A study of a microscopic roundworm is lending insight into the phenomenon of sleepiness that often accompanies sickness. Researchers at the University of Pennsylvania’s Perelman School of Medicine found that a single nerve cell called ALA coordinates an organism-wide response to sickness in worms.

The study is published in eLife.

When cells undergo stress during sickness, organisms can experience sleepiness, which promotes sleep to recover from the stress.  The study showed that for the worm, the sleepiness comes from a release of FLP-13 and other neuropeptides (chemicals which send signals between brain neurons) from the ALA neuron.

“Sleep is vitally important in helping both people and animals to recover during sickness,” said senior author David M. Raizen, an associate professor of neurology and a member of the Center for Sleep and Circadian Neurobiology. “Similar signaling may operate in humans and other animals to regulate sleep during sickness. These findings create a launching pad toward future research into the mechanisms for illness-induced sleepiness in humans and other organisms.”

The research showed that FLP-13 causes sleep by reducing activity in the nervous system cells which can help keep the organism awake. By examining genetic mutations, the researchers were able to determine which genes cause the worms to fall asleep when FLP-13 is released. Because worms that lacked the receptor protein DMSR-1 on cell surfaces did not become sleepy in response to FLP-13, they deduced that DMSR-1 is essential for FLP-13 to trigger sleep.

Next, the researchers will work to determine whether illness-induced sleepiness in humans and other mammals has the same trigger. This information could help in the development of drugs to treat human fatigue associated with sickness and other conditions.