following intraplantar administration of capsaicin (150 μg/ 50 μl) into the forepaw. Values for individual rats are displayed as a gradient with lower CPM in blue and greater CPM in red. B, Paw withdrawal thresholds to mechanical stimulation were assessed for ten weeks following pSNL surgery and individual daily withdrawal thresholds were recorded. C, Individual repeated daily withdrawal thresholds were analyzed using growth curve analysis to better model the change in mechanical withdrawal thresholds over time. D, The slope of trajectory of withdrawal thresholds correlated to the preoperative difference in CPM as rats with lower endogenous analgesia or CPM had slower resolution of mechanical hypersensitivity. Error bars in D indicate variability in predicted slope over time within individual rats. PPT = paw pressure threshold