Figure 3

Low dose zymosan caused smaller, more transient pain behaviors in rats fed normal chow. Baseline measurements (average of 2) are plotted on postoperative day (POD) 0. On POD 0, the L5 DRG was injected with 10 µL incomplete Freund’s adjuvant (IFA) containing either 20 µg of zymosan (“regular dose zymosan”) as used in our previous studies, or 2 µg of zymosan (“low dose zymosan”). The regular dose caused a marked decrease in von Frey paw withdrawal threshold (PWT; A), and an increase in mechanical allodynia (withdrawal response to stroking with a cotton wisp; B) and cold allodynia (withdrawal response to a drop of acetone on the paw; C). These responses were significantly different from baseline starting on POD 1 and were maintained on all subsequent days of testing (one-way ANOVA with Dunnett’s posttest within the regular dose group; F_{(5, 42)} = 1032 for von Frey data, 30.2 for mechanical allodynia data, and 8.1 for acetone data). However, in the low dose group, the magnitude of the zymosan-induced pain behaviors was markedly attenuated, and differed significantly from baseline only in the von Frey test at POD 1 (one-way ANOVA with Dunnett’s posttest within the low dose group, F_{(4, 35)} = 3.9 for von Frey data, 1.5 for mechanical allodynia data, and 1.3 for acetone data). N = 8 Sprague-Dawley rats per group. Each group contains equal numbers of male and female rats; no obvious sex differences were observed so data from males and females have been combined. Data from the “regular dose zymosan” group are contemporaneous data taken from our recently-published study³¹. ***p < 0.001, significant different between the 2 groups at all post-baseline time points, 2-way repeated measure ANOVA with Sidak’s multiple comparison posttest; F_{(1, 14)} = 633.7 (A), 495.2 (B), and 91.9 (C).