BDNF and depressive disorder: In particular, it has been shown that chronic defeat stress, a model of depression, selectively down-regulated in mouse hippocampus the expression of BDNF III and BDNF IV transcripts (corresponding in the present study to BDNF IV and BDNF VIa/b respectively, according to the new nomenclature of BDNF gene), while chronic imipramine treatment reversed this down-regulation [12].