<p> Neurons in human somatosensory cortex are somatotopically organized, with sensation from the lower limbs mediated by neurons near the midline of the brain, whereas sensations from the upper body, hands and orofacial surfaces are mediated by neurons located more laterally in a sequential map. Neurons in Brodmann's area (BA) 3b are exquisitely sensitive to tactile stimulation of these skin surfaces. Moreover, the location, velocity and direction of tactile stimuli on the skin's surface are discriminable features of somatosensory processing, however their role in fine motor control and passive detection are poorly understood in health, and as a neurotherapeutic agent in sensorimotor rehabilitation. To better understand the representation and processing of dynamic saltatory tactile arrays in the human somatosensory cortex, high resolution functional magnetic resonance (fMRI) is utilized to delineate neural networks involved in processing these complex somatosensory events to the glabrous surface of the hand. </p><p> The principal goal of this dissertation is to map the relation between a dynamic saltatory pneumatic stimulus array delivered at 3 different velocities on the glabrous hand and the evoked blood-oxygen level-dependent (BOLD) brain response, hypothesized to involve a network consisting of primary and secondary somatosensory cortices (S1 and S2), insular cortex, posterior parietal cortex (PPC), and cerebellar nuclei. A random-balanced block design with fMRI will be used to record the BOLD response in healthy right-handed adults. Development of precise stimulus velocities, rapid rise-fall transitions, salient amplitude, is expected to optimize the BOLD response.</p>

<p> New evidence afforded by advanced live-tissue imaging techniques indicates that astrocytes, the predominant glial cell subtype, play a far more active role in synaptic physiology than was previously appreciated. Evolved iterations of genetically encoded calcium indicators, primarily the GCaMP variants, have enabled high spatiotemporal resolution detection of intracellular activity, but are limited by few options for gene transfection and expression. The goal of this dissertation work was to develop novel GCaMP-based tools for straightforward optical interrogation of astrocytic activity in rodent models of neuropathology. </p><p> A Polr2a-targeted, Cre-dependent, CAG-driven, GCaMP5G-expressing reporter mouse line was constructed and designated &ldquo;PC-G5-tdT&rdquo;. Detection of positive cells was facilitated by an IRES-tdTomato tag. PC-G5-tdT proved effective in diverse developmental contexts and reported intracellular calcium dynamics in somas and fine processes of astrocytes, microglia and neurons. Electrophysiological and behavioral analyses failed to detect a detrimental impact of GCaMP5G expression on nervous system performance. In acute brain slices prepared from a model of endotoxemia-induced neuroinflammation, a stereotyped sequence of astrocytic intrinsic activity was observed over the acute phase. At early time points, frequent somatic and distal process transients were observed but progressively declined with process event frequency lagging behind the soma.</p><p> Several rat models of human neuropathology provide systems for researching basic mechanisms of disease. Unfortunately, transgenic rat technologies are immature and viral-based methods are hampered by side effects. <i>In utero</i> electroporation (IUE) is a proven method for transfecting astrocytes and neurons without major drawbacks. A toolset of IUE plasmids carrying CAG-driven, subcellular compartment-targeted GCaMP variants with optional cytosolic tdTomato co-expression was constructed. Stable expression was accomplished via random genomic integration of the reporter cassette through a binary plasmid system derived from the <i>piggyBac</i> transposon. Preparation- and age-specific patterns of activity were readily detected in astrocytes and neurons. In particular, organotypic slice culture astrocytes exhibited frequent global intrinsic transients whereas activity was restricted to distal astrocytic processes in acute brain slices prepared from older animals.</p><p> This work has already stimulated progress in the field of glial cell physiology. Future application of these tools will advance our understanding of glial-neuronal interaction and possibly inform development of improved disease modification strategies.</p>

Thesis (Ph.D.)--Syracuse University, 2008. / "Publication number: AAT 3323042."

Thesis (PH.D.)--Syracuse University, 2003. / "Publication number AAT 3081645."

