University of California, Berkeley, researchers have shown that chronic stress generates long-term changes in the brain that may explain why people suffering chronic stress are prone to mental problems such as anxiety and mood disorders later in life.Myelin is stained blue in this cross section of a rat hippocampus. Myelin, which speeds electrical signals flowing through axons, is produced by oligodendrocytes, which increase in number as a result of chronic stress. New oligodendrocytes are shown in yellow. Image by Aaron Friedman and Daniela Kaufer.Their findings could lead to new therapies to reduce the risk of developing mental illness after stressful events.Doctors know that people with stress-related illnesses, such as post-traumatic stress disorder PTSD, have abnormalities in the brain, including differences in the amount of gray matter versus white matter. Gray matter consists mostly of cells – neurons, which store and process information, and support cells called glia – while white matter is comprised of axons, which create a network of fibers that interconnect neurons. White matter gets its name from the white, fatty myelin sheath that surrounds the axons and speeds the flow of electrical signals from cell to cell.