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For individuals with agonizing pain, it is a cruel blow when the gold-standard medication actually causes more pain. Adults and children whose pain gets worse when treated with morphine may be closer to a solution, based on research published in the January 6 on-line edition of Nature Neuroscience.
“Our research identifies a molecular pathway by which morphine can increase pain, and suggests potential new ways to make morphine effective for more patients,” says senior author Dr. Yves De Koninck, Professor at Université Laval in Quebec City. The team included researchers from The Hospital for Sick Children (SickKids) in Toronto, the Institut universitaire en santé mentale de Québec, the US and Italy. New pathway in pain management The research not only identifies a target pathway to suppress morphine-induced pain but teases apart the pain hypersensitivity caused by morphine from tolerance to morphine, two phenomena previously considered to be caused by the same mechanisms. “When morphine doesn’t reduce pain adequately the tendency is to increase the dosage. If a higher dosage produces pain relief, this is the classic picture of morphine tolerance, which is very well known. But sometimes increasing the morphine can, paradoxically, makes the pain worse,” explains co-author Dr. Michael Salter. Dr. Salter is Senior Scientist and Head of Neurosciences & Mental Health at SickKids, Professor of Physiology at University of Toronto, and Canada Research Chair in Neuroplasticity and Pain. “Pain experts have thought tolerance and hypersensitivity (or hyperalgesia) are simply different reflections of the same response,” says Dr. De Koninck, “but we discovered that cellular and signalling processes for morphine tolerance are very different from those of morphine-induced pain.” Dr. Salter adds, “We identified specialized cells – known as microglia – in the spinal cord as the culprit behind morphine-induced pain hypersensitivity. When morphine acts on certain receptors in microglia, it triggers the cascade of events that ultimately increase, rather than decrease, activity of the pain-transmitting nerve cells.”
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