Convergent Effects of Acute Stress and Glucocorticoid Exposure upon MAO-A in Humans

Monoamine oxidase-A (MAO-A), a key brain enzyme which metabolizes monoamines, is implicated in the pathophysiology of stress-related illnesses, including major depressive disorder, addiction, and violent behavior. Chronic stressors and glucocorticoid-administration typically associate with elevated MAO-A levels/activity. However, the relationship of shorter stress or glucocorticoid exposures and MAO-A levels/activity is not well established. Our objectives are to assess effects of acute stress upon MAO-A V-T, an index of MAO-A density, in human brain and acute glucocorticoid exposure upon MAO-A levels in human neuronal and glial cell lines. Twelve healthy, non-smoking participants aged 18-50 underwent [C-11] harmine positron emission tomography to measure brain MAO-A VT on two different days: One under acute psychosocial stress (via Trier Social Stress and Montreal Imaging Stress Tasks) and one under a non-stress condition. MAO-A density (by Western blot) and activity (by [C-14]-5-HT metabolism and liquid scintillation spectroscopy) were measured in human neuronal and glial cell lines after 4 h exposure to dexamethasone. We observed a significant reduction in whole-brain MAO-A binding as reflected by reductions in 10 of 11 brain regions. Acute dexamethasone exposure in neuronal and glial cells significantly decreased MAO-Aactivity and protein levels. We observed a highly consistent relationship between acute stressors and glucocorticoid administration and decreased MAO-A binding, activity and protein levels. Since MAO-A metabolizes monoamines, this phenomenon may explain why acute stressors benefit healthy animals even though chronic stress is associated with illness.