How It Works

Answer to fear found in parasitic worms

Wasps, needles, heights, blood, spiders – ask a few of your friends about their greatest phobias and you will get a variety of different answers. But the human brain is so complex that getting to the bottom of the mechanisms behind fear and anxiety is a difficult feat. Prescribing clinical anti-anxiety medication has shown success but the results to their efficacy is mixed.

But new clues about the mechanisms have been revealed after a team of scientists from the Salk Institute have used parasitic intestinal worms in their studies. The worms have been analysed by exposing the creepy crawlies to chemicals secreted by their natural predator – another worm. The researchers have discovered a fear-like response that resembles human anxiety, and may mean that new drugs to treat conditions like PTSD and panic disorders can be tested and refined.

Sreekanth Chalasani, associate professor in Salk’s Molecular Neurobiology Laboratory and senior author of the paper, published in Nature Communications, has commented in a press release “The idea has been that if you could figure out which underlying signals in the brain are related to fear and anxiety, you could develop better drugs to block them.”

The test subject in the study is a microscopic worm, Caenorhabditis elegans. and their natural predator is Pristionchus pacificus. The paper reports that in response to detecting chemicals secreted from its predator the worm will rapidly change direction and crawl away.

“For years, we thought that only advanced brains like those of mammals would have this complex reaction,” Chalasani says. “But our study is showing that a simple animal expresses something very much like fear.”

The experiment soaked C. elegans in the fear-inducing chemicals for 30 minutes and found that the worms failed to lay eggs (an indicator of both acute stress and longer-term anxiety) for an entire hour after being removed from the solution. Upon investigation, the team found that the signalling-pathways activated in the worm’s simple network of 302 neurons, are similar to the mechanisms when a more complex animal experiences fear. The anxiety response was not seen after soaking the worms in a Zoloft solution suggesting that our species may be using ancient fear mechanisms in response to stress. “Our findings suggest that fear and anxiety are ancient and evolved much earlier than we originally thought. The pathways, nerves, circuits and genes that we’ll now be able to study in the worm should inform us about this process in humans.”

The paper’s other authors were Zheng Liu, Maro J. Kariya, Christopher D. Chute, Sarah G. Leinwand, Ada Tong, and Kevin P. Curran of Salk; Neelanjan Bose and Frank C. Schroeder of Cornell University; and Jagan Srinivasan of Worcester Polytechnic Institute.