Many areas within the vertebrate nervous system exhibit sex differences in neuron number dependent on the actions of gonadal steroid hormones early in development. The goal of this study is to understand the cellular and molecular mechanisms regulating neuron number in general and is a key step in established where the hormones act in the developing nervous system. In zebra finches, areas of the brain controlling song behavior have more neurons in adult males (who sing) than in adult females (who do not sing). These differences are established by estradiol, which acts during a sensitive developmental period to masculinize the song control centers and instill the capacity for male-typical song. This is a study to identify, in the zebra finch brain song system, cell populations mediating estradiol's regulation of neuron number in two regions of the brain that control song, the high vocal center (HVc) and the robust nucleus of the archistriatum (RA) during sexual differentiation. The investigators have an interesting hypothesis that cells with estrogen receptors migrate into the HVc from surrounding areas of the brain and plan experiments to test this hypothesis. The other new idea to be tested is that estradiol stimulates glial cells (a type of support cell in the brain) and that these glial cells have an effect on the proliferation or survival of neurons in the song centers.
