Olanzapine add-on treatment promotes neuronal differentiation of neural stem cells compared with fluoxetine alone

The addition of olanzapine to fluoxetine produces an antidepressant effect on fluoxetine nonresponders. Promoting hippocampal neurogenesis is associated with the successful treatment of depression. The present study aimed to investigate the interaction of olanzapine and fluoxetine in regulating neurogenesis. We found that fluoxetine alone does not affect cell proliferation and inhibits the neuronal differentiation of cultured neural stem cells (NSCs), but promotes NSCs proliferation and exerts no effect on neuronal fate when NSCs are cocultured with neurons. In addition, fluoxetine alone also does not alter the neuronal fate of newborn hippocampal cells in vivo. Although fluoxetine treatment elicits different results, our data consistently show that olanzapine alone does not affect the proliferation and neuronal differentiation of NSCs. The combination of olanzapine and fluoxetine has no profound effect on NSCs proliferation compared with fluoxetine alone, but olanzapine add-on treatment produces a greater number and percentage of differentiated neurons from NSCs. Further investigations are needed to explore the underlying mechanisms of the increased neurogenesis caused by the combination of olanzapine with fluoxetine.