Thank you. Next speaker is Dr. Condyles, Electrical Stimulation in White Matter Following Spinal Cord Injury in Rats. Now for something completely different. I'd like to thank the organizers for inviting me here to speak today. I'm going to be describing work from my graduate studies in the labs of Steve Perlmutter and Phil Horner regarding electrical stimulation and potential benefits for white matter modeling after spinal cord injury. So this work will hopefully contribute to a body of literature that explores potential therapeutic effects for electrical stimulation in a spinal cord injury in terms of improving outcomes and motor behavior. In particular, in our lab, we are also interested in spinal cord injury-induced demyelination and the natural remyelination that might occur in rodent models and how electrical stimulation might tap into that system and promote it. For my work, this involves corticospinal tract stimulation, and specifically I'm assessing remodeling of the corticospinal tract after injury in terms of axonal branching and survivability and also the demyelination, potential remyelination that might occur in terms of numbers of myelin sheaths, numbers of ligand endocytes, and the numbers of bare and remyelinated or demyelinated axons. This is done by inducing a C4 hemi-contusion injury in the dominant side of the forelimb or of spinal cord, excuse me. And then one week later, we implant stimulating electrodes into layer five of the motor cortex with the idea that we can then stimulate the corticospinal tract specific to invoke forelimb movement. We also inject a tracer so we can not only map the axons that we've stimulated, but we also have an idea of surviving axons. Animals undergo three weeks of stimulation, and then we also have a smaller cohort that is pulled out after one week, and RNA is purified in order to get an idea of transcriptome changes that might be driving histological changes that we see after three weeks. We do RNA purification from five regions, but I'll be focusing on analyses from the subcortical white matter on the stimulated, beneath the stimulated motor cortex. If we look at this heat map of a number of candidate genes that are involved in node of Ranvier maintenance and function, blue represents a decrease in expression, whereas yellow an increase. And in comparing those five regions, the subcortical white matter on the stimulated side shows a decrease in downregulation in a number of these candidate genes involved in node of Ranvier function and maintenance. This led us to wonder if potentially this decrease in expression might lead to a morphological change that might include a decrease in the number of nodes of Ranvier in the corticospinal tract after stimulation. To analyze this, we went into the spinal cord and looked in cross-section. And here we can see within the box the corticospinal tract. And then if we look at a histograph or an image of the corticospinal tract in our rats, you can see that the surviving axons are marked in green and nodes of Ranvier are marked in blue. And the blowout, even below, the colors are switched, but green, again, denotes the surviving axons. And pink, you can see co-localized with some of the surviving axons. These data are preliminary, but an initial quantification shows that if you look at the co-localized nodes on the BDA-positive axons, normalized for the total number of BDA-positive axons, stimulated animals have fewer nodes of Ranvier on those surviving axons. Again, these are preliminary data, but are potentially pretty promising. When we consider what white matter plasticity actually might entail, there's a number of different possibilities. It might be the myelination of previously bare axons, as in figure A, or the change of a myelin sheath in figure B to either lengthen or shorten or thicken. But we believe, potentially, we are tapping into what might be going on in figure C. An axon has two myelin sheaths, which have been potentially destroyed by the injury, so demyelination. And an oligodendrocyte matures and forms a new myelin sheath. The myelin sheath might cover that same level of axon, or same amount of axon, but would account for the decrease in the number of nodes that we see. Again, these are preliminary, and further work is needed, but we have promising evidence that stimulation might reduce the number of nodes of Ranvier on corticospinal tract following an injury. This is supported by RNA evidence, as well as histological evidence, and future analyses are going to definitively say whether or not this decrease in the number of nodes is, in fact, a result of longer myelin sheaths. In addition, future analyses are going to delve into the functional improvement that might go along with these morphological changes. We'll skip this, and I will say thank you.

electrical stimulation

white matter modeling

spinal cord injury

corticospinal tract

axonal branching