Project Summary Premenstrual dysphoric disorder (PMDD) is a depressive disorder that impacts women during the luteal phase of their menstrual cycle. Women participating in shift work (work outside of the typical 9 am – 5 pm shifts) have a 50% increased risk of premenstrual disorders, such as PMDD. However, current treatments for PMDD are limited and do not address both the mental health and reproductive symptoms experienced. An improved understanding of the overlap between the impact of mistimed light exposure experienced during shift work, female reproductive health, and mental health is needed to better treat women with premenstrual disorders. Vasoactive intestinal peptide (VIP) neurons within the suprachiasmatic nucleus are a strong candidate population as a shared neuronal origin of the reproductive and mental health problems experienced by shift workers and women experiencing PMDD. VIP neurons from the suprachiasmatic nucleus relay time-of-day information to the brain and body based on the light input received from the eye. VIP neurons also regulate the reproductive gonadotropin-releasing hormone neurons, having an impact on reproductive hormone release, making them a strong target to rescue reproductive and mental health problems. Using a mouse model, I aim to better our understanding of the impacts of light shifts mimicking shiftwork on the body and target VIP neurons to rescue reproductive and mental health problems. Aim 1 will use our novel light shift paradigm to determine the impact of rotating light shifts on reproductive hormone levels, anhedonia, and antisocial behaviors in female mice. Aim 2 will use a targeted viral approach to determine how inhibited suprachiasmatic nucleus VIP neurons in mice drive anhedonia and antisocial behaviors. The findings from this project will give us new insights into the potential mechanism causing PMDD, allowing for more targeted treatments.