In people who suffer from pain disorders, painful feelings can severely worsen and spread to other regions of the body. Patients who develop chronic pain after surgery, for example, will often feel it coming from the area surrounding the initial injury and even in some parts of the body far from where it originates. New evidence suggests glia, non-neuronal cells in the brain, may be the culprits behind this effect.
Glia were once thought to simply be passive, supporting cells for neurons. But scientists now know they are involved in everything from metabolism to neurodegeneration. A growing body of evidence points to their key role in pain. In a study published today in Science, researchers at the Medical University of Vienna report that glia are involved in long-term potentiation (LTP), or the strengthening of synapses, in pain pathways in the spinal cord.
Neuroscientists Timothy Bliss and Terje Lømo first described LTP in the hippocampus, a brain area involved in memory, in the 1970s. Since then scientists have been meticulously studying the role this type of synaptic plasticity—the ability of synapses to change in strength—plays in learning and memory. More recently, researchers discovered that LTP could also amplify pain in areas where injuries or inflammation occur. "We sometimes call this a 'memory trace of pain' because the painful insult may lead to subsequent hypersensitivity to painful stimuli, and it was clear that synaptic plasticity can play a role here," says study co-author Jürgen Sandkühler, a neuroscientist also at the Medical University of Vienna. But current models of how LTP works could not explain why discomfort sometimes becomes widespread or experienced in areas a person has never felt it before, he adds.