Pain is in many ways a mysterious component of health, often having little explanation and even arising from missing limbs in amputees. To better study pain, a team from Stanford University has developed a new technique that allows them to modulate the amount of pain that specially genetically modified mice feel.
The technique relies on optogenetics, a method that introduces genes that code for light sensitive proteins into animals. In this work, the team injected a virus containing DNA of an opsin, a protein found in light-sensitive cells of the retina, into the nerves on the paws of lab mice . Weeks later, only nerves involved in pain had the opsin genes present in their DNA. Having the mice live in a cage with a transparent Plexiglas bottom, the researchers were able to shine light directly on their paws and quickly regulate how much or little pain the mice were feeling.
“The fact that we can give a mouse an injection and two weeks later shine a light on its paw to change the way it senses pain is very powerful,” [graduate student] Shrivats Iyer said.
For example, increasing or decreasing the sensation of pain in these mice could help scientists understand why pain seems to continue in people after an injury has healed. Does persistent pain change those nerves in some way? And if so, how can they be changed back to a state where, in the absence of an injury, they stop sending searing messages of pain to the brain?
Leaders at the National Institutes of Health agree the work could have important implications for treating pain. “This powerful approach shows great potential for helping the millions who suffer pain from nerve damage,” said Linda Porter, the pain policy adviser at the National Institute of Neurological Disorders and Stroke and a leader of the NIH’s Pain Consortium.
“Now, with a flick of a switch, scientists may be able to rapidly test new pain relieving medications and, one day, doctors may be able to use light to relieve pain,” she said.
The speed of the viral approach makes it very flexible, both for this pain work and for future studies. Researchers are developing newer forms of opsins with different properties, such as responding to different colors of light.