Quantitative Biosciences Dissertation Proposal
Elma Kajtaz
School of Biological Sciences
Thesis Advisor: Dr. T. Richard Nichols
Open to the community
QUANTITATIVE ANALYSIS OF AUTOGENIC AND INTERMUSCULAR PATHWAYS IN CATS WITH SPINAL CORD INJURY
Friday, March 30, 2018
8:00am
Main Auditorium, Applied Physiology Building
555 14th Street NW, Room 1253
Committee Members:
Dr. Dena Howland
School of Neurological Surgery, Anatomy Sciences & Neurobiology, Bioengineering
University of Louisville
Dr. Timothy Cope
School of Biological Sciences
Georgia Institute of Technology
Dr. Simon Sponberg
School of Physics
Georgia Institute of Technology
Dr. Boris Prilutsky
School of Biological Sciences
Georgia Institute of Technology
Abstract:
It is well established that sensory feedback regulates the mechanical properties of limbs, particularly when the limbs interact with the environment. This is accomplished through integration of sensory information from various systems, but mainly length-dependent feedback from muscle spindle receptors and force-dependent feedback from Golgi tendon organs. Briefly, length-dependent feedback from muscle spindle receptors increases joint stiffness, and intermuscular, inhibitory force-dependent feedback from Golgi tendon organs reduces limb stiffness, while excitatory force-feedback enhances joint coupling during locomotion. Inhibitory force feedback is a widely-distributed system which links cross-joint extensor muscles. It has shown remarkable task-dependent modulation by descending pathways and previous research has shown that the magnitude of force feedback appears to be an important control variable in the modulation of limb stiffness during locomotion. Thus, inability to modulate this reflex pathway properly after spinal cord injury (SCI), could be a critical barrier limiting recovery during rehabilitation. Here, we report preliminary evidence suggesting that disruption of supraspinal tracts in the spinal cord alters the magnitude and intermuscular distribution (bias) of force feedback drastically and chronically. In cats with a lateral T9 hemisection, the magnitude of force feedback from both distal and proximal muscles onto ankle extensor muscles – notably feedback from flexor hallucis longus and vasus muscles onto gastrocnemius – is greatly amplified compared to control animals. While decerebrate, control animals exhibit various profiles of force feedback distribution, the convergence of inhibition onto ankle extensors in cats with spinal cord damage seems to be a consistent pattern across SCI cats studied. To thoroughly evaluate changes following SCI of both length-dependent and force-dependent pathways we will investigate changes in autogenic feedback (Aim 1) and intermuscular feedback (Aim 2). Furthermore, we will reconstruct hindlimb kinematics from mechanographic data (Aim 3) and identify the location of the descending tract responsible for regulation of force-dependent feedback (Aim 4). The analysis and further experiments to this end are underway. In this proposal, the preliminary results for Aim 1 and 2 will be presented.
