Research indicates more than 1.5 billion people worldwide suffer from chronic pain — pain that lasts for more than six months. Respondents of a National Institute of Health Statistics survey indicated that lower back pain was the most common (27 percent), followed by severe headache or migraine pain (15 percent), neck pain (15 percent) and facial ache or pain (4 percent).

However, some people seem to cope better with pain than others, and knowing more about how these coping mechanisms work might help to develop new ways of treating these distressing symptoms.

It is well known that we have receptors in our brains that respond to natural painkilling opiates such as endorphins, but it is largely unknown how the opioid system adapts to chronic pain states. Recently, researchers at the University of Manchester demonstrated that these receptors increase in number to help cope with long-term, severe pain in arthritis sufferers.

By applying heat to the skin using a laser stimulator, Dr Christopher Brown and his colleagues at the University of Manchester showed that the more opiate receptors there are in the brain, the higher the ability to withstand the pain. The researchers used positron emission tomography (PET) imaging on 17 patients with arthritis and nine healthy controls to show the spread of the opioid receptors (OpR).

Consistent with the upregulation hypothesis, greater OpR availability was found in the striatum (including the caudate) of patients reporting higher levels of recent chronic pain, as well as regions of interest in the descending opioidergic pathway including the anterior cingulate cortex, thalamus and periaqueductal gray. The functional significance of striatal changes were clarified with respect to acute pain thresholds: data across patients and controls revealed that striatal OpR availability was related to reduced pain perception.

These findings are consistent with the view that chronic pain may upregulate OpR availability to dampen pain. Finally, patients with arthritis pain had overall less OpR availability within the striatum specifically, consistent with the greater endogenous opioid binding that would be expected in chronic pain states.

According to Brown, increasing pain medications is concerning because of possible addiction. Some patients feel anything that can reduce reliance on strong medication must be worth pursuing, and the idea of enhancing the natural opiates in the brain (such as endorphins) as a response to pain may be preferable to long-term medication with opiate drugs.

There is generally a negative and fatalistic view of chronic pain. This study shows that although the participants as a whole are more physiologically vulnerable, the whole pain system is flexible, and individuals can adaptively upregulate their resilience to pain.

It may be that some simple interventions can further enhance this natural process, and designing smart molecules or simple nondrug interventions to do a similar thing is potentially attractive.