University of Central Arkansas

Abstract

      Spasticity is an abnormal reflex response to muscle stretch that commonly results in impairment following spinal cord injury (SCI) because of its interference with activities of daily living and ambulation.  The loss of supraspinal control due to SCI contributes to the development of this hyperreflexia, but the exact mechanisms have not been elucidated.  While medications can be successful in decreasing spasticity, the side effects often outweigh the benefits.  Insight into the mechanisms of spasticity and the development of more effective treatments are needed to improve the function and quality of life in individuals with SCI.

      Research into mechanisms and treatment of spasticity are necessarily dependent on methods that quantify spasticity.  Two of the commonly reported methods are (1) electrophysiological techniques such as the H-reflex, and (2) direct measures of the response to imposed muscle stretch.  This study proposes a new model for the direct measure of the electromyography (EMG) and joint torque during the imposed stretch of the calf muscles in spinal cord transected rats.  The aims of the study are to examine the effects of passive exercise on spasticity and to determine the emergence of spasticity post injury.  This data will contribute to the evidence from Dr. Skinner’s lab that shows the benefits of passive exercise based on established H-reflex measures.  Besides being a direct measure of spasticity, the new model is more similar to reflex measures in humans because anesthesia is not required, and the minimally invasive nature allows for longitudinal studies. 

      In consultation with Dr. Skinner, I have built stretching device that allows for controlled velocity and frequency of stretch to the calf muscles.  Although smaller in magnitude, stretch reflexes are present in spinal intact humans and rats.  In contrast, normal humans do not have a motor phenomenon called windup of the stretch reflex.  In human SCI, this windup or temporal summation of the EMG and torque results in larger and more prolonged responses over consecutive stretches.  This study would present the first evidence of stretch reflex windup in a SCI rat, and the windup behavior will serve as a means to quantify spasticity and make inter-group and longitudinal comparisons that are not possible by standard EMG measurement.

      Preliminary data from our lab shows the presence of windup in transected rats with no windup in uninjured controls.  The proposed study is designed to allow comparison of a transected control group and a transected group receiving daily passive exercise over an 8 week period.  Tests of spasticity will involve 2 separate protocols.  The velocity protocol will use 3 different velocities of stretch to document the emergence of stretch reflexes post injury.  The windup protocol will use 3 different frequencies to measure the amount of hyperreflexia.  Both protocols will be tested on a weekly basis.                   

      This study will provide essential information regarding the benefits of passive exercise as well as insight into possible mechanisms for the change in hyperreflexia.  Finally, there is great potential for this new model to be used in additional studies designed to examine the effects of appropriate pharmacological agents and various exercise parameters on hyperexcitable stretch reflexes.  Ultimately it is hoped that these findings can be translated into improved rehabilitation strategies in reducing hyperreflexia, and presumably spasticity in patients with SCI.

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