Pain from nerve injury causes distinct changes in mice’s sleep patterns that aren’t seen with other types of pain. The finding suggests that sleep disturbances could be used to measure and diagnose such neuropathic pain.
Quantifying pain is notoriously difficult. Most methods are subjective, such as asking patients to rate their discomfort on a scale of 1 to 10. In animals, the task is even trickier, further complicating pain research and the development of new treatments. One solution may be looking at sleep disturbances – a common complaint for people with chronic pain.
at Johns Hopkins University in Maryland and his colleagues tracked the sleep patterns of about 50 mice one week before and at least seven weeks after permanent sciatic nerve injury in their legs. The team monitored the mice’s brain activity using electrodes, noting when they entered the different phases of sleep: rapid eye movement (REM) and non-REM. In people, dreaming occurs during REM sleep and brain activity is higher. Non-REM sleep includes three stages: falling asleep, light sleep and deep sleep.
Advertisement
After nerve damage, the mice had a greater number of non-REM sleep episodes, but they didn’t last as long – indicating that the mice woke up more frequently during this type of sleep. The awakenings were very brief, averaging 2 to 6 seconds. The sleep fragmentation was also consistent over time, with mice still exhibiting non-REM sleep disruptions up to six months after injury. Their REM sleep was unchanged.
Mice with other types of pain, such as inflammatory or post-operative pain, didn’t experience the same disruption in non-REM sleep, suggesting that it is characteristic of neuropathic pain.
“We are still working to find and test different types of chronic pain models and their sleep problems, but I would expect that different pain symptoms are causing specific sleep disturbances,” says Latremoliere, who presented the work at the Advances in Pain conference in New York City on 4 May.
Tracking sleep could also be used to diagnose various types of pain and determine appropriate treatments. For example, a 10-milligram dose of gabapentin, a drug for neuropathic pain, restored sleep in mice and reduced pain sensitivity. But a 30-milligram dose increased sleep too much, suggesting a sedative effect. Some drugs didn’t work at all: they didn’t reduce pain sensitivity or restore sleep. Morphine actually worsened sleep fragmentation.
“Pain is not a simple thing. Different chronic pain pathologies can be distinct diseases states,” says Latremoliere. “Developing better ways of diagnosing pain is what will allow clinicians to prescribe the best and most efficient drug right away.”
Sign up to our free Health Check newsletter for a round-up of all the health and fitness news you need to know, every Saturday
