BDNF and depressive disorder: Animal models of stress and depression-like behavior have revealed decreased BDNF expression, as well as loss of synaptic plasticity, particularly in the hippocampus (Duman et al., 1999), as well as restoration of BDNF expression with extended antidepressant treatment (Fujimaki et al., 2000; Coppell et al., 2003; Foubert et al., 2004).