Study sheds light on brain's fear processing center

Nov 25, 2009

Breathing carbon dioxide can trigger panic attacks, but the biological reason for this effect has not been understood. A new study by University of Iowa researchers shows that carbon dioxide increases brain acidity, which in turn activates a brain protein that plays an important role in fear and anxiety behavior.

The study, published in the Nov. 25 issue of the journal Cell, offers new possibilities for understanding the biological basis of and disorders in general and may suggest new approaches for treating these conditions.

The researchers focused on a protein known as acid-sensing 1a (ASIC1a). This protein is abundant in the -- the region deep in the brain that processes signals and directs fear behavior. The UI team previously found that blocking or removing ASIC1a reduces innate fear and alters fear memory in mice.

"As long ago as 1918, scientists learned that triggers abnormal responses in patients with , but our study provides the first molecular evidence for a mechanism that explains how carbon dioxide can trigger fear and anxiety," said John Wemmie, M.D., Ph.D., associate professor of psychiatry and neurosurgery at the UI Carver College of Medicine and a staff physician and researcher at the Iowa City Veterans Affairs Medical Center. "The findings are a foundation for saying that ASIC proteins in the amygdala might play a key role in sensitivity to carbon dioxide."

In addition to helping explain why breathing carbon dioxide can trigger panic attacks, the study also suggests a new role for the amygdala as a sensor that can detect certain fear signals for itself.

"This is a new finding that the amygdala, which is considered the brain's computer processor for fear, can also function as a sensor for detecting -- carbon dioxide and acidity (low pH) -- that are known to trigger panic attacks in susceptible individuals," Wemmie said.

Carbon dioxide inhalation can be deadly at high doses. The study suggests that evolution may have provided humans with a vital ability to detect and respond rapidly to carbon dioxide by placing within the same brain region the ability to detect the threat posed by carbon dioxide and the ability to initiate a "fight or flight" response.

The new study shows that inhaled carbon dioxide increases brain acidity and evokes fear behavior in mice by activating ASIC1a in the amygdala. Fear memory is also enhanced when carbon dioxide activates the protein.

Conversely, the study team, including first author Adam Ziemann, M.D., Ph.D., found that making brain tissue less acidic (raising brain pH) blunted fear behavior produced by carbon dioxide and reduced learned fear.

"It's been suggested that controlling breathing with breath exercises could have anti-anxiety effects," Wemmie said. "Our results make me wonder if some of those breath exercises to control fear and anxiety might be acting by inhibiting the ASIC channels in the amygdala by raising the pH."

Wemmie and his colleagues are now investigating whether ASIC1a abnormalities contribute to panic and anxiety disorder in people or to carbon dioxide sensitivity in patients with panic disorder.

If ASIC1a plays the same role in people as the studies suggest it does in mice, then drugs that target ASIC channels or strategies that alter brain acidity could hold promise for treating a wide range of panic and anxiety disorders.

Source: University of Iowa (news : web)

Explore further: Growing a blood vessel in a week

add to favorites email to friend print save as pdf

Related Stories

Altering a protein makes mice less fearful

Aug 01, 2007

A University of Iowa study shows that loss or chemical inhibition of a protein, known as acid sensing ion channel protein (ASIC1a), reduces innate fear behavior in lab animals, making normally timid mice relatively fearless. ...

Study suggests new target for treatment of depression

Apr 28, 2009

A brain protein involved in fear behavior and anxiety may represent a new target for depression therapies, according to a study by researchers at the University of Iowa and the Iowa City Veterans Affairs Medical Center. The ...

Carbon dioxide triggers inborn distress

Oct 03, 2007

PLoS ONE publishes a study showing that inhalation of carbon dioxide (CO2) triggers emotional distress and a panic response in healthy individuals. The findings of the study posit panic as an inborn survival-oriented response. ...

Research identifies brain cells related to fear

Jul 11, 2008

The National Institute of Mental Health estimates that in any given year, about 40 million adults (18 or older) will suffer from some form of anxiety disorder, including debilitating conditions such as phobias, panic dis ...

Recommended for you

Growing a blood vessel in a week

Oct 24, 2014

The technology for creating new tissues from stem cells has taken a giant leap forward. Three tablespoons of blood are all that is needed to grow a brand new blood vessel in just seven days. This is shown ...

Testing time for stem cells

Oct 24, 2014

DefiniGEN is one of the first commercial opportunities to arise from Cambridge's expertise in stem cell research. Here, we look at some of the fundamental research that enables it to supply liver and pancreatic ...

Team finds key signaling pathway in cause of preeclampsia

Oct 23, 2014

A team of researchers led by a Wayne State University School of Medicine associate professor of obstetrics and gynecology has published findings that provide novel insight into the cause of preeclampsia, the leading cause ...

Rapid test to diagnose severe sepsis

Oct 23, 2014

A new test, developed by University of British Columbia researchers, could help physicians predict within an hour if a patient will develop severe sepsis so they can begin treatment immediately.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

barakn
3 / 5 (2) Nov 26, 2009
So much for breathing into a brown paper bag.