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The role of adrenarche in the evolution of the human brain

Rafaela Takeshita, Ph.D., Anthropology, Â鶹ÊÓƵ

Wilson Chung, Ph.D., Biological Sciences, Â鶹ÊÓƵ

Changes in peripheral and central steroid concentrations in primates have profound effects on brain development and major implications for cognitive development. In particular, adrenal hormones are associated with longevity and brain maturation, making them pivotal for understanding human brain evolution. Previous studies in primates reported interspecies difference in circulating concentrations of dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulfate (DHEAS) and in the timing of adrenarche (i.e., postnatal increase in the release of these hormones). High concentrations of DHEA/S have been hypothesized to enhance brain complexity, being therefore crucial for the evolution of human cognition. Indeed, humans have the highest circulating levels of DHEA/S, and an extended adrenarche amongst primates. However, the extent to which adrenarche contributes directly to brain development is unknown. This project will examine brain changes in DHEA/S levels from central and peripheral secretion in human and chimpanzee brain. Total secretion of DHEA/S will be examined by enzyme immunoassay in the hippocampus and striatum of humans and chimpanzees before, during, and after adrenarche. In addition, we will examine the ability for central DHEAS production in these two species by investigating age-changes in gene expression of key steroidogenic enzymes necessary for DHEA/S production in the brain of these two species. This study will have a major impact in our understanding of brain development, and it will be pivotal for determining to what extent adrenal hormones contributed to brain evolution.