Monday, April 21, 2008

Exercise and Brain-derived neurotrophic factor (BDNF)

What is the role of exercise in promoting BDNF production?

The capacity of physical activity to maintain and compensate for deterioration of nerve cell function is becoming increasingly recognized. Numerous animal studies have reported that voluntary exercise leads to an upregulation of BDNF. Upregulation simply means that more BDNF is produced. In one rat study, several days of voluntary wheel-running increased levels of BDNF in the hippocampus. This finding is surprising considering that the hippocampus is a structure normally associated with higher cognitive functions such as emotion and memory rather than motor activity. The changes in BDNF levels were found in nerve cells within days in both male and female rats and were sustained even several weeks after exercise.

In particular, running activity increased levels of BDNF in the lumbar spinal cord, cerebellum, and cortex, but not in the striatum. Since the main site of neurodegeneration in people with HD is the striatum, exercise alone will likely not be able to prevent many of the symptoms of the disease. However, exercise can help preserve cognitive function and promote the general health of the brain, as well as the health of the body overall. Although exercise may not be able to promote neurogenesis (the growth of nerve cells) in the striatum, it can promote neurogenesis in other areas of the brain and body and these changes may be enough to delay the onset and progression of various HD symptoms.

There is debate over what intensity of exercise is best to promote brain health. Although previous reports showed that only rigorous exercise, like treadmill running, stimulated BDNF expression, researchers have more recently found that even a light exercise routine may be sufficient. The downside of high intensity is that sometimes this kind of exercise can be a stressful experience that increases the release of stress hormones, thereby canceling the BDNF-promoting effects of exercise. Also, many individuals are simply unable to perform rigorous exercise. These new reports are very encouraging because they indicate that everyone can enjoy the benefits of exercise by simply engaging in light activities such as walking or doing yard work.