Optogenetic spinal stimulation promotes new axonal growth and skilled forelimb recovery in rats with sub-chronic cervical spinal cord injury.

Objective.Spinal cord injury (SCI) leads to debilitating sensorimotor deficits that greatly limit quality of life. This work aims to develop a mechanistic understanding of how to best promote functional recovery following SCI. Electrical spinal stimulation is one promising approach that is effective in both animal models and humans with SCI. Optogenetic stimulation is an alternative method of stimulating the spinal cord that allows for cell-type-specific stimulation. The present work investigates the effects of preferentially stimulating neurons within the spinal cord and not glial cells, termed 'neuron-specific' optogenetic spinal stimulation. We examined forelimb recovery, axonal growth, and vasculature after optogenetic or sham stimulation in rats with cervical SCI.Approach.Adult female rats received a moderate cervical hemicontusion followed by the injection of a neuron-specific optogenetic viral vector ipsilateral and caudal to the lesion site. Animals then began rehabilitation on the skilled forelimb reaching task. At four weeks post-injury, rats received a micro-light emitting diode (µLED) implant to optogenetically stimulate the caudal spinal cord. Stimulation began at six weeks post-injury and occurred in conjunction with activities to promote use of the forelimbs. Following six weeks of stimulation, rats were perfused, and tissue stained for GAP-43, laminin, Nissl bodies and myelin. Location of viral transduction and transduced cell types were also assessed.Main Results.Our results demonstrate that neuron-specific optogenetic spinal stimulation significantly enhances recovery of skilled forelimb reaching. We also found significantly more GAP-43 and laminin labeling in the optogenetically stimulated groups indicating stimulation promotes axonal growth and angiogenesis.Significance.These findings indicate that optogenetic stimulation is a robust neuromodulator that could enable future therapies and investigations into the role of specific cell types, pathways, and neuronal populations in supporting recovery after SCI.

Temporal and Spatial Evolution of Raised Intraspinal Pressure after Traumatic Spinal Cord Injury.

Traumatic spinal cord injury (SCI) often leads to permanent neurological impairment. Currently, the only clinically effective intervention for patients with acute SCI is surgical decompression by removal of impinging bone fragments within 24 h after injury. Recent clinical studies suggest that elevated intraparenchymal spinal pressure (ISP) limits functional recovery following SCI. Here, we report on the temporal and spatial patterns of elevated ISP following a moderate rodent contusion SCI. Compared with physiological ISP in the intact cord (2.7 ± 0.5 mm Hg), pressures increase threefold 30 min following injury (8.9 ± 1.1 mm Hg, p < 0.001) and remain elevated for up to 7 days (4.3 ± 0.8 mm Hg). Measurements of rostrocaudal ISP distribution reveal peak pressures in the injury center and in segments rostral to the injury during the acute phase(≤ 24 h). During the subacute phase(≥ 72 h), peak ISP decreases while a 7.5 mm long segment of moderately elevated ISP remains, centered on the initial contusion site. Interestingly, the contribution of the dural and pial compartments toward increased ISP changes with time after injury: Dural and pial linings contribute almost equally to increased ISP during the acute phase, whereas the dural lining is primarily responsible for elevated ISP during the subacute phase (78.9%). Our findings suggest that a rat contusion SCI model in combination with novel micro-catheters allows for direct measurement of ISP after SCI. Similarly to traumatic brain injury, raised tissue pressure is likely to have detrimental effects on spontaneous recovery following SCI.

A Cervical Hemi-Contusion Spinal Cord Injury Model for the Investigation of Novel Therapeutics Targeting Proximal and Distal Forelimb Functional Recovery.

Cervical spinal cord contusion is the most common human spinal cord injury, yet few rodent models replicate the pathophysiological and functional sequela of this injury. Here, we modified an electromechanical injury device and characterized the behavioral and histological changes occurring in response to a lateralized C4 contusion injury in rats. A key feature of the model includes a non-injurious touch phase where the spinal cord surface is dimpled with a consistent starting force. Animals were either left intact as a control, received a non-injury-producing touch on the surface of the cord ("sham"), or received a 0.6 mm or a 0.8 mm displacement injury. Rats were then tested on the forelimb asymmetry use test, CatWalk, and the Irvine, Beatties, and Bresnahan (IBB) cereal manipulation task to assess proximal and distal upper limb function for 12 weeks. Injuries of moderate (0.6 mm) and large (0.8 mm) displacement showed consistent differences in forelimb asymmetry, metrics of the CatWalk, and sub-scores of the IBB. Overall findings indicated long lasting proximal and distal upper limb deficits following 0.8 mm injury but transient proximal with prolonged distal limb deficits following 0.6 mm injury. Significant differences in loss of ipsilateral unmyelinated and myelinated white matter was detected between injury severities. Demyelination was primarily localized to the dorsolateral region of the hemicord and extended further rostral following 0.8 mm injury. These findings establish the C4 hemi-contusion injury as a consistent, graded model for testing novel treatments targeting forelimb functional recovery.