Spinal Neuromodulation to Promote Physiologic and Molecular Plasticity in theInjured Spinal Cord

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Abstract There is growing interest in the use of electrical stimulation to promote the recovery of sensorimotor and autonomic function after neural injury. Previous research from our lab and others has demonstrated that stimulation of spinal lumbar segments activates central pattern generators, which, in turn, facilitates standing and walking. However, while there is extensive animal, pre-clinical, and clinical data examining the impact of lumbar stimulation, studies that apply neuromodulation to the cervical spinal cord for upper limb are very limited. Here, we propose that fundamental blind spots exist in the field of neuromodulation for upper limb, including where to stimulate anatomically, how to dose and, especially, mechanisms of action. The Horner lab has developed a clinically relevant rat model of cervical spinal cord injury and engineered a self-contained epidural stimulation device that can be deployed in freely behaving rats to stimulate sensorimotor circuitry from multiple surfaces of the spinal cord. Hence, we are well positioned to test critically important hypotheses on the role of cervical stimulation in the restoration of upper limb function. We present exciting preliminary data demonstrating that epidural stimulation of the cervical spinal cord improves forelimb function. The rationale for the proposed research is that the site of epidural stimulation provides unique access to motor circuitry. We hypothesize that ventral positioning of electrodes (VSS) will provide access to stimulate motor circuitry at the site of lesion that are inaccessible from the more common dorsal approach (DSS). Further, we propose that VSS will produce novel mechanisms of function plasticity that can amplify recovery when combined with DSS. To test this hypothesis, we propose the following aims: Aim 1: Determine acute molecular and physiological mechanisms of VSS when applied to subacute cervical spinal cord injury. Aim 2: Establish the functional impact of site of stimulation and rehabilitative training on recovery from early chronic cervical spinal cord injury. Aim 3: Establish the synergistic effects of combined VSS and DSS after cervical spinal cord injury. These studies will explore an exciting new approach to promote neural recovery of the upper limb, an area of research that has had limited investigation, but remains a primary concern for the patient. Our approach will rigorously establish the physiological and functional effects of the site of stimulation on the molecular and physiological mechanisms of upper limb plasticity.