Dentate Gyrus Activin Signaling Mediates the Antidepressant Treatment Response

Antidepressants that target monoaminergic systems, such as selective serotonin reuptake inhibitors (SSRIs), are widely used to treat neuropsychiatric disorders including major depressive disorder, several different anxiety disorders, and obsessive-compulsive disorder. However, these treatments are not ideal because only a subset of patients achieve remission. The reasons why some individuals remit to antidepressant treatments while others do not are unknown. Here, we developed a paradigm to assess antidepressant treatment resistance in mice. Treatment of mice with either chronic corticosterone or chronic social defeat stress effectively induces increased negative valence behaviors. Subsequent chronic treatment with the SSRI fluoxetine reverses these behavioral changes in some, but not all, of the mice, permitting stratification into persistent responders and non-responders to fluoxetine. We found several significant differences in expression of Activin signaling-related genes between responders and non-responders to fluoxetine in the dentate gyrus, a region that we recently reported is critical for the beneficial behavioral effects of fluoxetine. Furthermore, enhancement of Activin signaling in the dentate gyrus converted behavioral non-responders into responders to fluoxetine treatment more effectively than commonly used adjunctive antidepressant treatments, while inhibition of Activin signaling in the dentate gyrus converted responders into non-responders. Taken together, these results demonstrate that the behavioral response to FLX can be bidirectionally modified via targeted manipulations of the dentate gyrus and suggest that molecular- and neural circuit-based modulations of dentate gyrus may provide a new therapeutic avenue for more effective antidepressant treatments or adjunctive therapies.