Optimizing Photoneuromodulation Techniques to Evaluate the Role of Green Light-Emitting Diodes in Pain Management

Our research focuses on managing pain without medication by using photoneuromodulation with green light emitting diode, an approach that we called GLED. We aim to determine how GLED modulates pain pathways, but also identify optimal exposure parameters for both preclinical and clinical studies. The field of photoneuromodulation is still in its infancy and we're just beginning to scratch the surface of its potential. This approach is opening many new doors, particularly in understanding how it affects synaptic plasticity and neuroinflammation.

Challenges include optimizing light intensity and exposure duration in different mode pain models and between animals and humans, and ensuring the consistency in pain assessment across both studies. Additionally, translating the preclinical studies to human application require further acceleration. We established that GLED therapy using a specific wavelength of 525 nanometer effectively modulates pain pathways. This non-invasive, non-pharmacological approach has demonstrated significant success in alleviating both acute and chronic pain and conditions such as migraine, fibromyalgia and post-surgical pain.

This protocol addresses a gap in inconsistent GLED exposure methodologies across studies by standardizing parameters such as intensity, duration and setup. The protocol ensures reproducibility and consistency in both preclinical and clinical studies.

[Narrator] To begin, obtain visible spectrum LED flex strips for the procedure. Using a lux meter, measure and optimize the light intensity and cover the LEDs with black tape as needed to achieve the desired intensity. Then secure the LED strips to the upper edges of wire shelves in a dark room to ensure each shelf has a dedicated light exposure source. Attach timers to the LED strips to expose the cages for eight hours per day from 6:00 AM to 2:00 PM. Use a lux meter to finalize light intensity optimization inside the cages after covering or uncovering some of the LEDs. Next, acclimate the rat in a clear plexiglass box on a wire mesh for one hour prior to testing in the same room with the experimenter present. Measure the paw withdrawal thresholds using the Dixon up-and-down method with Von Frey filaments on the left hind paw. Now place the rat in a clear plexiglass box on the Hargreaves apparatus for one hour and measure the baseline thermal sensitivity using the Hargreaves test. To assess preoperative behavioral thresholds, position the infrared laser under the center of the animal's left hind paw. Start the heat stimulus and record the time it takes for the animal to withdraw its paw in response to the heat. After acquiring baseline sensory behaviors, house the animal in static cages for light exposure with continuous access to food and water for four days before surgery. After the light exposure concludes at 2:00 PM On day four, perform an incision surgery on the left hind paw following the Brennan model to induce postoperative pain. On day five, conduct Von Frey and Hargreaves tests as demonstrated. Prepare the exposure room ensuring it is completely free of any external light sources to eliminate potential interference. Position the LED lights at a distance of three to six feet from the subject's chair. Then use a lux meter to ensure the light intensity range is between 90 and 100 lux in the primary area where the patient is seated. Instruct the patient to rate their pain on a scale from zero to 10. For single application measurements, apply the Von Frey filament three times at three different points with a five second interval. To measure temporal summation, apply the filament once per second for a total of 10 times. Then ask the subject to rate the pain of the final application. After familiarization, let the patient take a three minute break. Then apply the filament three times at three different points on the dominant trapezius muscle with a five second interval between applications. Measure the temporal summation effect after 10 applications on the dominant trapezius and record the subject's response. For conditioned pain modulation evaluation, prepare a 12 degree Celsius cold water bath. Open the MEDOC software for CPM evaluation. Select the Algomed option on the home screen, and choose the algometer device to activate it. After choosing the correct patient, select the appropriate test program. Select the site for device application. For familiarization, choose the non-dominant trapezius muscle from the body diagram. Inform the patient that the device measures the amount of pressure applied and will be used to apply pressure to the non-dominant side of the trapezius muscle. Instruct the patient to say stop as soon as they begin to feel any pain. Click start on the system to initiate the test, which will impose a five second wait before applying pressure, apply the algometer to the trapezius muscle increasing force at a rate of 30 kilopascals per second. Record the patient's response on the record sheet. Check the water temperature in an ice water bath using a thermometer to ensure it is around 12 degrees Celsius before starting the timer for 10 seconds. Instruct the participant to immerse their dominant hand in the water up to the wrist, ensuring the hand is relaxed and the fingers are spread apart. At the end of 10 seconds, ask the participant to rate their pain on a scale from zero to 10 when the operator says now. After a three minute break, request permission to expose the dominant trapezius muscle for the conditioned pain modulation or CPM assessment. Click start on the software to begin and instruct the patient to say stop as they begin to feel any pain. Now apply the algometer on the trapezius muscle, increasing the force at a rate of 30 kilopascals per second. Record the patient's response on the record sheet. Five minutes later, instruct the patient to immerse their nondominant hand up to the wrist in the ice water bath. Apply the algometer to the trapezius muscle, increasing the force at a rate of 30 kilopascals per second and record the response. After determining the baseline, expose the patient to the assigned LED light for 1.5 hours. Following the light exposure therapy, repeat all the measurements completed at the baseline. Increasing intensities of green LED significantly elevated paw withdrawal latencies in rats over seven days with the strongest antinociceptive effect observed at 200 lux. Green LED exposure at 100 lux effectively reversed mechanical hypersensitivity in a paw surgery induced rat pain model. Significantly increasing paw withdrawal thresholds over two days. Daily green LED exposure significantly reversed thermal hypersensitivity shown by increased paw withdrawal latencies post-incisional surgery in rats. Mechanical sensitivity was enhanced by temporal summation and reduced by conditioned pain modulation.