NGF and major depressive disorder: Lower NT concentrations, such as serum BDNF and NGF have been shown to correlate negatively with many affective disorders including bipolar disorder (Barbosa et al. 2014; Lin et al. 2014), major depressive disorder (Brunoni et al. 2008), mania (Tramontina et al. 2009) and obsessive compulsive disorder (Maina et al. 2010).