Gender and endogenous levels of estradiol do not influence adult hippocampal neurogenesis in mice

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Abstract
In several species, including rat and vole, the proliferation of new neurons in the adult dentate gyrus (DG) subgranular zone (SGZ) is influenced by both gender and endogenous levels of the gonadotropic steroid hormone estradiol. However, little is known about how adult neurogenesis is regulated by these factors in the mouse. We report here that adult C57BL/6 mice do not have gender differences in hippocampal proliferation or neurogenesis. In addition, the production of new SGZ cells in female mice was not influenced by estrous cycle or after ovariectomy, suggesting that fluctuations in endogenous estradiol levels do not alter adult neurogenesis in the mouse. Both male and female mice had a greater number of BrdU-immunoreactive SGZ cells following chronic treatment with fluoxetine. This demonstrates a parallel proliferation response in both genders, and opens avenues for addressing the neurogenesis hypothesis of depression in female rodents. These findings underscore a distinct regulation of adult neurogenesis in mice vs. other rodents, and are discussed in regard to their implications for the study of adult hippocampal neurogenesis.