New York, Jan 9 (IANS): The malfunctioning brain cells are not the only ones to be blamed for depression.

Other non-neuronal brain cells also play a key role in depression - a discovery that may go a long way in understanding, and curing, depression.

Researchers at Hebrew University of Jerusalem have shown that changes in one type of non-neuronal brain cells - called microglia - underlie the depressive symptoms brought on by exposure to chronic stress.

"In addition to the clinical importance of these results, our findings provide the first direct evidence that in addition to neurons, disturbances in the functioning of brain microglia cells have a role in causing psychopathology in general, and depression in particular," said professor Raz Yirmiya, director of Hebrew University's Psychoneuroimmunology Laboratory and lead researcher.

"This suggests new avenues for drug research, in which microglia stimulators could serve as fast-acting antidepressants in some forms of depressive and stress-related conditions," he added.

Nearly every 13th person in India runs a risk of developing an episode of depression during his lifetime, according to a recent study by the World Health Organisation (WHO).

The researchers mimicked chronic unpredictable stress in humans - a leading causes of depression - by exposing mice to repeated, unpredictable stressful conditions for five weeks.

The mice developed behavioural and neurological symptoms mirroring those seen in depressed humans, said the study published in the Journal of Molecular Psychiatry.

The researchers found that during the first week of stress exposure, microglia cells underwent a phase of proliferation and activation and after which, some microglia began to die.

Following five weeks of stress exposure, this phenomenon led to a reduction in the number of microglia and to a degenerated appearance of some microglia cells.

Based on these findings, the investigators treated the 'depressed' mice with drugs that stimulated the microglia and increased their number to a normal level.

"We were able to demonstrate that such microglia-stimulating drugs served as effective and fast-acting anti-depressants, producing complete recovery of the depressive-like behavioural symptoms, as well as increasing the neurogenesis to normal levels within a few days of treatment," said Yirmia.