News in Science

Anxiety linked to brain chemical

Anxiety clue The discovery of a new biochemical pathway in the part of the brain that deals with fear offers hope for better treatment of anxiety-related disorders.

The research team, led by Dr Robert Pawlak of the Department of Cell Physiology and Pharmacology at the University of Leicester in the UK, has shown that an enzyme called neuropsin may play a key role in anxious behaviour.

"Neuropsin was known to be important in learning and memory but its role in the amygdala [the brain region involved in fear responses] has never been studied", says Pawlak.

The work is reported in this week's edition of Nature.

Neuropsin exists in the extracellular matrix, which fills the space between nerve cells, and so is ideally positioned to interact with receptors on the nerve membranes.

Pawlak and his team compared normal mice with "knock-out" mice which were unable to make neuropsin. Both types of mice were restrained from moving for a while, an experience which put them under stress. The neuropsin levels in the normal mice rose after stress by 50%.

The team went on to demonstrate a cascade of events whereby the raised neuropsin levels eventually led to a 21-fold increase in the activity of a gene which is thought to be important in post-traumatic stress disorder (PTSD), anxiety and depression.

After being stressed, the mice were tested to see whether they were anxious by placing them in a maze which had darkly-lit and brightly-lit regions.

The normal mice had been made anxious by their experience and were reluctant to enter the bright regions of the maze.

By contrast, the knock-out mice appeared to be relaxed, readily entering bright parts of the maze. Their lack of neuropsin seemed to fit with less anxiety.

Pawlak is excited about the findings. "We know that all members of the neuropsin pathway are present in the human brain", he says, "so they may play a similar role in humans".

However, Professor Pankaj Sah, an expert in the amygdala from the Queensland Brain Institute, has some reservations.

He points out that knock-out mice are abnormal in many ways, which could give misleading results, and that only one way of measuring anxiety was used. He says more research is needed.

"It would be great to genotype people who have anxiety disorders such as PTSD and see what RNAs are being expressed, to determine if there is a difference in their neuropsin", says Sah.

"Or you could use tissue from brain banks of people with high anxiety and see if their neuropsin levels were high."