Work-related musculoskeletal disorder includes neuromusculoskeletal disorders that arise from repetitive tasks. These disorders may result from incomplete repair of tissue microtrauma induced by repeated submaximal levels of exertion. We have previously shown in a rat model that a high-repetition, negligible-force reaching and grasping task increases indicators of inflammation in both tendomuscular tissues and CNS (Barbe et al, SFN, 26(2), 2000). In this study, we examined anatomical and physiological changes in the median nerve in 19 Sprague-Dawley rats that had performed the task for 3 to 10 weeks. Median nerves within the carpal tunnel region were examined either immunocytochemically using antibodies against ED1, neutrophin 3 (NT3) and S100B, or neurophysiologically using a cuff electrode to record nerve conduction velocity (NCV). NT3 expression increased in Schwann cells (S100B-positive) within the median nerve of the reach limb by 6 weeks. All animals showed consistent, significant increases of ED1-ex...