Enhanced dendritic morphogenesis of adult hippocampal newborn neurons in central 5-HT-deficient mice

•Hippocampal neurogenesis is enhanced in aged Tph2 CKO mice without central 5-HT.•Increased dendritic length is shown in Pomc+ newborn neurons in aged Tph2 CKO mice.•Dendritic length of newborn neurons is augmented in adult mice without 5-HT neurons.

Serotonin (5-HT) plays an important role in regulating adult hippocampal neurogenesis. Chronic administration of selective 5-HT reuptake inhibitors (SSRIs), which up-regulates extracellular 5-HT concentration, accelerates the maturation of adult-born hippocampal neurons. It is unknown, however, about effects of central 5-HT-deficiency on the dendritic morphogenesis of these newborn neurons. Here, we address this question using two central 5-HT-deficient mouse models, Tph2 conditional knockout mice (CKO) losing central 5-HT from embryonic stage, and Pet1-Cre;Rosa26-DTR (diphtheria toxin receptor) mice lacking central 5-HT neurons exclusively in adulthood. The dendritic length of hippocampal newborn neurons is dramatically increased in these mice. Our findings indicate that reducing central 5-HT can accelerate the dendritic maturation of adult-born neurons, thus revealing a new role of central 5-HT in regulating adult hippocampal neurogenesis.