Osteoarthritis: Interactions between endogenous brain opioids and the physiological and psychological responses to pain.

About 15% of the population have health problems due to arthritis and other associated conditions. The most common type of arthritis is osteoarthritis. The main reason why people with osteoarthritis go to see a doctor is pain. Pain is also the main reason why people with osteoarthritis lose their mobility. However the type of treatments available for people with osteoarthritis are very limited. Our research group has carried out studies that have shown that pain from osteoarthritis has an emotional effect on the brain that affects how pain is felt. This emotional effect could make a big difference to how patients respond to treatment or surgery. By reducing the effects of these emotions we could reduce how unpleasant the pain feels. This could also help to keep more people mobile. Our research aims to investigate how emotions such as anxiety and distress which affects how we feel pain, are altered by the natural painkillers made by the brain (opiates). We would like to approach people with osteoarthritis and ask them to take part in our study. Specifically, we would like to test a variety of people with different levels of anxiety and distress. We will make use of techniques that can produce images of the brain to measure the naturally occurring brain opiates, and how they affect how we expect (anticipate) and feel (give attention to) pain. These studies will help us explain how different people experience pain and why they respond differently to treatments. In the long term, they will also help us understand how the brains own painkillers work, and how we can improve on existing treatments for pain from osteoarthritis and also develop new therapies.

Pain is the main cause of disability in patients with osteoarthritis (OA). However, there is a highly variable relationship between joint damage and the corresponding pain experience. We have established the brain structures that process pain in OA, and showed a greater response in areas concerned with affective processing such as the anterior cingulate cortex, prefrontal cortex, amygdala, hypothalamus and anterior insula.
These area are known to show changes in mu-opioid receptor availability in response to pain stimulation. We propose to study the effects of endogenous opioids (EO?s) in reducing pain processing within these brain areas. We will measure changes in opioid receptor binding in the brain to determine the brains production of EO?s in response to pain. We will assess: 1/ whether this is reduced in OA patients with psychological distress and 2/ if this correlates with altered ability to anticipate pain and switch attention away from the unpleasantness of pain. This will provide a step-change in our understanding of the physiology of pain perception in OA. It will facilitate more rational approaches to new therapies and existing treatments.