Why Opioids Can't Always Reduce Chronic Pain ??

While #opioids have been in use in North America since at least the time of the Civil War, we still don’t know everything about how they work. New research has indicated that #chronic pain alters receptors in the brain that attach to opioids. This alteration may reduce the effectiveness of opioids. The study also provided insight into how opioids can cause #depression. We know that people with chronic pain have reduced availability of opioid receptors — the molecules opioid drugs bind to — in the #brain.
An imaging technique that allows researchers to see disease or injury, #positron emission tomography (PET), was performed on cross-sections of rat brains. The #scientists had mimicked #chronicpain by making a surgical nerve injury on one group of those rats; another group was a control that had a #surgery that did not cause injury. The scientists found that within three months, opioid receptor availability had gone down in several parts of the #brain in the rats with the chronic pain injury; the other group was unaffected. Other experiments explored the link between depression and chronic pain.
Other experiments explored the link between depression and chronic pain. Typically, rats will drink sugar water instead of regular water if given the option. When such animals have a symptom of depression called anhedonia, a reduced experience of pleasure, their interest in the sugar water decreases. In this work, after the injury, the rats experiencing chronic pain also had a reduced interest in the #sugarwater. These animals demonstrated a link between the availability of opioid receptors and their interest in sugar water. It’s well known that there’s a link between chronic pain and depression. The results of this study indicate that pain-induced changes in the brain’s opioid system may play a role in this association. Animals with the greatest decrease in opioid receptor availability showed the greatest increase in depression-like symptoms after experiencing chronic pain


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