Figure 1.

Intradermal (i.d.) injection of MGO induces itch behaviors in mice. (A-B) Time course (A) and total number (B) of scratching bouts within 30 min induced by i.d. injection of MGO (1-40 μmol) into the nape of neck of mice (n = 5-6 for each group, ^*P < 0.05, ^***P < 0.001 vs. control group, ^### P < 0.001 vs. MGO (10 μmol) group, one-way AVOVA followed by post-hoc Dunnett's test). (C-D) Total number of forelimb wiping (C) and hind paw scratching behavior (D) induced by i.d. injection of MGO (1-10 μmol) into the cheek of mice (n = 5-6 for each group, ^**P < 0.01, ^***P < 0.001 vs. control group, one-way AVOVA followed by post-hoc Dunnett's test). Saline served as negative control. (E-F) Time course (E) and total number (F) of scratching bouts within 30 min induced by i.d. injection of GO (1-10 μmol) into the nape of neck of mice (n = 5-6 for each group, ^*P < 0.05, ^***P < 0.001 vs. control group, one-way AVOVA followed by post-hoc Dunnett's test). (G-H) Total number of forelimb wiping (E) and hindpaw scratching behavior (F) induced by i.d. injection of GO (1-10 μmol) into the cheek of mice (n = 5-6 for each group, ^*P < 0.05, ^***P < 0.001 vs. control group, one-way AVOVA followed by post-hoc Dunnett's test). (I) Pre-incubation of MGO scavengers (aminoguanidine and D-arginine) decreased MGO (3 μmol)-induced scratching behavior in 30 min (n = 5-7 for each group, ^**P < 0.01, ^***P < 0.001 vs. VEH group, Student's t test). (J-K) Naloxone (i.p., 1 mg/kg; J) reduced MGO-induced scratching behavior in mice (n = 5-6 for each group, ^*P < 0.05 compared with NS group, Student's t test), but not for morphine (i.p., 1 mg/kg; K). (L) Second injection of MGO (3 μmol) induced less scratching behavior than that of first injection (n = 7-9 for each group, ^**P < 0.01, ^***P < 0.001 compared with NS group, ^###P < 0.001 compared with 1^st injection group, Student's t test). All data are expressed by means ± SEM. GO, glyoxal; MGO, methylglyoxal; NS, normal saline; VEH, Vehicle.