Researchers at the Montreal Neurological Institute and Hospital of McGill University and the McGill University Health Centre (Montreal, QC, Canada) have shown the potential of optogenetics as a noninvasive, highly focused method of pain management. By genetically modifying mice with a yellow light-sensitive trait in the Nav 1.8+ nociceptors known to be responsible for pain transmission, they express proteins called opsins that react to light.
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When Nav 1.8+ nociceptors are exposed to yellow light, the opsins move ions across the membrane, reducing the level of bioelectric activity of the cells--a process known as optogenetics. This effectively shuts off the neurons, decreasing the mouse's sensitivity to touch and heat.
"The opsins we added to these neurons were initially isolated from archaebacteria and sense yellow light," explains Professor Philippe Séguéla, a researcher at the Montreal Neurological Institute and Hospital and the article's senior author. "When we transfer these to neurons, we can control their responses simply by illuminating the skin with innocuous yellow light."
The activity of pain-signaling neurons was reduced in a localized part of the mouse's body, the hind paw, and the duration of the effect could easily be controlled by the amount of time the light was applied. The precision of this technique underlines potential advantages for use in humans.
Light therapy based on optogenetics would have the advantage of providing "on-demand" analgesia (pain relief) to patients who could control their pain by shining light on the sensitive part of the body. Opiates are the most commonly used treatment for chronic pain, but they are often used systemically and not directed to the specific region of the body affected by the pain. The duration of the opiate effects can be estimated, but without the same precision as a beam of light.
Further advances in neuroscience are necessary to apply this method of pain relief to humans. Séguéla says one possible way to make human neurons photosensitive would be through the use of a harmless virus that could temporarily deliver opsins to certain neurons without causing side effects.
Full details of the work appear in the journal eNeuro; for more information, please visit http://dx.doi.org/10.1523/eneuro.0140-15.2016.