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Recent work with mice has revealed that the antidepressant Prozac spurs growth of new neurons in the brain. Prozac, or fluoxetine, is thought to ease depression by raising the level of the neurotransmitter serotonin in the brain. But now researchers have learned that the drug also causes more neurons to form than normally would. In mice, blocking this growth nullifies the drug's effects on behavior, suggesting that neuron formation may be part of the mechanism that alleviates depression.
How exactly fluoxetine boosts neuron formation, called neurogenesis, is unclear. Neurogenesis consists of several rounds of cell division that create many neurons from a few stem cells. To pinpoint fluoxetine's effect on this pathway, a group at Cold Spring Harbor Laboratory on Long Island, N.Y., created a strain of mouse with neural stem cells that contained a green fluorescent protein in their nuclei, making the cells easy to track under a microscope. They found that fluoxetine works on the second stage of neurogenesis, causing cells called amplifying neural progenitors to reproduce at a 50 percent greater rate than usual. This step is therefore “a clear target for the action of an antidepressant,” which may help in designing better antidotes, says study leader Grigori Enikolopov.
Investigators can use the mouse model to perform more detailed studies of neurogenesis and its relation to mood and of the effects of other depression treatments. The model “is amenable to a wide variety of pharmaceutical and neuroactive stimulation protocols,” says Dennis Steindler, a neuroscience professor at the University of Florida not connected to the research. Enikolopov says he is now studying the drug's effect on neurogenesis in young and pregnant mice, to help assess the risks of antidepressant treatment in human counterparts. Another goal will be to determine whether other depression medications target the same step in neurogenesis.