A large rat.
A large rat. Photo by AP
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The stress-inducing tests included being held overnight in a cage filled with wet sawdust, in one case, and in another, being forced to swim. Photo by AP

A team of Israeli scientists is hoping that its research on how rats deal with stress will contribute to our understanding of the causes of depression and suicide.

The study will be presented on Thursday, the final day of the 14th European Symposium for Suicide and Suicidal Behavior, which begins on Monday in Tel Aviv. The lead researcher, Prof. Gil Zalsman, is deputy director and chief of the child psychiatry division of the Geha Mental Health Center and associate professor in psychiatry at Tel Aviv University's Sackler School of Medicine.

Results of the study suggest that while exposure to stress in childhood increases the risk of depression and anxiety, as one might expect, exposure to stress in adolescence may actually provide protection against depression and suicidal behavior later in life. This is the case even for adolescents who were genetically predisposed to suicide, says Zalsman, who calls the finding "surprising."

The study also revealed differences in the responses to stress between rats with a genetic predisposition to depression - meaning they have hormonal and behavioral abnormalities that emulate those found in depressed humans - and rats without a "depression gene." For the study, which was carried out in an animal laboratory at Bar-Ilan University, rats of the Wistar-Kyoto strain, which are genetically predisposed to depression, and Wistar rats, were both exposed to different types of stress at different points in their life cycle. The Wistar rats were the control group. The stress-inducing tests included being held overnight in a cage filled with wet sawdust, in one case, and in another, being forced to swim.

A third group of rats that was exposed to a stimulation-rich environment after undergoing the stress tests during the equivalent of childhood recovered from the traumatic events. According to Zalsman, this indicated that the tendency toward suicidal behavior as a result of exposure to stress is apparently reversible.

Studies from the 1980s, of pairs of twins that committed suicide showed that the risk of the second twin committing suicide after the first twin ended his or her life was 11.3 percent for identical twins, who share all their genetic material, and 1.8 percent for fraternal twins, who do not. And a groundbreaking study led by Israeli scientist Avshalom Caspi and published in the July 2003 issue of Science showed that people with the "depression gene," a short-allele variant of the 5-HTTLPR serotonin-transporter gene, are more vulnerable to stress. As a result, they are at higher risk of developing depression than are people with other variants of the gene.

Since then numerous other studies have been conducted of the gene variant, to contradictory results.

Another study to be presented at the conference is one that looked at bullying as a factor in suicidal behavior. The study found that in the 2005-06 school year, 40.1 percent of adolescent boys in Israel reported having taken part in bullying another adolescent, as did 18.6 percent of adolescent girls. Just slightly fewer adolescent boys, 39.6 percent, and 26.9 percent of adolescent girls, reported having been bullied during this period.

The study was an international one, sponsored by the World Health Organization and published in the International Journal of Public Health in September 2009. Researcher, Dr. Anat Brunstein Klomek, points to a complex relationship between bullying and depression. Brunstein Klomek, of the Interdisciplinary Center's School of Psychology and the Feinberg Child Study Center at Schneider Children's Medical Center of Israel, is part of a Health Ministry pilot project to reduce suicides. She looked at bullying in Israeli schools as well as "cyber-bullying," using social networking sites and other electronic means.

The results indicate that bullying increases suicide risk when combined with other significant risk factors for suicide. Brunstein Klomek cautions, however, that while "media reports generally point to bullying as causing suicide these phenomena are complex and depend on many factors, often including emotional distress such as depression."