Stress Wracks Worm Nerves, Leaving Lasting Memories

Scientists stunted the puberty of male worms by starving them before they underwent sexual maturation. In a study funded by NINDS, the scientists suggested that stress from starvation even days before sexual maturation prevented normal changes in the wiring patterns of key neuronal circuits, which caused adult male worms to act immature.

“We found that environmental stress can permanently and profoundly impact the connectivity of a developing nervous system,” said Dr. Oliver Hobert of Columbia University, a senior author of the study published in Nature.

Hobert’s lab studies the nervous system of tiny see-through worms called Caenorhabditis elegans, or C. elegans. Previously, scientists in his lab showed how sexual maturation genetically reprograms and reshapes the wiring patterns of some neuronal circuits in male worms, making them different from their hermaphrodite mating partners.

In this study, Emily Bayer, a graduate student in the lab, discovered that exposure to stress, specifically starvation, before maturation can interrupt the rewiring program in males leaving the adult worms with immature circuits. Her results also suggested that these responses to stress were, in part, controlled by serotonin, a neurotransmitter associated with depression in humans.

“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 Dr. Jill Morris, NINDS program director.

Initially, Bayer stressed out immature worms when she accidentally left some animals unattended for a few weeks. This caused the worms to pause their normal growth and enter what scientists call a “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,” said Hobert. “This temporary freeze in the growth process is the dauer state.”

Eventually, Bayer returned the worms to their normal environment and let them grow into adults. After examining the nervous systems of stressed worms, she noticed something unusual. Normally, some of the neuronal connections in the males’ tails are eliminated, or pruned, during sexual maturation. Instead, she found that immature connections in the stressed worms remained.

Follow-up experiments suggested that this was strictly caused by starvation and no other forms of stress—such as heat—could have caused the dauer state.