A non-linear relation between levels of adult hippocampal neurogenesis and expression of the immature neuron marker doublecortin

We investigated the mechanisms underlying the effects of the antidepressant fluoxetine on behavior and adult hippocampal neurogenesis (AHN). After confirming our earlier report that the signaling molecule {beta}2-arrestin is required for the antidepressant-like effects of fluoxetine, we found that the effects of fluoxetine on proliferation of neural progenitors and on survival of adult-born granule cells are absent in the {beta}2-arrestin knockout ({beta}2-Arr KO) mice. To our surprise fluoxetine induced a dramatic upregulation of doublecortin (DCX) in the {beta}2-Arr KO mice, indicating that DCX expression can be increased even though AHN is not. We discovered two other conditions where DCX expression is regulated non linearly compared to levels of AHN: a chronic stress model where DCX is upregulated and an inflammation model where DCX is down regulated. We conclude that assessing DCX expression alone to quantify levels of AHN can be misleading and that caution should be applied when label retention techniques are not available. HIGHLIGHTSO_LI{beta}2-arrestin ({beta}-Arr2) is required for the antidepressant-like effects of fluoxetine. C_LIO_LIA dramatic upregulation of doublecortin (DCX) is observed in the {beta}2-Arr KO mice after antidepressant treatment whereas its effects on proliferation of neural progenitors and on survival of adult-born granule cells are absent. C_LIO_LIDCX is more upregulated than the number of young neurons in a mouse model of depression. C_LIO_LIDCX is more down regulated than the number of young neurons in a model of inflammation. C_LIO_LImicroRNAs (miRs) may contribute to the regulation of DCX mRNA expression. C_LI