In the United States, there are approximately 2.5 million people with spinal cord injuries (SCIs). Depending on the location and severity of the injury, SCIs can result in long-term motor and sensory impairment. A very promising technology in neurorehabilitation for people with SCIs is transcutaneous spinal cord stimulation (tSCS). tSCS is a novel, non-invasive technique that stimulates the spinal cord through the surface of the skin. Recent clinical studies have already shown that tSCS is effective in helping to rehabilitate people with SCIs. However, while the rehabilitation method is sound, the physiological effects of tSCS on muscle recruitment are not well understood. Therefore, we are investigating the modulation of the spinal networks after the intervention with tSCS. Six patients with cervical SCIs underwent physical training paired with tSCS. Before and after training, SCS was used to induce motor evoked potentials which were measured with electromyogram. Evoked responses were extracted and analyzed by comparing peak to peak amplitude. After training and tSCS, both motor function and motor evoked potential amplitude increased, providing evidence that tSCS improves rehabilitation outcomes by modifying spinal networks. This research could lead to innovations in neural engineering and rehabilitation medicine and could greatly improve the quality of life for many people with SCIs.

Reactive astrogliosis is a condition where astrocytes, a type of brain cell, undergo morphological – shape - changes upon exposure to brain injury. Morphological changes of astrocytes are a key indicator of activation and can be beneficial in stopping initial brain injury effects, but chronic activation can drive glial scarring, which is detrimental for full recovery of normal brain function. Glial scarring has been linked to several diseases, including traumatic brain injury, Alzheimer’s Disease, and dementia. The purpose of this work is to quantitatively analyze the relationship between frequency and extent of reactive astrogliosis with relation to distance from the primary site of brain injury. My approach is to build a Python-based image analysis pipeline to quantify astrocyte cell features. The Nance Lab’s prior work using Python packages was effective in developing a pipeline to identify and quantify microglial - a different type of brain cell - shape properties. We are now building a pipeline to study astrocytes in brain slices from the injured preterm ferret brain, which were stained with an antibody for glial fibrillary acidic protein (GFAP). Images of cells at 20x magnification are provided by Dr. Tommy Wood. Since response to injury can be brain region and animal sex dependent, I analyze astrocyte cell features in each region of the brain from both sexes of ferrets. I used SciKit-Image along with other packages to segment, label, and quantify features of our cells, including perimeter, area, and circularity, among others. Expected results include a significant reduction in area and an increase in perimeter (larger surface-to-volume ratio) of cells that are closer to the injury. This image analysis pipeline will give us quantitative information about the cells morphology which are associated with biological markers that can be targets for future therapeutic treatment. Clear biological markers help researchers develop better treatment.

Motor injuries, such as stroke and spinal-cord injury, represent a significant public health burden, but often lack both cures and effective methods of symptom management. This has produced an urgent need for development of therapies that promote strengthening of injured neuronal pathways for restoration of critical functions, such as movement or sensation. Mechanisms that may induce synaptic plasticity are promising in their potential to augment weakened or injured pathways in the brain. This project aims to explore two such promising paradigms, targeted delivery of neuromodulators and closed-loop electrical stimulation, for potentiating cortical connections in a behaving macaque monkey. In the first experiment, I will be delivering a plasticity-enhancing neuromodulator, brain-derived neurotrophic factor (BDNF), to neurons in the motor cortex that fire in association with a wrist target-tracking motor task. BDNF has been shown to promote plasticity through inducing long-term potentiation, neuronal growth, axonal regeneration and re-myelination, and dendrite branching. Electrodes implanted at these sites will allow us to deliver stimulation to synaptically activate neurons to fire and test the strength of cortical connections, both in the presence and absence of BDNF, while the monkey performs the task. In the second experiment, I will explore an electrical-conditioning protocol to produce bidirectional spike-timing dependent plasticity in the same monkey. This will be achieved through paired intracortical microstimulation of two sites in the motor cortex, separated by a delay to produce synaptic changes. In both experiments, I will assess the effect of our intervention by measuring changes in the size and area of stimulation-evoked responses. We hypothesize that our interventions will result in significant potentiation of cortical connections. These results will inform how BDNF and electrical conditioning can modulate synaptic plasticity and strengthen neuronal connections.

Leigh syndrome (LS) is a progressive neurological disorder which often manifests within the first year of life and is characterized by the gradual loss of mental and movement abilities accompanied by epilepsy. LS has been associated with loss-of-function (LOF) mutations in genes that encode for proteins present in complex 1 of the electron transport chain. LOF mutations in one such gene, NADH dehydrogenase (ubiquinone) iron sulfur protein 4 (Ndufs4), are strongly associated with LS. Mice carrying a deletion of this gene exhibit symptoms similar to those found in humans, creating a relevant mouse model of LS. In this study, we investigated the effects of an Ndufs4 knockout on the neuronal excitability of both inhibitory and excitatory neurons located in different regions of the brain in LS mouse models. Two LS mouse models were generated by knocking out Ndufs4 in inhibitory or excitatory neurons utilizing LoxP/Cre technology. Mice carrying floxed alleles of Ndufs4 were crossed with VglutCre or GadCre driver mice. The progeny with excitatory or inhibitory neuron-specific Ndufs4 knockout and their control littermates obtained were perfused with phosphate buffered saline (PBS), then fixed with 4% paraformaldehyde (PFA). Brains from these mice were sliced and stained with c-Fos immunocytochemistry, then imaged to quantify neuronal activity. We hypothesize that neuronal excitability in both inhibitory and excitatory neurons will decrease after the Ndufs4 knockout, as mitochondrial defects would reduce the activity of both subsets of neurons. Findings from this study will potentially help understand the mechanisms for development of seizures in LS.

The hippocampus (HPC) and the lateral habenula (LHb) are two brain structures essential for flexible decision-making. The HPC enables navigation in complex environments by providing neural representations of space. The LHb encodes reward and aversion, and it also allows adaptive responding during hippocampal-dependent tasks. We hypothesize that the LHb and HPC communicate as an animal makes a decision. Specifically, we propose that they communicate via the coherence of single-unit activity in the LHb and oscillatory activity in the HPC, otherwise known as spike-phase coherence. We measured the neural activity of the LHb and HPC during a spatial delayed alternation task. We then calculated the temporal association between the spiking of individual neurons in the LHb and the oscillatory activity in the HPC. If the temporal association is stronger during a specific part of the task, it might indicate that the two structures are interacting within the same functional circuit to process relevant information. We expect to see stronger spike-phase coherence when a rat makes a decision, which would suggest that the network containing the LHb and HPC is becoming more engaged during the deliberation process. Overall, this work can expand our knowledge on the physiological interactions between the LHb and HPC in the context of decision making and adaptive responding. Our findings can ultimately contribute to the understanding of the mechanisms behind normal and pathological alterations in behavioral flexibility.