Bullied mice show how brain reacts to social stress

[Luba]

from CNEWS:

WASHINGTON - Any bully's victim knows the experience can cause lingering fear. Now scientists watching big mice intimidate small ones have discovered the stress spurs genetic changes in the brain - a finding that may help research into depression and other mental illnesses.

The experiment suggest a part of the brain linked to addiction also plays a previously unsuspected role in illnesses characterized by chronic anxiety and social withdrawal, reported by Texas researchers in the journal Science.

A substance produced in the brain, BDNF, seems to be the culprit, controlling whether the bullied mice turned into fearful hermits or not.

Neuroscientists wanted to test the role of the brain's "reward pathway" in depression-like behavious. This brain circuitry is involved in emotional learning, and recognizing pleasure, and thus has a role in addiction. But people with major depression become almost numb, unable to experience pleasure, suggesting another role for the reward pathway.

Enter the mice, normally sociable creatures who quickly determine their pecking order, steering clear of aggressors in favour of friendlier company.

The Texas researchers subjected some small brown mice to intimidation more intense than they'd face in the wild. Each was placed for five minutes in the cage of a particularly aggressive, large white mouse, who battled the little one into a corner. Then the researchers divided the cage with a perforated, plexiglass divider for 24 hours - so the little mouse was in no physical danger, but saw and smelled the aggressor. For 10 day, each little mouse met a new bully. The bullied mice emerged drastically cowed. Four weeks later, they still fearfully withdrew from even presumably friendly little mice.

What was happening in their brains? BDNF is a chemical important for the growth and maturation of nerve cells. some antidepressants are thought to increase BDNF levels in the hippocampus, helpfully boosting neurons. But in this different brain region the so-called mesolimbic dopamine pathwya, Dr. Erid Nestler found too much BDNF was bad. The bullied mice experienced marked BDNF increases, whin in turn switched on several hundred genes located deep in the front part of the brain. That unusual gene activation paralleled the animals' social withdrawal.

Then Nestler's team injected mice with a virus that switched off BDNF production only in this one brain region, and repeated the bullying experiment. Mice lacking in BDNF didn't become cowed - they couldn't learn how to respond to this emotional threat, evidence of BDNF's role in social stress."The ability of stress to induce BDNF in this reward circuitry is probably a good thing" from an evolutionary standpoint. Nestler said. "If you're constantly subjected to something bad like being beaten up, it makes sense to avoid what's beating you up." But extreme stress can throw that normally protective system into overdrive, he explained.

That's similar to what can happen in people, when someone genetically predisposed to depression experiences a first bout after an emotionally stressful event.

Most antidepressant research has focused on overall levels of different brain chemicals, such as serotonin. But the new study suggests that's far to simplistic, since BDNF seems to have different effects in different brain regions, said Dr. Thomas Insel. "We like to think about the brain like any other organ. It's much more complicated...we need to think about changes in specific circuits, not just whether something goes up or down in the brain."

Nestler agreed, saying the work points toward potential new targets for research into depression and other mental illnesses, such as post-traumatic stress syndrome or social phobias. Among his next steps is figuring out what those BDNF-controlled genes do, to better identify those targets.

[Merika]

That was real interesting Luba. I wonder what they will do with the information?

[RandomSkater]

One of my mice finally got tired of getting beaten up by the bigger one after abour 3 months.
He totally flipped out and attacked the bigger one until I pulled them apart. He probably would've ripped his ear off if I hadn't seperated them.

[Merika]

Random.....why don't you get a male and female so they can be buddies??? LOL!

[Weiser]

Buddies huh. What makes you think they would be buddies.

Hypothetically, what if mice ruled the world and we were there pets they kept in cages.

What if YOU got locked in a cage with a fat, ugly, unpersonable man? Would you be buddies? :P

[Duke]

Our tax dollars hard at work. :roll:

[Vautrin]

Actually Duke, it is hard at work. We can't perform these experiments on humans, for obvious reasons. And we need to know what anatomical mess-ups cause which kind of behaviors. To prevent such behaviors, and perhaps even find some treatment for those problems.

Right now, a lot of knowledge of the brain is based on people who have suffered (extensive) neurological damage, so it is very hard to generalize from that.

Of course, there are a lot of limitations on this research. But at least it has prospective potential, unlike marketing research :P.

[Duke]

I'd much rather have the money wasted on these experiments put into a school system, homeless shelter, abuse councelling, cancer research or some other noble cause.

Why do we need to study the effects of stress on the brain of mice? We've got hundreds (if not thousands) of years of data with real world examples of what happens to people under stress. Better yet, the data isn't just limited to one age category, race, creed, or sex. Why not study that instead of beat on mice in a very expensive, closed environment, government controlled lab?

Honestly, I only see it as a huge waste of money when compared to the bigger picture.

[Merika]

Originally Posted by Weiser

What if YOU got locked in a cage with a fat, ugly, unpersonable man? Would you be buddies? :P

Depends on how many toys and food pellets he had on his side of the cage.

[Luba]

Originally Posted by Merika

Depends on how many toys and food pellets he had on his side of the cage.