Being bullied may dramatically affect sleep

August 10, 2017
Credit: CC0 Public Domain

New research from McLean Hospital neuroscientists shows in an animal model that being bullied can have long-term, dramatic effects on sleep and other circadian rhythm-related functions, symptoms that are characteristic of clinical depression and other stress-induced mental illnesses. The researchers, however, also found that it may be possible to mitigate these effects with the use of an experimental class of drugs that can block stress.

"While our study found that some stress-related effects on circadian rhythms are short-lived, others are long-lasting," said William Carlezon, PhD, chief of the Division of Basic Neuroscience and director of the Behavioral Genetics Laboratory at McLean Hospital and senior author of the study. "Identifying these changes and understanding their meaning is an important step in developing methods to counter the long-lasting effects of traumatic experiences on mental health."

Stress is known to trigger psychiatric illnesses, including depression and PTSD, and sleep is frequently affected in these conditions. Some people with stress disorders sleep less than normal, while others sleep more than normal or have more frequent bouts of sleep and wakefulness.

To demonstrate the effects of bullying, the researchers used an simulating the physical and emotional stressors involved in human bullying—chronic social defeat stress.

For this procedure, a smaller, younger mouse is paired with a larger, older, and more aggressive mouse. When the smaller mouse is placed into the home cage of the larger mouse, the larger mouse instinctively acts to protect its territory.

In a typical interaction lasting several minutes, the larger mouse chases the smaller mouse, displaying aggressive behavior and emitting warning calls. The interaction ends when the larger mouse pins the smaller mouse to the floor or against a cage wall, establishing dominance by the larger mouse and submission by the smaller mouse.

The are then separated and a barrier is placed between them, dividing the home cage in half. A clear and perforated barrier is used, enabling the mice to see, smell, and hear each other, but preventing physical interactions. The mice remain in this arrangement, with the smaller mouse living under threat from the larger mouse, for the rest of the day. This process is repeated for 10 consecutive days, with a new aggressor introduced each day.

To collect data continuously and accurately, researchers outfitted the smaller mice with micro-transmitters that are akin to activity trackers used by people to monitor their exercise, heart rate, and sleep. These mice micro-transmitters collected sleep, muscle activity, and body temperature data, which revealed that the smaller mice experienced progressive changes in sleep patterns, with all phases of the sleep-wake cycle being affected. The largest effect was on the number of times the mice went in and out of a sleep phase called paradoxical sleep, which resembles REM (rapid eye movement) sleep in humans, when dreams occur and memories are strengthened. Bullied mice showed many more bouts of paradoxical sleep, resembling the type of sleep disruptions often seen in people with depression. Bullied mice also showed a flattening of body temperature fluctuations, which is also an seen in people with depression.

"Both the sleep and body temperature changes persisted in the smaller mice after they were removed from the physically and emotionally threatening environment, suggesting that they had developed symptoms that look very much like those seen in people with long-term depression," said Carlezon. "These effects were reduced, however, in terms of both intensity and duration, if the mice had been treated with a kappa-opioid receptor antagonist, a drug that blocks the activity of one of the brain's own opioid systems."

Carlezon explained that these findings not only reveal what traumatic experiences can do to individuals who experience them, but also that we may someday be able to do something to reduce the severity of their effects.

"This study exemplifies how measuring the same types of endpoints in laboratory animals and humans might hasten the pace of advances in psychiatry research. If we can knock out stress with new treatments, we might be able to prevent some forms of mental illness."

The detailed findings of this study are available in the August 9, 2017 issue of the Journal of Neuroscience.

Explore further: Mice offer a window into sleep's role in memory

Related Stories

Mice offer a window into sleep's role in memory

March 24, 2017
Sleep provides essential support for learning and memory, but scientists do not fully understand how that process works on a molecular level. What happens to synapses, the connections between neurons, during sleep that helps ...

Mouse study shows REM sleep selectively prunes and maintains new synapses

January 27, 2017
(Medical Xpress)—A small team of researchers with affiliations to the New York University School of Medicine and Peking University has found evidence of pruning and maintenance of synapses during REM sleep. In their paper ...

How sleep deprivation affects memory-making in the brain

April 7, 2017
Scientists have known that a lack of sleep can interfere with the ability to learn and make memories. Now, a group of University of Michigan researchers have found how sleep deprivation affects memory-making in the brain.

Calcium controls sleep duration in mice

March 17, 2016
University of Tokyo and RIKEN researchers have identified seven genes responsible for causing mice to stay awake or fall asleep based on a theoretical model of sleep and on experiments using 21 different genetically-modified ...

Lighting color affects sleep and wakefulness

June 8, 2016
A research team from Oxford University have shown how different colours of light could affect our ability to sleep.

Researchers identify first two genes regulating sleep in mice using genetic screening

November 2, 2016
Researchers have identified the first two core genes that regulate the amount of deep sleep and dreaming, a key development they believe will lead to the discovery of a network of related genes controlling sleep.

Recommended for you

Researchers find monkey brain structure that decides if viewed objects are new or unidentified

August 18, 2017
A team of researchers working at the University of Tokyo School of Medicine has found what they believe is the part of the monkey brain that decides if something that is being viewed is recognizable. In their paper published ...

Artificial neural networks decode brain activity during performed and imagined movements

August 18, 2017
Artificial intelligence has far outpaced human intelligence in certain tasks. Several groups from the Freiburg excellence cluster BrainLinks-BrainTools led by neuroscientist private lecturer Dr. Tonio Ball are showing how ...

Study of nervous system cells can help to understand degenerative diseases

August 18, 2017
The results of a new study show that many of the genes expressed by microglia differ between humans and mice, which are frequently used as animal models in research on Alzheimer's disease and other neurodegenerative disorders.

How whip-like cell appendages promote bodily fluid flow

August 18, 2017
Researchers at Nagoya University have identified a molecule that enables cell appendages called cilia to beat in a coordinated way to drive the flow of fluid around the brain; this prevents the accumulation of this fluid, ...

Researchers make surprising discovery about how neurons talk to each other

August 17, 2017
Researchers at the University of Pittsburgh have uncovered the mechanism by which neurons keep up with the demands of repeatedly sending signals to other neurons. The new findings, made in fruit flies and mice, challenge ...

Neurons involved in learning, memory preservation less stable, more flexible than once thought

August 17, 2017
The human brain has a region of cells responsible for linking sensory cues to actions and behaviors and cataloging the link as a memory. Cells that form these links have been deemed highly stable and fixed.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.