Researchers discover new pathway to reduce paradoxical pain



Relief may be close for adults and children whose pain gets worse when treated with morphine, thanks to a Canada-based research team.

"Our research identifies a molecular pathway by which morphine can increase pain, and suggests potential new ways to make morphine effective for more patients," Dr. Yves De Koninck, a professor at Université Laval in Quebec City, and the paper's senior author said in a statement Sunday.

The team included researchers from The Hospital for Sick Children in Toronto, the Institut universitaire en santé mentale de Québec, the U.S. and Italy.

Their paper was published in the January 6 on-line edition of Nature Neuroscience.

"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," the paper's co-author, Dr.

Michael Salter, said. Salter is a scientist and head of Neurosciences & Mental Health at SickKids and a professor of Physiology at the University of Toronto.

"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."

Salter says the discovery could have a major impact on those suffering from various types of intractable pain, such as those associated with cancer or nerve damage, who have stopped morphine or other medications because of pain hypersensitivity.

The Canadian Pain Society estimates that chronic pain affects at least one in five Canadians and costs Canada $55-60 billion per year, including health care expenses and lost productivity.

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