Fig. 1.

Pain and scratching behavioral analysis following injection of IQ. (A) Dose–response curve for IQ-induced scratching behavior in C57BL/6 mice (n = 4–8/each dose). Inset indicates structure of IQ. (B) Time course of scratching following s.c. injection of IQ (100 μg) (n = 12). The number of scratches is indicated at each 5-min interval during a 30-min test period. (C) Time to onset of scratching after injection of eight different pruritic compounds. Each symbol indicates an individual mouse tested for each compound. The following substances were tested: IQ (100 μg), histamine (100 μg), CQ (200 μg), compound 48/80 (100 μg), 5-HT (100 μg), ET-1 (10 pmol), SLIGRL-NH₂ (100 nmol), and U-46619 (3.5 μg). Seven to eight mice were used for each pruritic compound. (D) Scratching and wiping directed toward the site of injection of each compound into the cheek. The tested compounds are as follows: capsaicin (10 μg), histamine (20 μg), IQ (20 μg), and CQ (20 μg). At least 4–10 mice were used for each substance. (E) Latency to paw withdrawal from radiant heat before (BL) and after IQ injection into a hind paw (n = 10). (F) Paw-withdrawal threshold (g) to von Frey filaments before (BL) and after IQ injection into a hind paw (n = 10). No significant differences at any point were found in both thermal sensitivity and mechanical sensitivity between saline treated and IQ treated groups (P >0.05; two-way ANOVA with Bonferroni correction). The paw-withdrawal theshold or latency time obtained from IQ treated and saline treated groups was compared using two-way ANOVA with Bonferroni correction to test the significance of the difference. All data are presented as means ± SEM.