Abstract
High cervical spinal cord injuries lead to permanent respiratory deficits. One preclinical model of respiratory insufficiency in adult rats is the C2 partial injury which causes unilateral diaphragm paralysis. This model allows the investigation of a particular population of respiratory bulbospinal axons which cross the midline at C3-C6 spinal segment, namely the crossed phrenic pathway. Transcranial magnetic stimulation (TMS) is a non-invasive technique that can be used to study supraspinal descending respiratory pathways in the rat. Interestingly, a lateral C2 injury does not affect the amplitude and latency of the largest motor-evoked potential recorded from the diaphragm (MEPdia) ipsilateral to the injury in response to a single TMS pulse, compared to a sham animal. Although the rhythmic respiratory activity on the contralateral diaphragm is preserved at 7 days post-injury, no diaphragm activity can be recorded on the injured side. However, a profound reorganization of the MEPdia evoked by TMS can be observed. The MEPdia is reduced on the non-injured rather than the injured side. This suggests an increase in ipsilateral phrenic motoneurons excitability. Moreover, correlations between MEPdia amplitude and spontaneous contralateral diaphragmatic activity were observed. The larger diaphragm activity correlated with a larger MEPdia on the injured side, and a smaller MEPdia on the non-injured side. This suggests, for the first time, the occurrence of a functional neuroplasticity process involving changes in motoneuron excitability balance between the injured and non-injured sides at a short post-lesional delay.
Highlights
High cervical spinal cord injuries often lead to respiratory insufficiencies, and ventilatory assistance is necessary in order for the patients to survive [1]
In the present study, using a preclinical animal model of respiratory insufficiency induced by a cervical spinal injury, we proposed to investigate 1) the early reorganization of the silent crossed phrenic pathway excitability by Transcranial magnetic stimulation (TMS) single pulse 1 hour and 7 days post-injury, and 2) the potential correlations of the motor-evoked potential recorded from the diaphragm (MEPdia) with the remaining spared pathways and/or the functional outcome from the contralateral intact side
This study demonstrated for the first time the use of a non-invasive transcranial magnetic stimulation technique, in the assessment of the phrenic motoneuron excitability in a preclinical model of respiratory insufficiency
Summary
High cervical spinal cord injuries often lead to respiratory insufficiencies, and ventilatory assistance is necessary in order for the patients to survive [1]. In the present study, using a preclinical animal model of respiratory insufficiency induced by a cervical spinal injury, we proposed to investigate 1) the early reorganization of the silent crossed phrenic pathway excitability by TMS single pulse 1 hour and 7 days post-injury, and 2) the potential correlations of the MEPdia with the remaining spared pathways and/or the functional outcome from the contralateral intact side. This novel non-invasive technique could be used as a diagnosis tool to evaluate the remaining functional spinal fibers spared by the initial injury and the putative functional prognosis of respiratory recovery
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