By Maggie Fox
Washington - Antidepressants may help stimulate the growth of new brain cells, United States-based scientists said on Thursday in releasing research that may lead to the development of better drugs to fight depression.
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 new insight into how antidepressants work," Dr Thomas Insel, director of the National Institute of Mental Health, said in a statement.
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," Insel said.
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," Hen said in a telephone interview.
"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 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 that the new brain cells in the hippocampus was the source of the lifted depression, Hen and colleagues 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 were then given X-rays, did not resume grooming as would be expected.
Mice who received no X-rays and were killed after being dosed for 11 or 28 days with fluoxetine showed significant growth of new brain cells.
A drug in a different class, the tricyclic imipramine, also stimulated the growth of neurons, Hen's team reported in Friday's issue of the journal Science.
"Besides finding drugs that target this process, the other basic research challenge for me is to find out what the function of these new neurons is," Hen said.
Experts say that 16 percent of Americans - more than 30 million people - will suffer major depression at some point in their lives.
The NIMH says major depression is now the top leading cause of disability around the world.