Molecularly, decreased histone acetylation induced in some brain regions (e.g. hippocampus and nucleus accumbens) by stressors was involved in the dysregulation of the stress-related neurotransmitter systems such as the DAergic and serotonergic systems (e.g. decreased synthesis of DA and serotonin), as well as anxiety- and depression-like behavioral alterations, and HDAC inhibitors regulatorily antagonized both molecular and behavioral effects [115, 116]. This evidence concerns the gene HDAC9 and major depressive disorder.