Brain Response to Pain Control in People With Chronic Pain

Background: \- Researchers want to look at how the brain responds to painful stimulations. They also want to see if these responses are different in people with and without chronic pain. To test the brain s response, they will use a chemical called naloxone. Naloxone is used to treat overdoses of painkilling drugs like morphine. It may be able to block the effect of a pain-relieving cream. Researchers will apply a pain-relieving cream to a person s lower leg and look at the results of sensitivity tests with either naloxone or a placebo. This study will compare the results from people with chronic pain (like fibromyalgia) to those of people without chronic pain. Objectives: \- To look at the brain s response to pain in people with and without chronic pain. Eligibility: * Individuals at least 18 years of age who have fibromyalgia. * Healthy volunteers at least 18 years of age. Design: * This study will involve a screening visit and two testing visits. The testing visits will be about a week apart. * Participants will be screened with a physical exam and medical history. Blood and urine samples will be collected. After the screening participants will be administered several questionnaires about their personality, and their thoughts and feelings. * At the first visit, participants will try out the magnetic resonance imaging (MRI) scan before using it at the next visit. They will then have the painkilling cream applied on one part of their lower leg and a normal moisturizing cream on the other part of their lower leg. They will have heat pulses on these skin areas and rate the pain. * At the second visit, participants will have tests in the MRI scanner. The heat pulse tests will be repeated after an infusion of either naloxone or a placebo.

Different pain reducing drugs work in different ways to reduce pain. Many drugs, including morphine and codeine, reduce pain by binding to opiate receptors in the brain. Another chemical, naloxone, can block the effect of these drugs. In this study, we are looking at brain responses to a pain-relieving cream and whether naloxone blocks the effect of the cream. We will compare the results of people with chronic pain (fibromyalgia) to those of people without chronic pain. Design: The study compares MRI response to painful stimulation between people with fibromyalgia and healthy volunteers under two conditions: 1) naloxone, 2) placebo. Outcome measures: Pain ratings and pain-related MRI responses are compared between people with fibromyalgia and healthy volunteers