Project Summary Environmental factors have profound influence on brain plasticity during early-life. Maternal care arguably has the greatest influence on this process, with neglect resulting in an array of mental health issues in adolescents and adults. Childhood adversity (physical abuse, neglect, food insecurity, violence) is estimated to account for up to 45% of child-onset and 32% of adult-onset mental health disorders. Neglect is the most prevalent form of childhood maltreatment in the United States. Neural activity in early life shapes circuit development and can have lifelong consequences on brain function. The prefrontal cortex (PFC) is late-developing, making it more susceptible to early-life adversity. Our previous study revealed that maternal presence/absence from the nest regulates the activity of the PFC of rat pups at postnatal day 11 via the serotonergic system. In this study, we propose to test the relation between PFC activity during early-life and behavioral expression in adulthood. In Aim 1, using single nucleus RNA sequencing, we will test how early-life adversity affects the expression profile of distinct cell populations. Furthermore, using voltage dye imaging, we will test how early-life adversity affects PFC activity in the immediate and long-term. In Aim 2, we will test whether activation or inhibition of the PFC in early- life is causal or protective of long-term behavioral deficits associated with maternal separation. In Aim 3, we will test whether a decrease in serotonergic activity during early-life is sufficient to produce the behavioral deficits observed after maternal separation and, ultimately, whether normalizing serotonin levels in the PFC during maternal separation can prevent the development of behavioral deficits.