Clinical trials of the company's lead candidate, known as BCI-540, began earlier this year. The drug, originally developed for Alzheimer's disease, boosts brain cell growth by 20 percent. These results are comparable to Prozac. "Because the drug had already been tested in 700 patients, we knew its safety profile," says Schoeneck. (Clinical trials for Alzheimer's were halted because of a high rate of placebo response.) Schoeneck says the drug has so far shown no signs of gastrointestinal or sexual side effects, two of the most problematic side effects of current antidepressants.

The company also plans to test the drug, which shows anti-anxiety effects in rodents, for Post-Traumatic Stress Disorder (PTSD), an anxiety disorder common in combat veterans and assault victims. But the role of neurogenesis in mood disorders is still controversial. "Not everyone is convinced that neurogenesis is integrally related to the cause of depression," says Arnold Kriegstein, director of the Institute for Regeneration Medicine at the University of California, San Francisco.

Drugs that boost brain cell growth may also aid cognition. Previous research has shown that neurogenesis in the hippocampus, a brain area integral to learning and memory, is important for maintaining plasticity in that part of the brain, which in turn is linked to memory function. "With aging, there's a decrease in neurogenesis," says Kriegstein. "The hypothesis is that if you could boost neurogenesis to compensate for that age-related decline, you might maintain functional levels."

BrainCells is also testing a compound, known as BCI-632, for its cognitive enhancing properties. "It's the most neurogenic compound we've seen," says Schoeneck. While the compound hasn't yet been tested in humans, it appears to boost at least one type of memory in rodents. The company aims to begin clinical trials next year.

Novel drug combinations may also have neurogenesis-boosting power. For example, researchers at Brain cells have found that a respiratory drug and a cardiovascular drug, both already on the market, seem to dramatically boost brain cell growth in cellular tests.