FLICKR, WOODLEYWONDERWORKSWhen the body suffers an acute injury, it releases natural opioid compounds that have an immediate analgesic effect, making painful accidents much more tolerable. But that pain-reducing system may be a double-edged sword, according to a mouse study published today (September 19) in Science: the process appears to switch a natural opioid receptor into a chronically “on” position; flipping it back “off” leads to a resurgence of pain in the animals, even months after the initial injury. Moreover, the pain behaviors that resurfaced when the receptor was turned off looked strikingly like those associated with opioid withdrawal.
“You have the same system, the same structure, involved in both the effect of analgesia—in reducing pain sensation—and in opioid dependence and chronic pain,” said neurobiologist Flaminia Pavone of the Cell Biology and Neurobiology Institute in Italy, who was not involved in the work. “[It’s] a paradoxical effect that can lead to more sensitivity to pain.”
Chronic pain can arise following acute injuries. Chronic back pain, for example, is often preceded by lower back injuries. When and why acute pain is translated into chronic pain, however, is largely unknown. Sensory neurobiologist Bradley Taylor from the University of Kentucky Medical Center and his colleagues wondered whether the answer might lie in the body’s mechanisms for controlling pain in the first place. “We know that the body ...
