Optogenetic stimulation of ventral tegmental area dopaminergic neurons in a female rodent model of depression: The effect of different stimulation patterns.

Major depressive disorder is one of the most common mental disorders, and more than 300 million of people suffer from depression worldwide. Recent clinical trials indicate that deep brain stimulation of the superolateral medial forebrain bundle (mfb) can have rapid and long-term antidepressant effects in patients with treatment-resistant depression. However, the mechanisms of action are elusive. In this study, using female rats, we demonstrate the antidepressant effects of selective optogenetic stimulation of the ventral tegmental area's dopaminergic (DA) neurons passing through the mfb and compare different stimulation patterns. Chronic mild unpredictable stress (CMUS) induced depressive-like, but not anxiety-like phenotype. Short-term and long-term stimulation demonstrated antidepressant effect (OSST) and improved anxiolytic effect (EPM), while long-term stimulation during CMUS induction prevented depressive-like behavior (OSST and USV) and improved anxiolytic effect (EPM). The results highlight that long-term accumulative stimulation on DA pathways is required for antidepressant and anxiolytic effect.