Stress on Worms Could Give Insight into Early Human Brain Development

Neurologists discovered how stressing out a worm rewired its nervous system -- making adult worms act like juveniles.

Worms and humans might have more in common neurologically than researchers ever thought, particularly when it comes to stress. A recent study from the National Institute of Health put male worms under duress during their puberty to study how that stress affected their neurological wiring.

They discovered stress from developmental trauma plays a role in how neurons function.

"We found that environmental stress can permanently and profoundly impact the connectivity of a developing nervous system," said Oliver Hobert, Ph.D., professor of biological sciences at Columbia University in New York City. Holbert served as a senior author of the study published in Nature.

Stressing out and sexually starving worms

Hobert and graduate student Emily Bayer studied the nervous systems of Caenorhabditis elegans, or C. elegan worms. Hobert’s lab is familiar with the tiny see-through worms; previous research teams with Hobert's lab showed how sexual maturation in worms could reshape their neural circuits in male worms. 

This new research looked at the opposite effect. 

Graduate student Emily Bayer discovered that exposure to stress -- namely starvation -- before hitting sexual maturity interrupts the brain's wiring processes. Bayer also suggested in her research that it's controlled in part by serotonin, a neurotransmitter most humans associate with depression. 

"I was totally surprised. In fact, I never thought stressing the worms out would matter," said Bayer. "It wasn't until I saw differences in their circuits that I realized that stress could remap their wiring diagrams."

Bayer said the experiment was slightly accidental. She left several of the animals unattended for a few weeks. This led to the worms to completely pause in their developmental state and enter something called the "dauer state." 

"Basically, if immature worms sense stress of any kind they can temporarily halt their normal growth for months and then restart it when the stress passes. This temporary freeze in the growth process is the dauer state," said Hobert.

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Bayer put the worms back in their normal environment and they grew to full adulthood. But she noticed something unusual as she observed their nervous systems. 

Typically, the neuronal connections in a male's tail go away during sexual maturation in a process called "pruning." However, Bayer noticed that unfinished connections in the stressed worms were still there. She also noticed that pruning is controlled by the opposite effects of both serotonin and octopamine -- the "fight or flight" neurotransmitter. Stressed worms had problems mating; they spent less time in contact with the hermaphrodite worms than the mature males.

"Exploring how genes and the environment shape the nervous system is critical to understanding how circuits break down to cause a variety of neurological disorders," said Jill Morris, Ph.D., program director at the NIH's National Institute of Neurological Disorders and Stroke (NINDS).

Does stress affect worms like it does humans?

There’s plenty of research in child development about the effects of childhood trauma on a person’s upbringing and general attitude toward life. But does this new research suggest the human nervous system undergoes similar developmental changes?

The researchers say not quite yet.

"That's a tricky question. Right now, it's very hard to pin down these kinds of differences in humans and other animals with large complicated nervous systems," said Dr. Hobert. "Nevertheless, worms are so simple and easy to study that we can provide detailed proofs of principals that may guide nervous systems great and small."

Hobert and his team hope to use the results from the project to further explore how genes are affected by life experiences.