Spinal cord injuries cause damage to the corticospinal tract which can lead to deficits in coordination and movement. This greatly alters and may decrease an individual’s quality of life. This project utilizes optogenetics to trigger action potentials in neurons, and tests the hypothesis that activity can promote regeneration of corticospinal connections. Co-cultured mouse spinal and cortical neurons serve as an in vitro model system. The spinal and cortical neurons are in separate chambers that are connected by a canal. Cortical cells are transfected with light- activated channels and stimulated with LED lights to trigger action potential firing. The canal connecting the chambers allows for the cortical neurons to form new synapses with the spinal neurons. In order to quantify the results, synapsin, a protein found in presynaptic vesicles, is labelled using immunocytochemistry, allowing us to quantify the number and size of synapses by measuring synapsin-positive puncta. It is expected that cells stimulated with light will show a greater number of synapses compared to those that were not. Different patterns of neuronal stimulation are tested to determine the best parameters for promoting synapse regeneration and strengthening. Once these have been determined, they will be validated in an in vivo rodent model, prior to testing in primates.

Vagus nerve stimulation (VNS) involves the delivery of electrical stimuli to the vagus nerve, which is associated with several brain regions and functions. VNS is currently used as auxiliary treatment for some types of epilepsy and there is significant interest regarding its potential in the treatment of other illness as well as for cognitive augmentation and promoting plasticity. The goal of this project is to investigate the differences in ipsilateral and contralateral cortical responses to different vagus nerve stimulation protocols, as well as to compare the responses to invasive versus noninvasive VNS delivery methods. Data was collected from a non-human primate using dual electrodes (with epicortical and intracortical contacts) placed in the prefrontal, premotor, supplementary and primary motor and parietal cortical areas, as well as a nerve cuff placed on the left trunk of the vagus nerve. Data analysis focused on the cortical evoked potentials elicited by VNS and recorded at cortical sites both ipsilateral and contralateral to the VNS. VNS was delivered to both the auricular branch of the vagus nerve in the noninvasive protocol and through a nerve cuff on the left vagus nerve trunk for the invasive protocol. This work is related to a larger project focused on establishing protocols for noninvasive VNS to augment targeted neuroplasticity and enhance cognitive performance in normal nonhuman primates. This nonhuman primate study will be directly applicable to the development of noninvasive VNS technology that can be used to enhance neuroplasticity and cognitive performance in healthy adult humans.

Cortical plasticity is the substrate for learning and memory. It is the basis of an organism’s ability to adapt in response to a changing environment and is central to functional recovery after an injury involving the nervous system. Vagus nerve stimulation (VNS) has already been shown to be effective in altering neuroplasticity. Most VNS research has been conducted on epileptic animals and thus offers little information on how VNS may affect a healthy human brain. The final goal of this project is to establish a minimally invasive VNS protocol aiming to augment neuroplasticity and enhance behavioral performance in a cognitive task. Non-human primates are implanted with cortical electrodes and also receive a stimulating cuff electrode around the vagus nerve in the neck. By delivering current through the cuff, vagal evoked potentials (VEPs) are elicited on the cortex. In order to measure how VNS affects cortical excitability, we pair the stimulation of the vagus nerve with stimulation of a somatosensory nerve (i.e. median nerve) and we quantify the effects on the cortical activity by measuring the magnitude of the evoked responses generated on the cortex. Preliminary results from one animal showed a suppression of cortical activity in the primary motor area (M1) when the delay between the vagus stimulation and the median nerve stimulation ranges between 100 and 150 msec. Four additional animals have received vagus nerve cuffs and neural implants targeting multiple cortical areas. These neural implants give us access to recording not only from M1, but also from prefrontal, premotor, supplementary, and parietal cortical areas. In this way we will be able to characterize the physiological effects of VNS on the cortical excitability of different brain areas, generating data and insights never before obtained and directly applicable to the development of neuromodulation technology in humans.

Spinal cord injury (SCI) is a debilitating disease with few treatment options available for recovering motor function. Based on past studies using electrical stimulation of the spinal cord, we believe that long-term optogenetic spinal stimulation (OSS) may improve motor function after an SCI. We are investigating this therapeutic potential using a rat model of SCI with an implantable LED to deliver optogenetic stimulation in vivo. However, activation of the LED produces heat that could damage the surrounding tissue. I have modified these LED implants by incorporating a thermistor that tracks temperature changes during optical stimulation. Using this device, I determined how the modulation of stimulation parameters affects heat production at the site of the implant and have identified several safe parameter sets. These results will inform the parameter choices used in future studies on OSS. An optimized OSS methodology has the potential to improve the lives of those with an SCI by enhancing their capability for volitional movement.

The research project primarily aims at better characterizing how neurons of certain types transform their inputs from “upstream” neurons into outputs to “downstream” neurons. So far in the project, it has been determined that there are major differences between Intratelencephalic (IT) and Pyramidal Tract (PT) neurons on the basis of genetics, morphology, electrophysiology and functionality. We have collected data from two genetically distinct mice. Single cell recordings reveal that PT and IT type neurons are electro physiologically different, in both the locations to which they send their signals in the nervous system and the neuron morphology. Using retrograde tracing (a research method used to trace neural connections), it was found out that PT type send their axons to spinal cord and regions outside of telencephalon region of the brain but IT were restricted to telencephalon region of the brain. Now, my primary focus will be to elucidate how the electrophysiological and morphological characteristics interact. To do this, I will use reconstructions from two photon imaged stacks of their structure imported into a simulation environment called NEURON. Using NEURON, I will try to identify the potential mechanisms that underlines the sensitivity in synaptic integration of the two neuron types. This will provide testable hypothesis for future experimentation. IT and PT type have distinct roles. IT type are sensitive to anti-depressing mechanisms whereas PT type are sensitive to ALS mechanisms. It is this property that will help us create targeted medications.