University of IowaIt is known that breathing carbon dioxide can trigger panic attacks. However the biological reason for this effect appears to have not been understood. A latest study by University of Iowa scientists has found that carbon dioxide seems to raise brain acidity. Apparently, this in turn activates a brain protein that plays a crucial role in fear and anxiety behavior.

During the study, the authors were noted to have focused on a brain protein known as acid-sensing ion channel 1a (ASIC1a). This protein seems to be in plentiful in the amygdala, the region deep inside the brain that processes fear signals and directs fear behavior. The UI team earlier found that blocking or removing ASIC1a may possibly decrease inherent fear and alter fear memory in mice.

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

The findings of the study put forward novel possibilities for understanding the biological basis of panic and anxiety disorders in general. Moreover, it could perhaps suggest new approaches for treating these conditions. Besides assisting in elucidating why breathing carbon dioxide can trigger panic attacks, the study also suggests a new role for the amygdala as a sensor that could be able to 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 chemical signals — carbon dioxide and acidity (low pH) — that are known to trigger panic attacks in susceptible individuals,” says Wemmie.

Carbon dioxide inhalation may perhaps be fatal at high doses. The study suggests that evolution could have provided humans with a very important ability to detect and respond rapidly to carbon dioxide. Apparently, this can be done via 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 latest study also revealed that inhaled carbon dioxide seems to increase brain acidity and evoke fear behavior in mice by activating ASIC1a in the amygdala. Fear memory is also known to be improved when carbon dioxide activates the protein. On the contrary, the team including first author Adam Ziemann, M.D., Ph.D., found that making brain tissue less acidic i.e. raising brain pH seemed to have blunted fear behavior created by carbon dioxide and reduced learned fear.

Wemmie further said that, “It’s been suggested that controlling breathing with breath exercises could have anti-anxiety effects. 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.”

Presently, the authors are believed to be investigating whether ASIC1a abnormalities add to panic and anxiety disorder in people or to carbon dioxide sensitivity in patients with panic disorder. If ASIC1a plays similar role in people as the studies suggest it does in mice, then drugs that target ASIC channels or strategies that alter brain acidity may be potential in treating a wide range of panic and anxiety disorders.

The findings of the study have been published in the journal, Cell.