Effect of RTX on Aδ and C responses at the mid-plantar injection site. Either 5 or 50 ng of RTX was injected into the right while vehicle was injected into the left hind paw. Aδ and C responses before and after injections were followed for several weeks. (A-D and F) Aδ responses following intraplantar RTX-injection. We used probability of withdrawal (A, C and F) and the intensity of withdrawal (B and D) as endpoints for the Aδ assay. Behavioral responses to stimulus intensities at 5.12 W/mm2 (A, B and F) or 6.08 W/mm2 (C and D) are shown. (E) Loss and return of C-fiber responses after RTX-intraplantar injection. We used latency to paw withdrawal as the endpoint for the C-fiber assay; a stimulus intensity was chosen that produced a response latency of ~8 sec in normal rats. A cutoff of 16 sec (dashed line) was imposed to prevent tissue damage. (F and G) Direct comparison of behavioral responses at day 18 post-RTX to Aδ (F) and C (G) stimuli. Data used in week 3, in the line graphs, are the average of tests done on days 16, 18 and 21. Hypoalgesia at day 18 was maintained in Aδ but not C-fibers. The tables under the graphs denote statistical comparisons between vehicle and 5 ng or 50 ng RTX, which are aligned with the post-treatment time points. Each data point is an average of the combined responses from 2 or 3 non-consecutive days of testing during the time period indicated on the x-axis (weeks). For graphical simplicity, the data from all vehicle-treated rats (n = 12) is combined, yielding a single line in the plots, since there was no significant difference between the two vehicle groups. 2-way ANOVA with repeated measures was used to compare the effect of 5 ng or 50 ng RTX versus vehicle. 2-way ANOVA was used to compare the effects of 5 ng versus 50 ng. Fisher's exact test was used in F. *,† p < 0.5, **,†† p < 0.01, ***, ††† p < 0.001, n = 6 rats per group.
Mitchell et al. Molecular Pain 2010 6:94 doi:10.1186/1744-8069-6-94