What Animal Research Has Taught Us About Stress
These days we’re all very familiar with stress, but while we may know how it feels, we’re less sure what exactly causes it and the full range of effects it can have on the body and brain. Now, new research with mice sheds some light on the connections between stress, sleep, depression, immunity, and more.
Stress, Insomnia, and Immunity
Anyone who has laid in bed, too stressed or worried to sleep, knows there is a link between stress and insomnia. Now, researchers have identified the neural circuit responsible for stress-induced sleeplessness, and have discovered that the same circuit also affects the immune system.
In a mouse study, scientists at Stanford University found that restraint stress led to the strong activation of corticotropin-releasing hormone neurons, which promote insomnia. When the scientists interfered with the connection, the stressed mice slept peacefully.
The researchers were also able to use the same stress effect to cause changes to the immune system, including the amount of immune cells in the blood and the immune system’s responses, which could lead to new ways to boost immune system responses using the body’s natural circuitry.
Dreaming and Depression
Even mild stress can affect sleep, according to a mouse study at the University of Surrey. When mice were exposed to mild stress (by tilting their cages, wetting their bedding, or introducing unknown smells), the mice almost immediately displayed an increase in REM sleep, which is the state during which dreaming happens. Deeper non-REM sleep was unaffected.
After nine weeks of mild stress, along with an increase in REM sleep, the mice developed signs of depression, neglected self-care activities, and were less likely to be social or participate in pleasurable activities.
Sleep Quality and Susceptibility to Stress
While the Stanford and University of Surrey scientists studied the effects of stress on sleep, researchers at NYU Abu Dhabi’s Laboratory of Neural Systems and Behavior looked at the reverse effect—how abnormal sleep patterns can make people more susceptible to stress.
Using mouse models, researchers from NYUAD demonstrated how disruptions in NREM (non-rapid eye movement) sleep increases vulnerability to chronic stress, a discovery that could lead to sleep tests that boost resilience to stress in humans.
The NYUAD researchers first identified the “normal” sleep characteristics of mice, then exposed them to chronic social defeat (CSD) stress, which is known to cause chronic stress in both animals and humans.
After experiencing CSD, the mice were separated into two main types: those that displayed stress through social avoidance, and those that could handle the stress. The stressed mice showed sleep disruptions including increased switching between NREM sleep and waking periods, as well as shorter NREM sleep periods compared to the stress-resilient mice.
By comparing the pre-stress sleep patterns of the mice, scientists were able to predict their susceptibility to stress with more than 80% accuracy: Before being exposed to CSD, the stress-susceptible mice already had pre-existing abnormal sleep/wake patterns, which were exacerbated by stress.
If the same is true in humans, it shows that poor sleep patterns can make people more vulnerable to chronic stress and related mood disorders.
There’s no denying that sleep is important—it allows both the body and the brain to recharge, and it has been connected to everything from poor eating habits to chronic disease. New research with mice not only reinforces the importance of sleep, it give us important information about the connection between sleep and stress, and how we might be able to use that knowledge to both increase our resilience to stress and improve the quality of our sleep.