Development of an <i>in vivo</i> electrophysiological assessment system for evaluating the analgesic effects of photobiomodulation

Photobiomodulation (PBM) has gained significant attention as a non–invasive and effective treatment for pain. However, the precise mechanisms and quantitative assessment of PBM’s effects remain unclear. This study aimed to develop an in vivo electrophysiological evaluation system to quantitatively measure the effects of PBM, using the firing frequency of neurons in the spinal dorsal horn as an indicator. An 808 nm semiconductor laser was used to irradiate the sciatic nerve in rats, and the neuronal responses evoked by the von Frey filaments were measured. Our findings revealed that PBM significantly suppressed the firing frequency evoked by a 15.0 g von Frey filament, with effects persisting up to 180 min post–irradiation, whereas no changes were observed in the sham group. Additionally, PBM reduced neuronal responses to varying von Frey filament intensities, suggesting a selective effect on noxious stimuli. This evaluation system offers a robust and quantitative method for assessing the effects of PBM, and provides valuable insights into its mechanisms. This tool has the potential to enhance clinical outcomes and improve the chronic pain by providing a precise and reliable means of assessing the efficacy of PBM.