Figure 9

An ERK inhibitor decreases pain-related behavior in arthritic but not in normal animals. U0126 (100 μM, concentration in microdialysis probe, 15 min) administered into the CeLC had no significant effect on audible (A) and ultrasonic (B) vocalizations and on hindlimb withdrawal reflexes (C) in normal animals ("normal"; n = 3). In arthritic animals ("arthritis" in A-C) U0126 significantly inhibited vocalizations (n = 9) and increased mechanical thresholds (n = 5). In the arthritis group, behaviors were measured before (baseline) and 6 h after arthritis induction and during (15 min) and after (30 min washout) drug application. (D-F) Administration of U0126 (100 μM) into the striatum as placement control had no effect (n = 4). Vocalizations and withdrawal reflexes were measured as in Figure 8 (see Methods for details). Bar histograms and error bars represent mean ± SE. * P < 0.05, ** P < 0.01, *** P < 0.001 (repeated-measures ANOVA with Bonferroni post-tests).