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Recovery of phrenic activity and ventilation after cervical spinal hemisection in rats

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

Submitted 5 August 2005 ; accepted in final form 31 October 2005

We tested two hypotheses: 1) that the spontaneous enhancement of phrenic motor output below a C₂ spinal hemisection (C2HS) is associated with plasticity in ventrolateral spinal inputs to phrenic motoneurons; and 2) that phrenic motor recovery in anesthetized rats after C2HS correlates with increased capacity to generate inspiratory volume during hypercapnia in unanesthetized rats. At 2 and 4 wk post-C2HS, ipsilateral phrenic nerve activity was recorded in anesthetized, paralyzed, vagotomized, and ventilated rats. Electrical stimulation of the ventrolateral funiculus contralateral to C2HS was used to activate crossed spinal synaptic pathway phrenic motoneurons. Inspiratory phrenic burst amplitudes ipsilateral to C2HS were larger in the 4- vs. 2-wk groups (P < 0.05); however, no differences in spinally evoked compound phrenic action potentials could be detected. In unanesthetized rats, inspiratory volume and frequency were quantified using barometric plethysmography at inspired CO₂ fractions between 0.0 and 0.07 (inspired O₂ fraction 0.21, balance N₂) before and 2, 3, and 5 wk post-C2HS. Inspiratory volume was diminished, and frequency enhanced, at 0.0 inspired CO₂ fraction (P < 0.05) 2-wk post-C2HS; further changes were not observed in the 3- and 5-wk groups. Inspiratory frequency during hypercapnia was unaffected by C2HS. Hypercapnic inspiratory volumes were similarly attenuated at all time points post-C2HS (P < 0.05), thereby decreasing hypercapnic minute ventilation (P < 0.05). Thus increases in ipsilateral phrenic activity during 4 wk post-C2HS have little impact on the capacity to generate inspiratory volume in unanesthetized rats. Enhanced crossed phrenic activity post-C2HS may reflect plasticity associated with spinal axons not activated by our ventrolateral spinal stimulation.

plasticity; breathing

This article has been cited by other articles:

				F. J. Golder, L. Ranganathan, I. Satriotomo, M. Hoffman, M. R. Lovett-Barr, J. J. Watters, T. L. Baker-Herman, and G. S. Mitchell Spinal Adenosine A2a Receptor Activation Elicits Long-Lasting Phrenic Motor Facilitation J. Neurosci., February 27, 2008; 28(9): 2033 - 2042. [Abstract] [Full Text] [PDF]