Infants with neonatal abstinence syndrome (NAS) experience prolonged hospital stays and poor neurodevelopmental outcomes, in-part because of the lack of accurate, individualized, biologic assessments available to manage this increasingly common medical condition. The proposed study will define the molecular mechanisms that regulate the response to opioid withdrawal in the developing brain by focusing on three candidate microRNAs (let-7a, miR-146a, miR-192) that have been shown to respond to opioid exposure in animal models and adults, and are impacted in both my preliminary study of infants with NAS, and my human neural progenitor cell (NPC) design of opioid withdrawal. By determining the mechanism through which microRNAs impact NPC differentiation in opioid withdrawal, and determining whether exosomal salivary microRNA levels predict treatment dose and neurodevelopmental outcomes in infants with NAS, this study will enhance our knowledge of NAS-related biology and identify potential biomarkers that could improve medical care for this important medical condition.