Nasal OEC transplantation promotes respiratory recovery in a subchronic rat model of cervical spinal cord contusion.

Engraftment of nasal olfactory ensheathing cells (OEC) is considered as a promising therapeutic strategy for spinal cord repair and one clinical trial has already been initiated. However, while the vast majority of fundamental studies were focused on the recovery of locomotor function, the efficiency of this cellular tool for repairing respiratory motor dysfunction, which affects more than half of paraplegic/tetraplegic patients, remains unknown. Using a rat model that mimics the mechanisms encountered after a cervical contusion that induces a persistent hemi-diaphragmatic paralysis, we assessed the therapeutic efficiency of a delayed transplantation (2 weeks post-contusion) of nasal OECs within the injured spinal cord. Functional recovery was quantified with respiratory behavior tests, diaphragmatic electromyography and neuro-electrophysiological recording of the phrenic motoneurons while axogenesis was evaluated using immunohistochemistry. We show that 3 months post-transplantation, nasal OECs improve i) breathing movements, ii) activities of the ipsilateral diaphragm and corresponding phrenic nerve, and iii) axonal sprouting in the injury site. We also demonstrate that this functional partial recovery is mediated by the restoration of ipsilateral supraspinal command. Our study brings further evidence that olfactory ensheathing cells could have clinical application especially in tetraplegic patients with impaired breathing movements. This article is part of a Special Issue entitled: Understanding olfactory ensheathing glia and their prospect for nervous system repair.

Diaphragm recovery by laryngeal innervation after bilateral phrenicotomy or complete C2 spinal section in rats.

This study aimed to highlight the functional aspects of diaphragm reinnervation by laryngeal motoneurons after bilateral phrenicotomy or complete cervical transection. The left recurrent laryngeal nerve was connected to the left phrenic nerve in 14 rats. Five months later, all bridged rats presented a substantial ipsilateral diaphragm recovery (74.2 +/- 10% of contralateral activity) whereas the diaphragm remained paralysed in non-bridged rats (n = 5/5). After additional right phrenicotomy, functional breathing persisted in bridged rats whereas all non-bridged died. After complete C2 spinal transection, diaphragm respiratory discharges persisted in bridged rats. The reinnnervation by laryngeal motoneurons was confirmed by retrograde labeling, stimulus-elicited diaphragm response by vagal stimulation and diaphragm inactivation after vagotomy. In conclusion, the recurrent-phrenic nerve anastomosis induces a reliable functional diaphragm outcome even after contralateral diaphragm denervation or complete high cervical spinal cord injury, and could be considered as a clinical repair strategy for re-establishing diaphragm autonomy following spinal cord trauma.

A new model of upper cervical spinal contusion inducing a persistent unilateral diaphragmatic deficit in the adult rat.

Research on spinal cord trauma requires models reflecting the contusion mechanisms encountered in clinical situation. The aim of this study was to develop in the adult rat a reproducible model of upper cervical spinal cord contusion inducing persistent unilateral diaphragm deficit. After dura and pia matter removal, weight drop and compression were targeted at the ventro-lateral funiculi which contain the bulbospinal descending respiratory pathways that command the phrenic motoneurons innervating the diaphragm. At 7 days post-injury, the left diaphragm activity recorded in contused rats (27.4 +/- 5.1% of the contralateral activity) was significantly lower than in the sham group (97.6 +/- 1.2%). This respiratory deficit still persisted 1 month later. Histology showed a reproducible left C2-lateralized lesion that involved both white and gray matter including the ventro-lateral funiculi. This C2 contusion model provides a basis for testing both regenerative and neuroprotective strategies aimed at improving functional respiratory recovery after spinal cord trauma.

Phrenic rehabilitation and diaphragm recovery after cervical injury and transplantation of olfactory ensheathing cells.

Functional respiratory recovery was evaluated by recording diaphragm and phrenic nerve activity several months after cervical cord hemisection followed by olfactory ensheathing cell (OEC) transplantation. The intact side was taken as a control in each rat. Sham-transplanted rats did not recover respiratory activity from the ipsilateral lesioned side. By contrast, ipsilateral phrenic and diaphragmatic activities recovered in transplanted rats amounted to 80.7% and 73% of their controls, respectively. After contralateral acute C1 section eliminating any contralateral influence from crossed compensatory pathways, the ipsilateral phrenic activity remained at 57.5% of the control, indicating that the phrenic recovery originated from the ipsilateral side. Supralesional stimulation in these rats elicited sublesional ipsilateral postsynaptic phrenic responses showing that transplantation helped ipsilateral fibers to again transmit nervous messages to the phrenic target, leading to substantial functional recovery. The origin of mechanisms involved in respiratory recovery (regeneration, resurrection, sprouting, sparing, demasking of latent pathways) is discussed.