Figure 8

A PKA inhibitor decreases pain-related behavior in arthritic but not in normal animals. KT5720 (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 = 5). In arthritic animals ("arthritis" in A-C; n = 6) KT5720 significantly inhibited vocalizations and increased mechanical thresholds. 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 KT5720 (100 μM) into the striatum as placement control had no effect on audible and ultrasonic vocalizations and on spinal reflexes of arthritic rats (n = 4). Vocalizations were evoked by brief (15 s) noxious (2000 g/30 mm²) stimulation of the knee with a calibrated forceps. Duration of vocalizations was measured as the arithmetic sum of the duration of each individual vocalization event during a 1 min period beginning with the onset of the stimulus (see Methods for details). Bar histograms and error bars show mean ± SE. * P < 0.05, ** P < 0.01, *** P < 0.001 (repeated-measures ANOVA with Bonferroni post-tests).