Reactive oxygen species and inflammatory mediators enhance muscle spindles mechanosensitivity in rats

We tested the hypothesis that reactive oxygen species (ROS) and inflammatory mediators affect transduction properties of muscle spindles. In rats, muscle spindles response to high-frequency vibration (HFV) was recorded before and after (1) injection of hydrogen peroxide (H2O2) in control rats and animals pre-treated with diclofenac (anti-inflammatory substance), (2) injection of bradykinin and (3) fatigue induced by muscle stimulation (MS) in control rats and rats receiving diclofenac, superoxide dismutase (SOD) or H2O2. Muscular oxidative stress and inflammation induced by H2O2 or MS were assessed by measurements of isoprostanes and IL-6 levels. In control rats, H2O2, bradykinin and MS significantly enhanced the HFV response. Pre-treatment with SOD abolished the post-MS-enhanced HFV response whereas diclofenac lowered the peak HFV response to MS and H2O2. H2O2 injection and MS elicited significant and similar increases in isoprostanes and IL-6. We report a direct modulation of muscle spindles mechanosensitivity by ROS and inflammatory mediators.