Investigation of the effects of therapeutic ultrasound or photobiomodulation and the role of spinal glial cells in osteoarthritis-induced nociception in mice

Pain is the most common symptom of osteoarthritis, and spinal glia is known to contribute to this symptom. Therapeutic ultrasound and laser therapy have been used to effectively treat osteoarthritis, with few adverse effects. Thus, this study aimed to investigate the effects of ultrasound and photobiomodulation on the symptoms and evaluate the participation of spinal glia in osteoarthritis-induced nociception in mice. Male Swiss mice were subjected to osteoarthritis induction with a 0.1-mg intra-articular injection of monosodium iodoacetate. Additionally, the mice received chronic ultrasound or photobiomodulation treatment for 21 days or a single treatment at day 14. Nociception was evaluated using von Frey filaments, and osteoarthritis symptoms were assessed by analysis of gait, joint temperature, and knee joint diameter. The role of spinal microglia and astrocytes on nociception was evaluated via an intrathecal injection of minocycline or fluorocitrate, and the spinal release of IL-1β and TNF-α was assessed by ELISA after chronic treatment with ultrasound or photobiomodulation. Our data showed that both single and chronic treatment with ultrasound or photobiomodulation attenuated the osteoarthritis-induced nociception. No differences in gait, knee joint temperature, or knee joint diameter were found. The intrathecal injection of minocycline and fluorocitrate decreased the osteoarthritis-induced nociception. There was an increase in the spinal levels of TNF-α, which was reverted by chronic ultrasound and laser treatments. These results suggest that osteoarthritis induces nociception and glial activation via spinal release of TNF-α and that the chronic treatment with ultrasound or photobiomodulation decreased nociception and TNF-α release.