PROJECT SUMMARY Hormonal contraceptives (HC) are used by 10 million people in the United States alone. While HC have played an important role in revolutionizing women’s health, the impact of HC on the brain have not been well studied, especially during adolescence when HC use often begins. There is a critical need for this knowledge as a growing number of recent studies suggest that use of HC, specifically among adolescents, is associated with subsequent antidepressant use, greater likelihood of developing depression, and increased suicide risk. Adolescence is a critical period of hormone-mediated brain development. Among the brain regions with the most significant maturational changes during adolescence is the prefrontal cortex (PFC), or medial prefrontal cortex (mPFC) in rodents. Because of the extended period of PFC/mPFC development and its well-known role in depression, our central hypothesis is that adolescent exposure to contraceptive hormones may exacerbate the risk for mood dysregulation by perturbing normal PFC development. We will employ daily administration of hormones commonly used in HC (ethinyl estradiol and levonorgestrel) to adolescent rats and examine interrelated endocrine, brain, and behavioral endpoints of relevance to the mPFC. Particular domains of interest in these studies include central steroid hormone levels and receptor expression (Aim 1), synaptic pruning and microglia-synaptic interactions (Aim 2), and long-term programming of behavioral outcomes dependent on mPFC, including stress coping and cognitive flexibility (Aim 3). The research proposed in this application is innovative because it investigates a widely used pharmaceutical for which there is little known about its effects on the brain during an important time of the female lifespan when the potential to shape the trajectory of neural development is high. The proposed research is significant because it is expected to generate knowledge about the effects of adolescent HC use on the female PFC. Ultimately, neuroscientific studies on HC will advance women’s health research and are a much needed step in achieving our long term goal of advancing knowledge of how sex specific factors influence the brain across the lifespan.