October Shining a Light on Chronic Pain

A recent study from researchers at CÚRAM, the Science Foundation Ireland Research Centre for Medical Devices at NUI Galway, explores the use of optogenetics as a method to relieve chronic pain. Optogenetics uses genetically-encoded proteins that change position and shape in the presence of light to turn brain cells on or off.  

Pain is comprised of both sensory (physical intensity) and affective (emotional distress) components. A part of the brain involved in the emotional component of pain is called the anterior cingulate cortex (ACC).

Dr Sarah Jarrin, CÚRAM, NUI Galway and first author of the paper, said: “There is significant overlap in the neural circuitry of pain and anxiety in our brains. Sensory pain is our body’s natural alarm system, it is an important mechanism that alerts us to injury and danger. So rather than turning off that alarm system, we are targeting the distress component of pain, a promising target for chronic pain relief that is not addressed by current treatments.

“The technique of optogenetics is opening up lots of possibilities for further neuroscience research. With the use of light-activated proteins called opsins, optogenetics allows us to switch on or off a selective population of neurons that control this affective component of pain.”

The study, funded by Science Foundation Ireland (SFI), focused on the two components of pain (physical and emotional), the distinct roles they play in the pain experience, and how they can often influence one another.

Chronic pain and anxiety frequently go hand in hand. People with chronic pain are also more likely to have anxiety and depression than the general population. The research looked specifically at the role of glutamatergic neurons of the ACC (glutamatergic neurons release the chemical transmitter glutamate, responsible for signalling between nerve cells) and changes in a protein marker of neuronal activity, known as c-Fos, in the ACC.

The study was able to show that when the glutamatergic neurons in the ACC were silenced, it is possible to abolish the aversion to pain without affecting the sensory component of pain. The study also showed that optogenetic activation of glutamatergic neurons of the ACC has a differential effect in males and females in terms of pain response.

Dr Jarrin added: “The inclusion of both sexes in pain studies is critical, because of differences in pain that have been observed between the sexes. Little is known about differences in the regulation of the physical and emotional components of pain in the male and female brain. Studies have found differences in the functional connectivity between the ACC and other brain regions of important regulating pain in males and females, which may account for differences in the effect of optogenetic treatment."

Being able to target the emotional component of pain specifically could be therapeutically beneficial for patients with chronic pain, however further research to better understand the neural circuitry is required to develop these improved treatments.

Professor David Finn, Co-Director of NUI Galway’s Centre for Pain Research and principal investigator on the published study, said: “We are excited to publish these interesting data which advance our understanding of how the brain regulates pain, and how this may differ between males and females.”

The study was carried out as part of Dr Sarah Jarrin’s PhD project, jointly supervised by Dr David Finn, Dr Michelle Roche and Dr Abhay Pandit at NUI Galway.

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