Hippocampal neuronal dematuration as a common effect of antidepressant treatments

The dentate gyrus (DG) of the hippocampus is one of major targets for antidepressant treatments. Our recent research has revealed that selective serotonin reuptake inhibitor (SSRI) treatment causes a long-lasting change in the phenotypes of mature dentate granule neurons to immature state in adult mouse DG. However, it is unknown whether this dematuration of DG is a common effect of antidepressant treatments and what mechanisms underlie it. Using electroconvulsive stimulation (ECS), a model of highly effective and fast-acting antidepressant therapy, here we show that neural stimulation via ECS induces rapid and lasting dematuration of granule neurons in DG. A single or few times of stimulation transiently reduced mature marker expression and mature synaptic functions. Repetitive stimulation converted this transient dematuration into a stable form lasting more than 1 month. Dematured granule neurons showed higher excitability, and an increase in GABA-mediated inhibition by the benzodiazepine diazepam prevented the lasting maintenance phase of dematuration without affecting the initial induction phase. Our study suggests that dematuration of DG is a common cellular mechanism underlying effects of different types of antidepressant treatments, and demonstrate a novel role for excitation/inhibition balance in bidirectional regulation of the state of neuronal maturation in the adult brain.

4

Imoto Y, Segi-Nishida E, Suzuki H, Kobayashi K