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updated 2/9/2011 1:08:59 PM ET 2011-02-09T18:08:59

Your levels of a certain brain protein could affect how you respond to stress and could even increase your risk for depression, a new study suggests.

People with depression were twice as likely as people without depression to have low levels of neuropeptide Y, a brain molecule that helps to restore calm during stressful events, the study said.

Your levels of neuropeptide Y are determined by your genetics, and the finding provides more evidence that our stress response and even susceptibility to depression are at least partially determined by genes, said study researcher Dr. Brian Mickey, an assistant professor in the Department of Psychiatry at the University of Michigan Medical School.

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"We found [people with low levels of neuropeptide Y] had a more negative emotional experience during stress" than people who had normal or high levels of the brain molecule, Mickey told MyHealthNewsDaily.

They also had greater psychological responses to pain, he said.

The study was published yesterday (Feb. 7) in the Archives of General Psychiatry.

Putting the genes to the test
Mickey and his colleagues studied people's neuropeptide Y levels and responses to stress with two tests.

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In the first test, the researchers showed 93 people neutral words (such as "material"), negatively tinged words (such as "murderer") and positively tinged words (such as "hopeful") and tested their brain responses.

The researchers found that people with low levels of neuropeptide Y had a stronger response to negative words in their prefrontal cortex, the part of the brain that processes emotion, than people with high levels of neuropeptide Y.

This demonstrated that this brain region is activated in people with low neuropeptide Y levels even before real stressors or symptoms begin, Mickey said.

In the second test, the researchers injected saline solution into the jaws of 96 people, which causes pain for about 20 minutes.

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The study participants rated how positive and negative they felt before and after the injection. People with low neuropeptide Y levels were more likely to report negative emotions before and after the injection than people with high levels, the study said.

Scientists then looked at the genes of the people in the study to see if they had the variation that would bring low levels of neuropeptide Y. They found that 40 percent of people with depression had low neuropeptide Y levels, whereas only 20 percent of people without depression had low levels of the brain molecule, the study said.

The right genes
Not everyone with the genetic variation that spurs low neuropeptide Y levels will develop depression, Mickey said.

"Genes are only half of the story. The other half of a person's risk for depression derives from early adverse experiences, recent life stress [and] medical illness," Mickey said.

The study demonstrates that, just like in any other illness, our susceptibility to depression is affected by our genes, said Dr. Eva Redei, a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine, who was not involved with the study.

Neuropeptide Y is "protective — that was the belief based on a lot of evidence that increased neuropeptides actually promote resilience to stress," Redei told MyHealthNewsDaily.

Past studies have shown that genes impact the levels of neuropeptide Y our bodies produce. One study, published in 2010 in the journal Human Mutation, showed that a specific gene variant was important in regulating gene expression of neuropeptide Y and affecting brain function.

The new study is very supportive of other preliminary research that has been published, Redei said.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @ AmandaLChan.

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