Pain is perceived by electrical impulses in neurons.
"The constant perception of pain severely influences the quality of life of the patients and represents an extraordinary emotional burden," says lead author Thomas Nevian from the Department of Physiology at the University of Bern.
Nevian explains that despite chronic pain affecting more than 1 million people in Switzerland alone (about 100 million Americans are affected by the condition), proper treatment strategies are missing in many cases.
"Thus," he says, "understanding the development of chronic pain is of outmost importance for neuroscience research."
Neurons in the gyrus cinguli create a 'pain memory'
Nevian and colleagues' discovery is the identification of a cellular mechanism in a brain region called gyrus cinguli, which is typically associated with the emotional aspects of pain. In a mouse model, the researchers found that neurons in this region are modified by chronic pain, establishing a form of "pain memory."
"The neurons are constantly activated by a noxious stimulus," explains Nevian, "thus building a memory trace for pain that becomes irreversible. Our idea was to understand this mechanism better to derive potential new treatment strategies."
Because pain is perceived by electrical impulses in neurons, the researchers looked for electrical fluctuations among neurons in the limbic system. They found such changes - "more excitable" neurons - in the gyrus cinguli.
They believe that the neurons were more excitable here due to a down-regulation of an ion channel, which instead of regulating electrical properties of cells, leads to an increased number of nerve impulses in these cells. The increase in nerve impulses is therefore perceived by the brain as pain.
Next, the researchers attempted to restore the function of the ion channel. They succeeded in doing this by activating a receptor sensitive to serotonin. Nevian explains the role serotonin plays in reactivating the ion channel:
"It has been known for some time that serotonin can modulate pain perception and the function of some drugs is based on this. Nevertheless, what is new in our study now is that we were able to identify a specific subtype of serotonin receptor that reduced the perception of pain more efficiently. This is an important result, which might help to treat chronic pain more efficiently in the future."
An interesting additional finding of this research is that the results suggest a mechanism to explain how tricyclic antidepressants work. Previously, it has been assumed that tricyclics work by acting on the spinal cord, but the Bern study shows that they also work directly on pain perception in the brain.
However, Nevian says that even though he believes an important step has been made in this research, it will be some time before novel drugs are designed based on these results.
Recently, Medical News Today looked at a potential new treatment for chronic pain found in a somewhat unexpected source - spider venom.