New Insights into Serotonin,
Neurogenesis, and Depression

Princeton neuroscientist Barry Jacobs' career-long study of brain serotonin has provided several new insights into the relationship between serotonin and clinical depression. Based on recent research, he and colleagues propose that the suppression of neurogenesis (the birth of new brain cells) is an important causal factor in the onset of clinical depression. Reciprocally, they theorize that the generation of new neurons may be a factor in recovery from depression, thereby opening up new possibilities for treatment. Jacobs published the review, "Adult Brain Neurogenesis and Psychiatry: a Novel Theory of Depression," with Henriette Van Praag and Fred Gage of The Salk Institute for Biological Studies, in Molecular Psychiatry (2000, Vol. 5.)

A diverse group of studies support the new theory. Stress is believed to be the most significant precipitator of depression. Studies on rats and monkeys that show that stress, probably by means of increased levels of glucocorticoid hormones, inhibits neurogenesis in a region of the hippocampus. Other studies demonstrate that serotonin significantly increases cell proliferation. "It follows," Jacobs says, "that antidepressant treatments that increase brain serotonin, such as drugs like Prozac and electroconvulsive shock, may be effective, at least in part, because they increase the production of new brain cells."

In another line of serotonin research, Jacobs showed the relationship between motor activity and serotonin release in an American Scientist article in 1994. Since then, it has been established that exercise, such as running, has an alleviating effect on depression. Possibly linking the two lines of research is a recent study that shows that wheel-running in mice significantly increases neurogenesis, further supporting the theory that neurogenesis may play a role in recovery from depression.

Interestingly, drugs like Prozac take a few weeks to have an effect on depressive symptoms, while exercise has an almost immediate effect. While more studies are needed in this area, Jacobs says one cause for the therapeutic delay in anti-depressants may be the length of time it takes for new brain cells to fully mature, while exercise bolsters serotonin immediately.

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