Sex hormones and adult hippocampal neurogenesis: Regulation, implications, and potential mechanisms

• Androgens increase survival of new neurons in the hippocampus of young adult males.
• Estrogens increase proliferation of new cells in the hippocampus of young adult females.
• Estrogens increase survival of new neurons in the hippocampus of young adult females dependent on type and timing.
• Age and sex modulate the influence of sex hormones on hippocampal neurogenesis.
• Female reproductive history modulates the influence of sex hormones on neurogenesis in the adult hippocampus.

Neurogenesis within the adult hippocampus is modulated by endogenous and exogenous factors. Here, we review the role of sex hormones in the regulation of adult hippocampal neurogenesis in males and females. The review is framed around the potential functional implications of sex hormone regulation of adult hippocampal neurogenesis, with a focus on cognitive function and mood regulation, which may be related to sex differences in incidence and severity of dementia and depression. We present findings from preclinical studies of endogenous fluctuations in sex hormones relating to reproductive function and ageing, and from studies of exogenous hormone manipulations. In addition, we discuss the modulating roles of sex, age, and reproductive history on the relationship between sex hormones and neurogenesis. Because sex hormones have diverse targets in the central nervous system, we overview potential mechanisms through which sex hormones may influence hippocampal neurogenesis. Lastly, we advocate for a more systematic consideration of sex and sex hormones in studying the functional implications of adult hippocampal neurogenesis.