Health

Why Some People Get Stressed Easier Than Others

The dopamine pathway

By Stefan Anitei, Science Editor

22nd of October 2007, 06:47 GMT

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Why are you pulling your hair out while others don't even care about what happens? New molecular brain patterns could explain why some individuals are easy prey for stress.

"While the research was done with mice, the findings could eventually lead to better treatments for chronic stress, depression and the post-traumatic stress disorder suffered by troops in Iraq and other battlefields," said co-author Dr Eric Nestler, chairman of psychiatry at the University of Texas Southwestern

Medical Center at Dallas.

"One important lesson we have shown even in previous papers is that a series of genetically identical animals respond differently to chronic stress. 30 to 40 % seemed to be resilient and did not develop bad symptoms. The clinical implications are that the ability to identify mechanisms of resistance can help provide new and novel approaches to stress." said Nestler.

"The key lies in a pair of molecules used by some brain cells to communicate with one another," said lead author Vaishnav Krishnan, Ph.D and M.D. student in a University of Texas Southwestern Medical Center.

"Under stress, vulnerable mice increase the frequency of nerve activity using the neurotransmitter dopamine. That subsequently causes release of a nerve growth factor called brain-derived neurotrophic factor [BDNF]. Resilient mice overcome these changes by increasing the expression of molecules that prevent the release of dopamine." said Krishnan.

Neurotransmitters have the role of transmitting signals from one neuron to another. The tested mice were so inbred that they had a high genetic similarity. Stress on them was induced by placing them in the cage with bigger, more aggressive mice. Some responded to the induced stress, while others avoided contact, displaying a submissive type of behavior.

The team focused on two brain nuclei - the ventral tegmental area (VTA) and the nucleus accumbens (Nacc), involved in the brain's reward behavior that has a role in survival. Extra BNDF synthesis in highly "stressed" mice took place in the VTA but not the NAcc nucleus.

Signals transmitted by the protein from the VTA to the NAcc turned the mice more likely to experience stress. Drugs blocking those signals turned vulnerable mice into resistant ones.

This could lead to "tools to develop things in the brain that encourage resilience, to help people with stress," Nestler said.
"We have always tried to understand the changes in the brain that lead to such things as the symptoms of post-traumatic stress disorder. This study shows we can increase our understanding and development of new therapeutic measures to overcome those changes." said Krishnan.

"But new therapies might not be easy to develop since a decrease of dopamine or BDNF activity might be helpful in one part of the brain but harmful in another area." said Nestler.

TAGS:

stress | dopamine | brain

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