New research indicates that long-term use of opioids can increase the severity of the treated pain, a condition known as hyperalgesia. Scientists with the University of Colorado Boulder led the investigation by testing morphine on lab rats. Lead author of the study and neuroscientist, Peter Grace, said the association between opioid and pre-existing pain hasn’t been adequately studied and are looking for the connection between hyperalgesia and its effect on the immune system.
Lead author of the study and neuroscientist, Peter Grace, said the association between opioid and pre-existing pain hasn’t been adequately studied and are looking for the connection between hyperalgesia and its effect on the immune system.
Researchers used rats to stage the same effects of chronic nerve pain in humans usually as a result from stroke, traumatic nerve injury, or nerve damage caused by diabetes. Scientists sliced into the rats’ thighs and tied off a major nerve to cause painful constriction. The tiny used dissolved after six weeks. Later, scientists injected morphine into them for five days.
Over three months scientists recorded the rats’ reactions to pain by prodding their hind paws with nylon threads with various thicknesses. Researchers found the rats were more sensitive to the finer thread. Following six weeks, the lab rats didn’t receive morphine injections and were poked but reacted the same way as pokes to uninjured rats.
But when it came to morphine-treated lab rats, they reacted more severely to pokes with a finer hair. More than 12 weeks passed before these rats returned to the same level of sensitivity as the other rats. Evidence suggests opioids can paradoxically cause an elevation in chronic pain even after only a few days of morphine treatment.
Researchers noted this happened because the morphine increased the release of pain receptors from particular immune cells in the spinal cord; distinctly, a protein known as interleukin-1beta (IL-1b), which stimulates the responsiveness of nerve cells in the brain and spinal cord leading to an extended release of pain.
Thus, Grace said the results suggest opioid prescriptions bumped up in humans may even antagonize chronic pain.”We found the treatment was contributing to the problem,” said Grace, who is also an associate professor at CU-Boulder. The full report was published in Tech Times.