PROJECT SUMMARY Approximately 1 in 3 American adolescents have been diagnosed with an anxiety disorder; 3 in 20 with a mood disorder, with 1 in 3 female adolescents experiencing at least one major depressive episode. The onset of psychiatric disorders can occur in early life, potentially leading to a reduced quality of life due to a disruption in emotional, psychological, and/or social development. Mental illness during youth may also result in long-term consequences, including an increased risk of mental health challenges and diminished quality of life in adulthood. Inflammation in the central nervous system (neuroinflammation) is thought to underlie anxiety and mood disorders, yet there remain no broadly effective therapies. The neuroinflammatory pathology may be, in part, caused by circadian dysregulation of the neuroimmune system. The circadian clock is critical for controlling biological processes, generating time-of-day differences in gene expression, hormone release, and behaviors; however, circadian rhythms dampen in psychiatric disorders. Although the percentage of individuals experiencing psychiatric disorders concomitant with circadian disturbances remains unknown, circadian disruptions and sleep- wake disturbances are used as diagnosable criteria for neuropsychiatric disorders. Therefore, circadian dysregulation may be a potential biomarker and signal for early intervention in anxiety- and mood disorder- related pathology. The immune system is tightly regulated by the circadian clock, and recent evidence demonstrates circadian regulation of neuroimmune system components: microglia, meninges, and choroid plexus. Microglia, the primary immune cell of the brain, are rhythmic cells that can trigger a release of inflammatory molecules when activated, potentially triggering a suite of physiological and behavioral alterations. The meninges and choroid plexus serve as immune surveillance sites and can also release inflammatory signals that influence the activity of microglia. Together, these components may provide insights into the pathogenesis and pathophysiology of mental disorders. However, the ontogeny of circadian rhythms in the neuroimmune system has not been well-documented. Early developmental periods offer a potential window for intervention and prevention of neuropsychiatric disorders. Thus, we hypothesize that circadian rhythms in the neuroimmune system emerge early in life, and perturbations during development will alter neuroimmune function that leads to behavioral changes. This proposal addresses the following specific aims: First, establish the development of circadian rhythms in “clock” and inflammatory genes in critical neuroimmune tissues; second, reveal whether early life environmental and genetic perturbations to the circadian system lead to long-term behavioral changes. This contribution will be significant because our results will identify temporal windows of high and low neuroimmune reactivity during development. We exp...