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Author Notes:

Address for reprint requests and other correspondence: S. Hochman, Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322 (E-mail: shochm2@emory.edu) or Y. H. Chang, School of Applied Physiology, Georgia Institute of Technology, Atlanta, GA 30332 (E-mail: yh.chang@ap.gatech.edu)

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Research Funding:

This work was funded by National Institutes of Health Grants NS-40893 and NS-045248 to S. Hochman and AR-054760 to Y.-H. Chang, National Science Foundation (NSF) Integrative Graduate Education and Research Traineeship Grant DGE-0333411, and NSF Graduate Research Fellowship Program grant to H. B. Hayes.

An In Vitro Spinal Cord-Hindlimb Preparation for Studying Behaviorally Relevant Rat Locomotor Function

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Journal Title:

Journal of Neurophysiology

Volume:

Volume 101, Number 2

Publisher:

, Pages 1114-1122

Type of Work:

Article | Post-print: After Peer Review

Abstract:

Although the spinal cord contains the pattern-generating circuitry for producing locomotion, sensory feedback reinforces and refines the spatiotemporal features of motor output to match environmental demands. In vitro preparations, such as the isolated rodent spinal cord, offer many advantages for investigating locomotor circuitry, but they lack the natural afferent feedback provided by ongoing locomotor movements. We developed a novel preparation consisting of an isolated in vitro neonatal rat spinal cord oriented dorsal-up with intact hindlimbs free to step on a custom-built treadmill. This preparation combines the neural accessibility of in vitro preparations with the modulatory influence of sensory feedback from physiological hindlimb movement. Locomotion induced by N-methyl d-aspartate and serotonin showed kinematics similar to that of normal adult rat locomotion. Changing orientation and ground interaction (dorsal-up locomotion vs ventral-up air-stepping) resulted in significant kinematic and electromyographic changes that were comparable to those reported under similar mechanical conditions in vivo. We then used two mechanosensory perturbations to demonstrate the influence of sensory feedback on in vitro motor output patterns. First, swing assistive forces induced more regular, robust muscle activation patterns. Second, altering treadmill speed induced corresponding changes in stride frequency, confirming that changes in sensory feedback can alter stride timing in vitro. In summary, intact hindlimbs in vitro can generate behaviorally appropriate locomotor kinematics and responses to sensory perturbations. Future studies combining the neural and chemical accessibility of the in vitro spinal cord with the influence of behaviorally appropriate hindlimb movements will provide further insight into the operation of spinal motor pattern-generating circuits.

Copyright information:

© 2009, American Physiological Society

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