Depressed loner mice get more sociable when researchers delete a memory molecule from their brains, scientists say.This molecular therapy worked about as well as giving mice antidepressants, the researchers report today in the journal Science.

The finding might help treat human ills like social phobia and post-traumatic stress, the scientists say. They targeted a molecule in a section of the brain known to be related to sensations of pleasure and danger, says Dr Olivier Berton of the University of Texas Southwestern Medical Center, one of the report's authors. "We focused on this molecule in a region of the brain that people call the reward pathway, which people have studied a lot in relation to drugs that are abused," he says.

Deleting the molecule from this part of the brain meant that the mice were never depressed and fearful, Berton says, even though conditions were set up that normally would make them run and hide. "If we can identify such mechanisms in the brain, that's a way to develop antidepressants that work faster and in more people," Berton says.

Depressed mice become withdrawn
To carry out the experiment, Berton and his colleagues had to find a way to reliably make mice depressed. They did this by putting ordinarily sociable mice in cages with aggressive, bullying mice. The sociable mice regularly fought with the bullies, and over a period of days became withdrawn and fearful of strange mice. Even when the bullies were removed, the depression stayed. They perked up when dosed with antidepressants for a month, Berton says.