The impact of maternal cyanotoxin ingestion on the development and function of the stress axis in offspring. Anthropogenic activities and global warming have increased water eutrophication, which caused a significant increase in the frequency in cyanobacterial harmful algal blooms in freshwaters. This dramatically elevated the production and release of hazardous cyanotoxins, mainly microcystins (MCs), of which MC leucine arginine (MC-LR) is the most abundant and toxic form. Accidental, and sub-chronic exposure to environmental levels of MCs is almost inevitable, through ingestion, inhalation, and/or dermal contact with MC-contaminated drinking water. Evidence indicate that MCs disrupt the mammalian stress response, which in mammals is under the control of the hypothalamus-pituitary-adrenal (HPA) axis. Stressors activate hypothalamic paraventricular nucleus (PVN) neurons to release the neurohormone corticotropin-releasing hormone, which stimulates adrenocorticotropic hormone release from the pituitary to activate release of glucocorticoids from the adrenals. We and others showed that disrupted HPA activity to be linked to promoting anxiety and depression. Our studies in male mice found that sub-chronic ingestion of non-lethal MC-LR levels caused maladaptive HPA activation that may lead to stress-related mental health conditions, such as anxiety and depression. We also found that peripheral correlates of HPA function, such as metabolic activity and microbiome were MC-LR sensitive. Together these data formed the premise that sub-chronic ingestion of non-lethal MC-LR levels causes significant changes in HPA activation in mice. Unlike studies focused on adult animals, prenatal sub-chronic MC-LR effects on the HPA development and function in the offspring have not been studied in detail. In this proposal, we will test the hypothesis that sub-chronic maternal ingestion of non-lethal MC-LR levels disrupts embryonic HPA development and HPA functions in the adult offspring. Aim 1 will determine that sub-chronic maternal ingestion of non-lethal MC-LR levels disrupts the development of brain regions that control stress axis in embryos, while aim 2 will determine that sub-chronic maternal ingestion of non-lethal MC-LR levels disrupts HPA functions in the adult offspring. This proposal will determine the impact of maternal ingestion of MC-LR on HPA development and function in the offspring. This allows for the evaluation of how in utero cHAB toxins in freshwater sources affect the homeostasis and health of the offspring, which is of clinical significance given that it is well-established that disrupted HPA function underlies anxiety and depression.