"Our research identifies a molecular pathway by which morphine can increase pain, and suggests potential new ways to make morphine effective for more patients," said senior author Dr Yves De Koninck, Professor at Universite Laval in Quebec City.
The team included researchers from The Hospital for Sick Children (SickKids) in Toronto, the Institut universitaire en sante mentale de Quebec, the US and Italy.
The research not only identifies a target pathway to suppress morphine-induced pain but tears 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, make the pain worse," explained co-author Dr Michael Salter.
"Pain experts have thought tolerance and hypersensitivity (or hyperalgesia) are simply different reflections of the same response but we discovered that cellular and signalling processes for morphine tolerance are very different from those of morphine-induced pain," said Koninck.
"We identified specialised cells
