What Causes Sleepiness When Ill?

Every time a human or an animal is sick, they become fatigued and sleepy. Researchers are using a microscopic roundworm that’s providing an explanation of how that all occurs. According to a study from the researchers at the Perelman School of Medicine at the University of Pennsylvania, they reveal, by a study published in eLife, the mechanism for this sleepiness.

A worm’s simple nervous system has shown how a single nerve cell named ALA coordinates an organism-wide response to sickness. The cells are under stress during sickness and organisms experience sleepiness to promote sleep and recover from the cellular stress. This sleepiness is caused by release from the ALA neuron of FLP-13 and other neuropeptides in the worm. This is a group of chemicals that send signals between brain neurons.

It is vitally important to get sleep in helping both people and animals to recover during any sickness, according to author David M Raizen, MD, PhD, an associate professor of neurology and a member of the Center for Sleep and Circadian Neurobiology. There may be similar signaling operating in humans and other animals to regular the sleep during sickness. This creates a launching pad towards future research into the mechanisms for illness-induced sleepiness in humans and other organisms.

This reveals that FLP-13 causes sleep by turning down the activity in the nervous system cells that help keep an organism awake. The researchers, to determine which genes cause the worms to fall asleep when FLP-13 is released, examined genetic mutations. The worms with mutations that cause them to lack a receptor protein called DMSR-1 on cell surfaces do not become sleepy in response to FLP-13. This confirms that DMSR-1 is essential for FLP-13 to trigger sleep.

The experiments next to be done will target if illness-induced sleepiness in humans and other mammals is triggered by a similar mechanism. This may be a critical step towards developing drugs that will trigger via a similar mechanism. This could be a critical step towards developing drugs to treat human fatigue that is associated with sickness and other conditions.

Funding was provided by the National Institutes of Health, the European Research Council and the Fonds Wetenschappelijk Onderzoek.

I have always told our patients, when you feel like taking a nap, please do so. The body is trying to tell you it needs time to heal and needs you to get your mind away from commanding everything else. Your body has been good to you, now its time to be good to your body.

–Dr Fredda Branyon