-
> From Nature: Science Update
New nerves may fight depression
Prozac and other antidepressants may boost brain-cell birth. 08 August 2003
HELEN PEARSON
Common antidepressants such as Prozac lift mood by spawning new brain cells, suggests a new study. The finding might give rise to more potent drugs that directly boost nerve production.
The report attempts to solve a conundrum: why many antidepressants take several weeks to take effect despite boosting brain chemicals within days. This applies to selective serotonin re-uptake inhibitors (SSRIs), which raise available levels of the nerve-to-nerve signal serotonin, and tricyclic antidepressants, which bump up norepinephrine levels.
The drugs work by triggering the birth of new nerve cells in the hippocampus, normally associated with learning and memory, argue René Hen of Columbia University, New York, and his team. In mice, they found, jamming new nerve birth scuppers some of antidepressants' uplifting effects.
To cripple neuron production, the group trained an X-ray beam on some animals' hippocampus; this treatment kills only dividing cells. X-rayed mice suffered more fear and stress after month-long courses of Prozac — an SSRI — or of the tricyclic antidepressant imipramine.
The study offers some of the best evidence that the new cells are responsible for at least some of the mood-lifting effects of antidepressants; rather than being merely a side-effect. "This is as good as it gets right now," says brain researcher Elizabeth Gould at Princeton University in New Jersey.
Critics point out that the drugs may have other effects in the brain that help to fight depression. What's more, it is difficult to mimic the human disorder by testing anxiety in mice. "We have no idea how relevant this is to human depression," says Daniel Weinberger, who studies mental illness at the National Institute of Mental Health in Bethesda, Maryland.
Making connections
An estimated 121 million people worldwide suffer clinical depression; almost one in ten in some developed nations. Antidepressants are the world's third most widely prescribed drugs.
The idea that antidepressants might generate new hippocampal neurons was first proposed in 2000. Hen suggests that young neurons may stave off depression because they are more adept at forming and re-forming connections, helping the brain to accommodate stress.
A new generation of mood-enhancing drugs might even be designed to prompt hippocampal cells to divide, he speculates.
References
1.Santarelli et al. Requirement of hippocampal neurogenesis for the behavioral effects of antidepressants. Science, 301, 805 - 809, (2003).|Homepage|
© Nature News Service / Macmillan Magazines Ltd 2003