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Chronic sleep loss can increase sensitivity to pain, according to a new study conducted on laboratory mice from researchers at Boston Children's Hospital and Beth Israel Deaconess Medical Center (BIDMC).

The research, published in Nature Medicine, also suggested that getting more sleep or taking a medication that promotes wakefulness, such as caffeine, can provide relief for chronic pain sufferers. Interestingly, both of these methods were more effective than standard analgesics in laboratory mice.

For the study, researchers measured the effects of sleep loss on sensitivity to painful and non-painful stimuli. The researchers began by measuring normal sleep cycles for each laboratory mouse in the study. This gave them exact baseline data on how much each rodent sleep and what their sensory sensitivity was.

While many sleep studies force mice to stay awake by walking on treadmills, the researchers tried a different tactic. Each mouse was provided with toys and activities at the time when they usually went to sleep, extending the wake period.

To keep the mice awake without stressing the rodents out, the researchers provided the mice with new toys as interest flagged in an old one. These toys included nesting materials, like a wipe or a cotton ball.

(If this sounds familiar, it's because it's very similar to what people do when they stay up late playing games on their phone, watching late-night television, or to finish that last chapter).

With this method, the researchers were able to keep groups of six - 12 mice awake for as long as 12 hours at a time or for six hours over a consecutive five day period.

The researchers then measured pain sensitivity in these mice. The rodents were exposed to controlled amounts of heat, cold, pressure, capsacin, or loud noises. The sleep-deprived animals were significantly more sensitive to pain.

"We found that repeated moderate sleep loss (5 consecutive days) is sufficient to cause a buildup of sleep debt and pain hypersensitivity in mice, while their response to other non-painful stimulations were not affected," study authors, pain physiologist Alban Latremoliere, Ph.D., of Boston Children's and sleep physiologist Chloe Alexandre, Ph.D., of BIDMC, said to ALN.

Interestingly, standard pain medications, like ibuprofen and morphine, did little to block sleep-deprived pain hypersensitivity. However, drugs used to promote wakefulness, like caffeine and modafinil, blocked pain hypersensitivity caused by sleep loss.

This has led the researchers to suggest that patients in chronic pain may benefit from better sleep habits coupled with daytime alertness-promoting agents, rather than just taking painkillers.

"One immediate implication for the general population is that the deleterious effects of even a moderate sleep deprivation can accumulate over time so that by the end of the week we are oversensitive to pain and less likely to get relieve from pain killers. For patients suffering from chronic pain, our data suggest that finding strategies to promote sleep could help break the vicious cycle by reducing the sleep loss-induced pain hypersensitivity and restore the efficacy of some painkillers," the researchers concluded.

"We would like to thank the NIH for funding our studies. They have been extremely supportive of our research from the start and we are extremely grateful they gave us a chance to start this new line of research."

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