A key to depression

November 02, 1999

PROZAC stimulates the birth of new brain cells in rats, say scientists from New Jersey. The finding gives clues to what causes depression in people, how drugs like Prozac relieve it and why the effect takes so long to kick in.

Just over a year ago, researchers showed that people grow new neurons all the time. This overturned a long-held belief that brain cells, unlike cells in other parts of the body, are not replaced when they die.

Barry Jacobs and Casimir Fornal at Princeton University put together findings from several different brain studies. They knew, for instance, that depressed people have a smaller hippocampus-a structure that is involved in learning and memory-than healthy people.

They also knew that chronic stress can slow neuron birth, or neurogenesis, in the brains of rodents. Stress is thought to contribute to depression. "A little light went on in my head," says Jacobs. "It just occurred to me that maybe this is what depression is all about."

Jacobs and Fornal went on to show that activating one type of receptor for the neurotransmitter serotonin in rats' brains increased the birth of neurons. So they decided to see if Prozac, which belongs to a class of drugs known as selective serotonin re-uptake inhibitors (SSRIs), would have the same effect. SSRIs prevent serotonin from being mopped up, leaving more of it around to transmit messages.

The team gave daily injections of Prozac to five rats for 21 days. Five control rats were injected with saline. During the final 7 days, they also gave the rats a chemical called BrdU, which labels new neurons. When they examined the rats' brains, 69 per cent more new neurons had appeared in the brains of the Prozac-treated rats compared with the controls.

Jacobs and Fornal believe that the waxing and waning of neurogenesis in the hippocampus may be an important factor in explaining why people slump into depression and why they recover with SSRIs. It may also explain why Prozac takes several weeks to improve mood. "The time needed for these newly generated cells to mature and make appropriate connections provides an explanation for the 'therapeutic lag' in antidepressant therapy," Jacobs told the meeting.

Jacobs thinks serotonin could also help to treat other neurological diseases, such as Alzheimer's. But he cautions that it probably won't be of use to healthy people: "Their level of neurogenesis might already be optimal."
-end-
Author: Alison Motluk

New Scientist issue 6 November 99

PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO : http://www.newscientist.com

New Scientist

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