Diaphragm Electromyographic Activity following Unilateral Mid-Cervical Contusion Injury in Rats

Contusion type injuries to the spinal cord are characterized by tissue loss and disruption of spinal pathways. Mid-cervical spinal cord injuries impair the function of respiratory muscles and may contribute to significant respiratory complications. This study systematically assessed the impact of a 100-kDy unilateral C4 contusion injury on diaphragm muscle activity across a range of motor behaviors in rats. Chronic diaphragm EMG was recorded prior to injury, and at 1 and 7 days post injury. Histological analyses assessed the extent of perineuronal net formation, white matter sparing and phrenic motoneuron loss. At 7 days post injury, ~45% of phrenic motoneurons were lost ipsilaterally. Relative diaphragm RMS EMG activity increased bilaterally across a range of motor behaviors by 7 days post injury. The increase in diaphragm RMS EMG activity was associated with an increase in neural drive (RMS75) and was more pronounced during higher force, non-ventilatory motor behaviors. Animals in the contusion group displayed a transient decrease in respiratory rate and an increase in burst duration at 1-day post injury. By 7 days following mid-cervical contusion, there was significant perineuronal net formation and white matter loss that spanned 1mm around the injury epicenter. Taken together, these findings are consistent with increased recruitment of remaining motor units including more fatigable, high-threshold motor units during higher force non-ventilatory behaviors. Changes in diaphragm EMG activity following mid-cervical contusion injury reflect complex adaptations in neuromotor control that may increase the risk of motor unit fatigue and compromise the ability to sustain higher force diaphragm efforts.

from Physiology via xlomafota13 on Inoreader http://jn.physiology.org/cgi/content/abstract/jn.00727.2016v1?rss=1
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