Restoration of hand and arm function is the highest treatment priority for people with cervical spinal cord injury. The goal of this research is to develop and test a novel method to improve recovery of hand and arm function after spinal cord injury. We propose to use optogenetic stimulation of the cervical spinal cord to both improve function and to uncover the mechanisms by which spinal cord stimulation leads to recovery. Our preliminary data demonstrate both a rapid and near complete recovery of forelimb function when animals receive optogenetic spinal cord stimulation following a clinically-realistic cervical spinal cord contusion injury. Optogenetic light stimulation may provide benefits by both directly activating neural circuits and also by increase blood flow to the injured spinal cord. Here we propose to compare the functional recovery resulting from optogenetic and electrical spinal cord stimulation, as well as the combination of electrical and light stimulation delivered to nave animals that do not express optogenetic proteins. Our experiments are enabled by a novel multifunctional electrode that permits both optical and electrical stimulation to be delivered to the surface of the spinal cord in rodents. These flexible polymer electrodes will be refined in Aim 1 to deliver chronic optogenetic and epidural electrical stimulation to the rat cervical spinal cord. Thus all animals will be implanted with identical hardware prior to being randomized into treatment groups to permit a direct comparison between optogenetic and electrical stimulation in Aim 2. We will use our established rat model of spinal contusion injury where animals are trained to perform precision forelimb reaching to accurately quantify recovery of function after injury. Our collaborative team has developed a reliable method of viral transduction of optogenetic proteins such that light-sensitive ion channels are expressed in neurons of the non-transgenic rat cervical spinal cord. Following 6-weeks of treatment with optogenetic and epidural electrical stimulation, we will explore the mechanisms by which each treatment leads to prolonged recovery of forelimb function in Aim 3. We will perform terminal electrophysiology and record the responses evoked by both optical and electrical stimulation in the same animals. Our preliminary data demonstrate an upregulation of axon growth following optogenetic stimulation. We will use retrograde trans-synaptic tracing and histology to quantify new circuit formation bypassing the injury. Labelled neurons will be co-localized with the neurons activated by optogenetic vs. epidural stimulation using combined in-situ hybridization and immunohistochemistry to illuminate mechanisms of recovery. In summary, we propose to uncover the mechanisms by which optogenetic spinal cord stimulation leads to nearly complete recovery of forelimb function following spinal cord injury. Once understood, we expect these mechanism to directly inspire treatments for a range of neurological traumas to the brain and spinal cord.
This research aims to advance the treatment for spinal cord injury by developing the technology and approach for delivering optogenetic stimulation to the cervical spinal cord to improve hand and arm function. We will then determine the mechanisms by which stimulation of the spinal cord leads to recovery of hand and arm function by comparing the cell types and neural circuits activated by optogenetic and electrical spinal stimulation.
