Cervical excitatory neurons sustain breathing after spinal cord injury
Alex Laliberte, Michael Fehlings, Kajana Satkunendrarajah, Spyridon Karadimas, Gaspard Montandon
Introduction: Respiratory insufficiency is the leading cause of morbidity and mortality after traumatic cervical spinal cord injury (SCI). In contrast to acute and traumatic SCI, non-traumatic spinal cord injury (ntSCI) results in subclinical and mild respiratory dysfunction.
Objective: This study seeks to understand the mechanism of this respiratory plasticity in ntSCI and investigates a novel therapeutic strategy to restore breathing immediately after SCI.
Methods: ntSCI was modeled in the form cervical myelopathy. Phrenic motoneurons (PMNs) and cervical interneurons were retrogradely traced via cholera toxin b and pseudorabies technology, respectively. Excitatory input onto PMNs were examined using vesicular glutamate transporter 2 (Vglut2)+boutons on PMNs. To confirm the role of cervical glutamatergic neurons in promoting respiratory plasticity and breathing in ntSCI and chronic SCI, we injected AAV-FLEX-PSAML141F–GlyR-IRES-eGFPin the ventromedial area of C3-5 spinal levels of Vglut2::cre mice two week prior to the induction of ntSCI or SCI. Finally, we examined the efficacy of pharmacogentic stimulation of these cervical glutamatergic neurons in restoring breathing immediately after traumatic SCI.
Results: Combination of pharmacogenetics and respiratory physiology assays showed that midcervical excitatory interneurons are essential for the maintenance of breathing in ntSCI and critical for promoting respiratory recovery after traumatic SCI. Importantly, stimulation of cervical excitatory interneurons following traumatic SCI was sufficient to rescue breathing in mice at the acute stage, the most critical period for SCI patients.
Conclusions: This is the very first study demonstrating a strategy to restore breathing immediately after cervical SCI. In future, viral vectors can be used to target this subpopulation in humans with SCI.