Serum leptin levels. Values represent mean ± SD for ten rats in each group except the two recovery groups (n = 5). * P < 0.05 compared to control group. + P < 0.05 compared to control recovery group. NT-H: high dose of NT; NT-H-R: high dose NT with a two week recovery period; NT-L: low dose of NT; Pr-fed: pair fed to NT-H group; d-FF: d-fenfluramine.