Fig. 2.

Analgesic effect of intraperitoneal (i.p.) injection of a single dose of N-tert-Butyl-α-phenylnitrone (PBN) on established cancer-induced bone pain (CIBP). A single dose of PBN (10, 50, 100 mg/kg, i.p.) was given on day 14 after surgery. The behavioral tests were conducted at 0, 0.5, 1, 2, 4 and 6 h after PBN injection. PBN (i.p., 50 and 100 mg/kg) markedly increased the PWTs in CIBP rats, beginning at 0.5 h, peaking at 1 h and lasing for at least 6 h (*p < 0.05, **p < 0.01, ***p < 0.001 compared with the vehicle group, #p < 0.05 compared with the group treated with PBN 50 mg/kg, n = 6 in each group). However, i.p. injection of PBN at the dose of 10 mg/kg had no significant effect on the PWTs compared with that of the vehicle group (p > 0.05).