There is nothing worse than not getting any sleep. Everything feels more irritating, people become harder to tolerate, and it can be hard to do the most basic of tasks. This is further demonstrated by new research from Boston Children’s Hospital and Beth Israel Deaconess Medical Center (BIDMC), which shows that chronic sleep loss increases pain sensitivity. Fortunately, they found that this effect can be mitigated by the caffeine found in your morning coffee.
The researchers of the study wanted to precisely measure the effects of acute and chronic loss of sleep on sleeplessness and its effect on both painful and non-painful stimuli. They carried out their study on mice models using common pain medications such as ibuprofen and morphine as well as agents that promote wakefulness such as caffeine and modafinil.
The team measured normal sleep cycles using an electroencephalogram (EEG) on mouse brains in combination with an electromyogram (EMG) to test the electric activity of muscle tissue in order to get accurate baseline data to compare their results to. They utilized less conventional ways to keep the mice awake, leading them to become chronically sleep deprived but in a less stressful manner, which is much more similar to how sleep deprivation occurs in humans. They achieved this by providing the mice with toys and activities at the time they usually went to sleep, thereby extending their wake period.
“This is similar to what most of us do when we stay awake a little bit too much watching late-night TV each weekday,” says Alexandre, who works in the lab of Thomas Scammell at BIDMC.
Alexandre was able to keep six to 12 mice awake for as long as 12 hours in one session and six hours for five consecutive days. They monitored sleepiness and stress hormones while testing for pain throughout the duration of the test. Pain sensitivity was tested in a blind fashion by exposing mice to controlled amounts of heat, cold, pressure, or capsaicin—the substance in chili peppers that gives off the heat sensation. They then measured how long it took for the mice to move away from the stimuli in discomfort. Non-painful stimuli were also tested by startling the mice with sudden loud sounds.
“We found that five consecutive days of moderate sleep deprivation can significantly exacerbate pain sensitivity over time in otherwise healthy mice. The response was specific to pain, and was not due to a state of general hyperexcitability to any stimuli,” said sleep physiologist Chloe Alexandre of BIDMC.
When attempting to relieve the sleep loss-induced pain sensitivity, common analgesics such as ibuprofen and morphine did nothing to relieve the hypersensitivity, suggesting that pain relief drugs would have to be consumed in excessive doses to compensate for sleep loss. When using drugs that promote wakefulness, however, such as caffeine and modafinil, a successful block of pain hypersensitivity was observed for both acute and chronic sleep loss—the caffeine essentially acted like an analgesic.
“Many patients with chronic pain suffer from poor sleep and daytime fatigue, and some pain medications themselves can contribute to these co-morbidities. This study suggests a novel approach to pain management that would be relatively easy to implement in clinical care. Clinical research is needed to understand what sleep duration is required and to test the efficacy of wake-promoting medications in chronic pain patients,” notes Kiran Maski, a specialist in sleep disorders at Boston Children’s Hospital.
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