Dec 22, 2010 15:56 GMT  ·  By

People react differently to stress – some deal with it and once it's gone they go back to a normal life, while some are so affected by it that they develop psychiatric illnesses like depression or PTSD.

It looks the individual resistance to stress is determined by the biological building of each and every one, but the molecular mechanisms behind this are not so clear.

This is what motivated a group of researchers led by Matthias Schmidt at Munich's Max Planck Institute of Psychiatry to carry out several experiments of mice.

So they put young mice through social stress for several weeks, by exposing small groups to new members every three or four days, in order to destabilize any hierarchical structures that might have appeared, forcing each group to fight continuously in order to gain authority.

This type of experiment leads to a measurable hormonal stress reaction that disappears in stress-resilient animals once the cause of stress is removed.

On the other hand, in stress-vulnerable animals the levels of stress hormones remain elevated, just like they would be in the case of depressed patients.

After further analysis, the researchers discovered that stress resilience was influenced by the composition of the AMPA receptor in the brain.

This receptor is composed of four subunits – GluR1 to GluR4, and it acts like a binding partner for the neurotransmitter glutamate.

Since it is an ion channel, it mediates the transmission of electric impulses between nerve cells, influencing perception, feelings, reactions and behavior.

The composition of the AMPA receptor is determined by both genetic and environmental factors, so things are still a bit complex.

The composition of the receptor in terms of subunits GluR1 and GluR2 is important for its ability to allow calcium ions to flow into the cell, triggering an electrical impulse and altering neuronal communication in the brain.

The researchers have shown that stress-vulnerable mice have a low proportion of GluR1 and a high proportion of GluR2, but stress-resilient mice only have a low proportion of GluR2.

A rather interesting fact is that previous studies have shown that the composition of the AMPA-receptor, is linked to measurable changes to short-term memory, and this means that even without any stress at all, mice with a GluR2-rich AMPA receptorwill develop altered neuronal activity and poor memory.

If this link could be turned into a biomarker in humans to determine the composition of the AMPA receptor, than it would be possible to predict individual risk for stress-related diseases.