Upper extremity skeletal muscle adaptations following high cervical spinal cord injury (SCI) in adult rats

Abstract

Most SCI's occur in the cervical region, but the response of upper extremity skeletal muscle to chronic cervical SCI has not been carefully described. In ongoing experiments, we are quantifying the effects of unilateral cervical SCI on upper extremity skeletal muscle in adult male Sprague-Dawley rats. Triceps brachii muscle tissue was harvested following lateral C2 spinal hemisection and compared with data from uninjured rats. Standard immunohistochemical techniques were used to quantify fiber size and fiber type composition. In uninjured animals, fiber size was consistent between limbs and the deep triceps was comprised of roughly 25% type I fibers, 35% type IIa fibers, and the remainder, type IIx/IIb fibers. At 1 week post-SCI, considerable remodeling was observed ipsilaterally, as demonstrated by a marked reduction in fiber size. Additionally, a shift in fiber type composition was observed, with type I fibers comprising less than 10% and type IIa fibers comprising only 15% of the deep triceps. Fiber type composition of contralateral triceps was similar to uninjured muscle. At 8 weeks post-SCI, almost no type I fibers were present ipsilaterally, and a sizeable increase in the proportion of fast fiber types (IIa/IIb/IIx) was evident. These preliminary data indicate rapid and extensive remodeling occurring in upper extremity muscles following cervical SCI. Research Support: NIH T32HD043730 & 1R01HD052682-01A1