Editors' ChoicePain

A nap a day keeps the pain away?

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Sci. Signal.  27 Jun 2017:
Vol. 10, Issue 485, eaao1782
DOI: 10.1126/scisignal.aao1782

Getting more sleep or increasing caffeine intake during the day may relieve chronic pain better than typical pain-killers.

Chronic pain is difficult to treat, and many therapies lose their efficacy over time and are highly addictive with severe and even fatal consequences. Findings from Alexandre et al. suggest that what patients really need is a little more sleep and a big cup of coffee (or two). The authors deprived mice of sleep by keeping them stimulated in nonstressful ways—with toys and activities to mimic a human’s typical late-night behaviors. They found that mice subjected to severe acute sleep deprivation (9 or more hours) or moderate chronic sleep deprivation (6 hours for five consecutive days) were more sensitive to various noxious stimuli, an effect not seen in mice that had fragmented sleep. The widely used, over-the-counter pain reliever ibuprofen (a nonselective cyclooxygenase inhibitor) did not block the exaggerated responses to pain in sleep-deprived mice. However, caffeine (an A1 and A2A adenosine receptor antagonist that also promotes dopamine receptor expression) and the drug modafinil (which promotes dopaminergic transmission) did attenuate these responses, without showing substantial analgesic effects in well-rested mice. Furthermore, the analgesic effects of morphine were reduced by sleep deprivation. A period of normal sleep resolved the exaggerated sensory responses. Sleep deprivation and chronic pain are two rapidly emerging public health epidemics; are often coincident in patients; and now, given that sleep loss decreases the expression of dopamine receptors, are suggested to be linked through suppressed dopaminergic neurotransmission. The study shows that compounds that promote dopaminergic signaling, such as caffeine, may be better than typical pain relievers but potentially only in sleep-deprived individuals. The study also suggests that sleep deprivation in human subjects may confound the assessment of analgesic efficacy in clinical trials.

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