New York, Jul 7 (IANS): US researchers have identified a gene that plays a key role in depression by either amplifying or reducing stress, depending on its level of activity -- an advance that may pave the way for treating mental health disorder.

Globally, depression affects over 300 million people annually. Nearly 800,000 die in suicides every year -- it is the second-leading cause of death among people between the ages of 15 to 29, the study said.

The findings revealed that the gene, known as Slc6a15, is found in both animals and humans. By simply altering the levels of this gene in the brain, depression could be triggered in mice, or can make the mice more resilient.

"The study highlights how levels of this gene in these neurons affects mood," said Mary Kay Lobo, assistant professor at the University of Maryland, US.

"It suggests that people with altered levels of this gene in certain brain regions may have a much higher risk for depression and other emotional disorders related to stress," Lobo added.

In the study, published in the Journal of Neuroscience, the researchers focussed on a subset of neurons in the nucleus accumbens called D2 neurons, which plays a central role in the reward circuit.

When mice were subjected to chronic social stress, levels of the Slc6a15 gene in the D2 neurons of the nucleus accumbens was markedly reduced, exhibiting behaviour that indicates depression, such as social withdrawal and lack of interest in food that they normally enjoy.

Conversely, when Slc6a15 levels in D2 neurons was enhanced, the mice showed a resilient response to stress.

In humans, with a history of major depression and people with depression who committed suicide, the gene was found reduced in the nucleus accumbens of these brains, indicating that the link between gene and behaviour extends from mice to humans.

Thus, the research could eventually lead to targeted therapies focused on Slc6a15 as a new way to treat depression, Lobo added.