BDNF and depressive symptom measurement: Increased pro-BDNF levels in the prefrontal cortex and ventral tegmental area, and reduced levels of m-BDNF in the prefrontal cortex and hippocampus are observed in different studies using animal models of depression (Lippmann et al., 2007; Shirayama et al., 2015; Hashimoto, 2016; Zhao G. et al., 2016; Zhao M. et al., 2016).