Substance P, NK1, and NMDA receptor 1 increase in spinal cord dorsal horns in a rat model of repetitive motion injury.
Elliott MB; Barr AE; Barbe MF; Fedorcyzk J; Amin M
Neuroscience 2006, October 14-18, 2006, Atlanta, Georgia. Washington, DC: Society for Neuroscience, 2006 Oct; :738.21/P14
Recent studies in patients have identified the presence of neurochemicals, such as Substance P, in forelimb tendons in association with chronic tennis elbow. Our lab has developed a rat model of upper extremity repetitive motion injury. Recently, we found that performance of this task resulted in increased levels of Substance P and NMDAr1 in flexor forelimb tendons. In the present study, we investigated neurochemical changes in spinal cords following 10 weeks of either a high repetition high force (HRHF), a high repetition low force (HRLF), or a low repetition low force (LRLF) task. A total of 46 Sprague-Dawley rats were used: 12 performed the HRLF task, 12 performed the HRHF task, 12 performed the LRLF tasks, and 10 were controls. For the HRLF and LRLF tasks, rats reached and retrieved a 45 mg food pellet at a target reach rate of 4 reaches/min (HRLF), or 2 reaches/min (LRLF). For the HRHF task, rats grasped and pulled on a handle at a target force level of 60% maximum grip force, and at a target reach rate of 4 reaches/min. This task was performed in 4, 0.5 hour sessions separated by 1.5 hours for 3 days/week for periods of up to 10 weeks. For histological analysis, animals were euthanized using Nembutol (120 mg/kg body weight) and perfused with 4% paraformaldehyde in 0.1M phosphate buffer (pH= 7.4). Spinal cords were collected, frozen sectioned and examined immunohistochemically for Substance P, Neurokinin 1, and NMDAr1. In the HRLF and HRHF rats, Substance P, NK1 and NMDAr1 were significantly increased in laminae I and II of cervical segments of the spinal cord in dorsal horns ipsilateral to the reach limb compared to LRLF and control rats. This increase in a spinal cord neuropeptide and its receptors correlate with findings of peripheral tissue inflammation in the forearm, as well as increases in peripheral tissue Substance P levels. This increased neurochemical response centrally may be linked to persistent chronic pain associated with repetitive motion injuries.
Animals; Laboratory-animals; Models; Repetitive-work; Musculoskeletal-system; Musculoskeletal-system-disorders; Age-groups; Force; Tissue-culture; Behavior; Bone-structure; Injuries; Cumulative-trauma; Cumulative-trauma-disorders
Neuroscience 2006, October 14-18, 2006, Atlanta, Georgia
Temple University, Philadelphia, Pennsylvania