Being bullied may dramatically affect sleep

August 10, 2017, McLean Hospital
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

Neuroimaging study reveals 'hot spot' for cue-reactivity in substance-dependent population

November 20, 2018
When patients with dependence on alcohol, cocaine or nicotine are shown drug cues, or images related to the substance, an area of their brain known as the medial prefrontal cortex (mPFC) shows increased activity, report investigators ...

When storing memories, brain prioritizes those experiences that are most rewarding

November 20, 2018
The brain's ability to preserve memories lies at the heart of our basic human experience. But how does the brain's mechanism for memory make sure we remember the most significant events and not clog our minds with superfluous ...

To predict the future, the brain has two clocks

November 20, 2018
That moment when you step on the gas pedal a split second before the light changes, or when you tap your toes even before the first piano note of Camila Cabello's "Havana" is struck. That's anticipatory timing.

Researchers hope to be able to replace dysfunctional brain cells

November 20, 2018
A new study by researchers at Karolinska Institutet supports the theory that replacement of dysfunctional immune cells in the brain has therapeutic potential for neurodegenerative diseases like ALS and Alzheimer's disease. ...

White matter pathway and individual variability in human stereoacuity

November 20, 2018
Researchers in the Center for Information and Neural Networks (CiNet), the National Institute of Information and Communications Technology and Osaka University have identified a human white matter pathway associated with ...

Can genetic therapy help kids with Angelman syndrome overcome seizures?

November 20, 2018
Angelman syndrome is a genetic disease with no cure. Children grow up with severe intellectual disabilities and a range of other problems, arguably the worst of which are epileptic seizures. Now scientists at the UNC School ...

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.