Stress and Depression

Some of the symptoms of major depression are helplessness, despair, feelings of being overwhelmed,and a loss of pleasure in activities. The effects of depression also cause a number of changes in the brain. Among these include dopmaine deletion due to prolonged exposure to stress hormones ,and norepinephrine and seretonin depletion. Another change that can occur that many people may be unaware of, is hippocampal shrinkage. Prolonged stress causes cell death in the hippocampal region of the brain. Studies have shown that depressed people have a hippocampus that is 10-20% smaller than normal, which can lead to problems including difficulty learning and remembering information. At this time it is not known exactly what causes the shrinkage in depressed individuals, but is believed to be caused by either death of neurons, or the failure of neurogenesis. The loss in brain tissue and memory problems have been shown to occur in individuals that are no longer depressed. These alarming findings suggest that ways to control neurogenesis could aid in the treatment of depression as well as other psychiatric disorders.(11)

Recent research conducted at the National Institute of Health has found strong evidence to suggest that the antidepressant fluoxitine (Prozac and Sarafem) works by stimulating the growth of new nerve cells in the brain. The study used mice to research the effects of the drug, and found that growth of the new nerve cells induced positive behaviour changes in the mice. Previous research had found that fluoxitine stimulated nerve growth in the hippocampus, but did not show the positive behavioral effects. This research suggests a reason that antidepressants often take a few weeks to take effect. It may be that it takes a few weeks for neurogenesis to occur in the hippocampus. (2) This study shows that the possibility of finding ways to stimulate neurogenesis may greatly aid in treatment of depression, and may repair some of the damage that has occurred in the brain due to hippocampal shrinkage.

Lifestyle

Regular physical exercise such as running has been shown to induce neurogenesis in mice. Sejnowski, Gage, and colleagues compared a group of sedentary mice to mice that ran an average of 4.87 kilometers per day. Mice in the exercise group fared better on memory tests and had 2.5 times more nerve cells than the sedentary group after a one month period.The new nerve cells were concentrated in the dentate gyrus region of the brain. Although this study was not conducted on humans, there is a large amount of evidence showing that regular physical activity, a proper diet, and getting enough sleep can enhance brain function by improving memory and reasoning skills. A healthy lifestyle also eases depression, possibly by inducing neurogenesis.(5) So, although there hasn't been conclusive evidence showing a link between exercise and neurogenesis, the evidence to this date suggests this is the case.