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The Journal of Neuroscience, May 1, 2000, 20(9):3487-3495

Activity-Dependent Plasticity of Descending Synaptic Inputs to Spinal Motoneurons in an In Vitro Turtle Brainstem-Spinal Cord Preparation

Stephen M. Johnson and Gordon S. Mitchell

Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin 53706

An in vitro brainstem-spinal cord preparation from adult turtles was used to test the hypothesis that descending synaptic inputs to multifunctional spinal motoneurons (i.e., involved in respiration and locomotion) express activity-dependent depression or potentiation. The tissue was placed in a chamber that allowed for separate superfusion of the brainstem, spinal segments C₂-C₄, and C₅-D₁. Action potential conduction between the brainstem and spinal segments C₅-D₁ was blocked by superfusing C₂-C₄ with Na⁺-free solution. With C₅-D₁ at [K⁺] = 10 mM, electrical stimulation at C₅ every 2 min evoked potentials in intact pectoralis (expiratory, inward rotation of shoulder) and serratus (inspiratory, outward rotation of shoulder) nerves that were stable for at least 2 hr. Application of conditioning stimulation (900 pulses at 1 or 10 Hz) at C₅ decreased pectoralis evoked potential amplitudes by ~40% initially and by 20% after 90 min; serratus evoked potentials were unaltered. Conditioning stimulation (100 Hz, 900 pulses) transiently depressed pectoralis evoked potential amplitude by <20% but produced a delayed 72% increase in serratus evoked potential amplitude after ~80 min. Conditioning stimulation (10 Hz) at C₅ also reduced the amplitude of sensory afferent evoked potentials in pectoralis produced by stimulating ipsilateral dorsal roots at C₈. Thus, long-lasting changes in descending synaptic inputs to multifunctional spinal motoneurons were frequency-dependent and heterosynaptic. We hypothesize that activity-dependent plasticity may modulate descending synaptic drive to spinal motoneurons involved in both respiration and locomotion.

Key words: respiration; breathing; locomotion; LTP; LTD; motor control

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Copyright © 2000 Society for Neuroscience  0270-6474/00/2093487-09$05.00/0

This article has been cited by other articles:

				G. S. Mitchell and S. M. Johnson Plasticity in Respiratory Motor Control: Invited Review: Neuroplasticity in respiratory motor control J Appl Physiol, January 1, 2003; 94(1): 358 - 374. [Abstract] [Full Text] [PDF]

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