Antidepressants shown to grow new brain cells

WASHINGTON - Antidepressants may help stimulate the growth of new brain cells, say US scientists.

Research on rats shows that two different classes of antidepressants can help brain cells regenerate - and not in areas normally thought of as being involved in depression.

"This is an important insight into how antidepressants work," said Dr Thomas Insel, director of the National Institute of Mental Health.

The study fits in with others that suggest depression can shrink the hippocampus, a brain region crucial to learning and memory but only recently found to be involved in depression. Major stress and trauma - both depression triggers - can also cause the shrinkage.

"We have known that antidepressants influence the birth of neurons in the hippocampus. Now it appears that this effect may be important for the clinical response," said Insel.

New antidepressants may be developed to target this process directly, said Rene Hen of Columbia University in New York, who led the study.

"The proof in humans is going to come when we extend the work into finding drugs that stimulate neurogenesis. If these drugs have antidepressant effects in humans, this is going to be proof that the process is critical in humans. There is a push already in the pharmaceutical industry to find such compounds."

The new study may also help explain why it can take weeks for antidepressants to give patients relief.

"If antidepressants work by stimulating the production of new neurons, there's a built-in delay," said Mrs Hen. The stem cells that give rise to new cells need time to divide, to differentiate into neurons, move to their new homes and link up with other neurons.

To make sure the new brain cells in the hippocampus was the source of the lifted depression, scientists at Yale University and in France worked with genetically engineered mice, using x-rays to kill newly growing cells in the hippocampus.

These mice did not respond as they normally would to antidepressants. Mice which were given fluoxetine, an antidepressant sold under the brand-name Prozac by Eli Lilly and Co, and then given x-rays did not resume grooming as would be expected.

Mice which received no x-rays and were killed after being dosed for 11 or 28 days with fluoxetine showed significant growth of new brain cells.

- REUTERS