Washington State University researchers have found that the timing of an animal’s sleep can be just as important as how much sleeps it gets.
Ilia Karatsoreos, an assistant professor in WSU’s Department of Integrative Physiology and Neuroscience, shifted mice from their usual cycle of sleeping and waking and saw that, while they got enough sleep, it was of poorer quality. The animals also had a disrupted immune response, leaving them more open to illness.
Most sleep research focuses on the effects of sleep deprivation or the overall amount of sleep an animal needs. This is generally referred to as sleep’s homeostatic process, which is driven by sleepiness or “sleep pressure.”
The work by Karatsoreos and his colleagues–published in the journal Brain, Behavior and Immunity–is a rare look into the circadian process, a brain-driven clock that controls the rhythms of various biological processes, from digestion to blood pressure, heart rate to waking and sleeping. The cycle is found in most everything that lives more than 24 hours, including plants and single-celled organisms.
Research into the system has significant implications for modern living, write Karatsoreos and his coauthors, as “disruption of the circadian clock is nearly ubiquitous in our modern society” due to nighttime lighting, shift work, jet lag and even the blue-tinged light emitted by cell phones and tablets.
Typically, sleep researchers have a hard time studying sleep deprivation and the circadian cycle separately, as a change in one usually affects the other. However, Karatsoreos and his colleagues saw their model did not affect an animal’s total sleep, giving them a unique look into the effects on the timing of the sleeping-waking cycle.
The researchers used mice whose body clocks run at about 24 hours – much like our own – and housed them in a shorter 20-hour day. This forced their biological clocks out of sync with the light-dark cycle. After four weeks, the researchers injected the mice with lipopolysaccharide, a molecule found in bacteria that can make an animal sick without being contagious.
The researchers saw that the disrupted animals had blunted immune responses in some cases or an overactive response in others, suggesting the altered circadian cycle made them potentially less able to fight illness and more likely to get sick.
“This represents a very clear dysregulation of the system,” said Karatsoreos. “The system is not responding in the optimal manner.” Over time, he said, this could have serious consequences for an organism’s health.
“Just like you have a car that you’re running into the ground–things don’t work right but you keep driving it until it stops. That’s what could happen if you think of disruption going on for years for somebody who’s working shift work,” he said.
To his surprise, the mice on the 20-hour cycle were getting the same amount of sleep as they did on the 24-hour cycle. But the sleep wasn’t as good. The mice woke more often and the pattern of electrical activity in their brains related to restorative sleep was greatly reduced.
About this sleep research
Karatsoreos’s coauthors are doctoral student Derrick Phillips and Marina Savenkova, a postdoctoral research associate.
Funding: The work was supported by the Brain and Behavior Research Foundation and the WSU College of Veterinary Medicine.
Source: Ilia Karatsoreos – Washington State UniversityImage Source: The image is in the public domain Original Research:Abstract for “Environmental disruption of the circadian clock leads to altered sleep and immune responses in mouse” by Derrick J. Phillips, Marina I. Savenkova, and Ilia N. Karatsoreos in Brain, Behavior and Immunity. Published online July 2015 doi:10.1016/j.bbi.2014.12.008
Environmental disruption of the circadian clock leads to altered sleep and immune responses in mouse
In mammals, one of the most salient outputs of the circadian (daily) clock is the timing of the sleep–wake cycle. Modern industrialized society has led to a fundamental breakdown in the relationship between our endogenous timekeeping systems and the solar day, disrupting normal circadian rhythms. We have argued that disrupted circadian rhythms could lead to changes in allostatic load, and the capacity of organisms to respond to other environmental challenges. In this set of studies, we apply a model of circadian disruption characterized in our lab in which mice are housed in a 20 h long day, with 10 h of light and 10 h of darkness. We explored the effects of this environmental disruption on sleep patterns, to establish if this model results in marked sleep deprivation. Given the interaction between circadian, sleep, and immune systems, we further probed if our model of circadian disruption also alters the innate immune response to peripheral bacterial endotoxin challenge. Our results demonstrate that this model of circadian disruption does not lead to marked sleep deprivation, but instead affects the timing and quality of sleep. We also show that while circadian disruption does not lead to basal changes in the immune markers we explored, the immune response is affected, both in the brain and the periphery. Together, our findings further strengthen the important role of the circadian timing system in sleep regulation and immune responses, and provide evidence that disrupting the circadian clock increases vulnerability to further environmental stressors, including immunological challenges.
“Environmental disruption of the circadian clock leads to altered sleep and immune responses in mouse” by Derrick J. Phillips, Marina I. Savenkova, and Ilia N. Karatsoreos in Brain, Behavior and Immunity. Published online July 2015 doi:10.1016/j.bbi.2014.12.008