Stress Wracks Worm Nerves, Leaving Lasting Memories

Scientists stunted the puberty of male worms by starving them before they underwent sexual maturation. In the study, published in Nature and led by Oliver Hobert,PhD, researchers 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. Hobert, professor of biological sciences at Columbia University and a faculty member of the Department of Systems Biology.

The researchers’ results also suggested that these responses to stress were, in part, controlled by serotonin, a neurotransmitter associated with depression in humans.

Initially, Emily Bayer, a graduate student in the Hobert Lab and co-author of the work, stressed out immature worms when she accidentally left them unattended for a few weeks. This caused the worms to pause their normal growth and enter what scientists call a “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.

“I was totally surprised. In fact, I never thought stressing the worms out would matter,” said Bayer. 

She also found that starvation before sexual maturation caused male adult worms to act immaturely during behaviors known to be controlled by these circuits. Unlike normal adult males, the stressed worms were highly sensitive to a noxious chemical called SDS. Stressed worms swam away from SDS while normal males barely responded. The stressed worms also had problems mating. Specifically, they spent much less time in contact with hermaphrodite worms than normal males.

For the complete article, visit the National Institute of Neurological Disorders and Stroke. The Hobert Lab studies the molecular mechanisms responsible for generating the remarkable diversity of cell types found in the nervous system. Using C. elegans as a model system, researchers have revealed the regulatory mechanisms that control terminal neuronal identity and demonstrated that these mechanisms are conserved in chordates. They also used this knowledge to reprogram the identity of heterologous cell types to become specific neuron types.