Comparing the serum BDNF, NT-3, and 5-HT levels in patients having varying degrees of depression (\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{upgreek}\usepackage{mathrsfs}\setlength{\oddsidemargin}{-69pt}\begin{document}$\overline{x}$\end{document}x ̄± s). This evidence concerns the gene BDNF and major depressive disorder.