Figure 2.
Antinociceptive effects of acute nicotine in preproenkephalin-deficient (black bars) and wild-type (white bars) mice. Antinociceptive responses in the hot-plate (A) and tail-immersion (B) tests were measured at 15 and 16 min, respectively, after nicotine administration (0, 1, 3, and 6 mg/kg, s.c.). Data are expressed as mean ± SEM of percentage of maximum possible effect (MPE) in wild-type (saline, n = 34; nicotine, 1 mg/kg, n = 21; nicotine, 3 mg/kg, n = 19; nicotine, 6 mg/kg, n = 14) and knock-out (saline, n = 33; nicotine, 1 mg/kg, n = 17; nicotine, 3 mg/kg, n = 17; nicotine, 6 mg/kg, n = 15) mice. ★★p < 0.01, when compared with the saline group of the same genotype. ☆p < 0.05, comparison between genotypes (Dunnett's test).