FIGURE 2.

Analgesic effects of a single systemic injection (A) or systemic infusion (B) of tempol on paclitaxel-induced neuropathic pain (PINP) in rats. Paclitaxel (PAC, 2 mg/kg) was injected intraperitoneally on four alternate days (days 0, 2, 4, and 6), and the mechanical threshold was measured. (A) On day 20 after the first paclitaxel injection, 24 rats were divided into four groups, which received an intraperitoneal injection of saline or 50, 100, or 200 mg/kg of tempol (5 mL/kg). Note that the mechanical threshold returned to more than 10 g of mechanical threshold (no pain condition in rats) at 0.5 h after the injection of 200 mg/kg of tempol. (B) On day 20 after the first paclitaxel injection, 11 rats were divided into two groups. In the tempol group (N = 6), the rats received an intraperitoneal infusion of tempol (10 mg/day) for 7 days (hatched box) in combination with intraperitoneal injections of tempol (200 mg/kg) on days 20 and 21 (arrowheads). In the saline group (N = 5), the rats received saline (vehicle) instead of tempol. The systemic infusion of tempol significantly increased the mechanical threshold on day 21, and the threshold remained significantly higher than the threshold in the control group for 8 days. The data are expressed as means with standard errors of the means. The asterisks indicate values that are significantly different (P < 0.05) from the corresponding values for the saline group as determined by a two-way repeated-measures analysis of variance with one repeated factor (time) followed by the Tukey post hoc test.