Figure 3
Dose-dependent induction of pERK expression and scratching response by histamine. (A, B, E) Thirty min after injection of histamine into the nape region, the number of pERK-positive cells in the spinal cord of mice treated with 500 μg of histamine was significantly increased compared with those treated with 50 μg or 250 μg (A), and the number of scratches recorded in the first 30 min post-injection increased as the histamine dosage increased from 50 μg, to 250 μg to 500 μg (B). One way ANOVA; P < 0.001; n = 6 for each group. The scratch numbers and ERK activation are highly correlated in the dose range from 50 to 500 μg (E). Regression analysis; R2 = 0.86; P < 0.01; n = 5 for 50 μg and 500 μg groups and n = 4 for 250 μg group. (C, D, F) Thirty min post-injection of histamine into the cheek region, pERK-positive cells in the medullary dorsal horn (C) and scratches are increased in number in dose-dependent manner as the doses increased from 10 μg to 50 μg (D). One way ANOVA; P < 0.001; n = 7 for PBS and 10 μg groups, n = 10 for 20 μg and 50 μg groups. Wiping number is maintained at a very low level with no obvious change. One way ANOVA; P > 0.05. Regression analysis of numbers of pERK-positive cells and scratches is shown in (F). Regression analysis; R2 = 0.95, P < 0.01; n = 4 for PBS, 10 μg and 50 μg groups and n = 6 for 20 μg group. *P < 0.05; **P < 0.01.