Fig 1.

Withdrawal thresholds to tactile stimuli applied to the face (A) and the hindpaw (B) were measured in rats prior to any surgical manipulations (naïve) and immediately prior to dural application of inflammatory mediators (IM) or synthetic interstitial fluid (SIF) (baseline). There were no significant differences (P > 0.05) between the responses of naïve rats and those receiving SIF, indicating that surgery alone did not produce a sensitization of the face or hindpaws to tactile stimuli. Withdrawal responses to tactile stimuli applied to the face and hindpaws developed slowly over time and reached a maximal decrease in threshold 3 hr after administration. Withdrawal responses to stimuli applied to the face and hindpaws approached baseline values 5 hr and 6 hr, respectively, after IM administration. For both facial and hindpaw responses, 2-factor ANOVA indicated that response thresholds of IM-treated rats were significantly (P < 0.0001) less than those of SIF-treated rats.