<p> Using tools, writing, and eating are all important behaviors that involve manipulating objects. Successful manipulation requires the control of both the force exerted on the object and its resultant motion. Both have been associated with neural activity in the motor cortex and we are interested in the extent to which neural firing rates in this brain region are related to their combined control. The mechanical relation between force and motion is impedance and we hypothesized that motor cortical activity encodes an impedance signal that reflects the force and motion demands of behavior. We examined this possibility with a paradigm in which subjects manipulated a handle that moved along a track. The handle was locked in place until the subject exerted enough force to cross a specific threshold; it was then released and moved along the track. We hypothesized that this ballistic-release task would encourage subjects to modify their arm impedance in anticipation of the upcoming movement. </p><p> We modeled the behavior as a physical dynamical system and found that one component of model impedance, stiffness, varied in a way that matched the behavioral demands of the task and that stiffness could be dissociated from changes in force and displacement. We recorded activity from a population of motor cortical neurons and found that the temporal and time-averaged neural responses encoded information about motion and force. We also could decode model impedance parameters that we then used to approximate the time-varying force exerted on the handle. The force exerted on the handle and the model stiffness depended on muscle activity and we found components of muscle activity related to both force and model stiffness. Additional components of motor cortical activity were also related iv to both force and stiffness, suggesting a possible parceling of muscle-related representations in motor cortical activity. In addition to extending current models of neural activity to include manipulations, this study may be helpful in understanding how information encoded in motor cortical activity might be transformed into muscle activity during object interaction.</p><p>

<p> In the past couple of decades we have seen remarkable advances in the integration of biological systems with artificial ones. Our knowledge of both of these worlds has grown exponentially, and in particular our knowledge of the human body. In recent years we have been able to understand and treat diseases we never thought we would, and we have even been able to interface with the body to restore lost functions. Direct interaction with the human brain to read and write information to it has been achieved thanks to the development of neural probes. The work presented in this thesis focused on improving the performance of such probes in regards to their operational lifetime. This work begins with a description and demonstration of how silicon carbide technologies are suitable and compatible with neural probes, and is a better material choice for device insulation. Then, a fabrication method for silicon carbide based electrode arrays is presented, in which conductive silicon carbide is integrated with insulating silicon carbide to form an electrode architecture in which the only exposed material is the superior silicon carbide. Following this, <i>in-vivo</i> demonstration of these silicon carbide based electrode arrays is done by recording from the nervous system of an animal model</p><p>

<p> Pupil size is controlled by the autonomic nervous system, and iris behavior reflects a balance of input from both the sympathetic and parasympathetic nervous systems. The pupillary light reflex (PLR) occurs in response to light entering the eye and requires functional integrity of the retina and specific nuclei of the midbrain. Recently, pupillography or quantitative analysis of the PLR has been developed as a non-invasive, objective technique capable of detecting subtle changes associated with the complex network of neuronal circuitry involved in modulating pupil size. This makes the PLR a useful biomarker that can be used to monitor disease progression in neurological disorders. </p><p> The neuronal ceroid lipofuscinoses (NCLs) are a group of lysosomal storage disorders that are inherited in an autosomal recessive manner. A late-infantile onset form of NCL (CLN2) is caused by a mutation in the <i>CLN2</i> gene which codes for tripeptidyl peptidase-1 (TPP1), a soluble, lysosomal enzyme that aids degradation of peptides in cells throughout the body. A Dachshund model of CLN2 was developed and is currently being maintained at the University of Missouri. Dogs affected by CLN2 lack functional TPP1 and present with progressive ataxia, cognitive and behavioral changes, and myoclonic seizures starting at approximately 7-8 months of age and progressing to a terminal state requiring euthanasia at 10 to 11 months of age. In addition, affected dogs exhibit vision loss and marked deficits in ERG b-wave amplitude and significant thinning of the inner retina by disease end-stage. The strong resemblance to the human CLN2 makes these dogs an excellent model in which to test possible treatment options prior to beginning human clinical trials.</p><p> In the effort to make optimal use of the canine model of CLN2, studies were undertaken to develop a reliable protocol for the quantitative assessment of the canine PLR. Using the developed equipment and methodology, we thoroughly evaluated the PLR in response to short flashes of white light of increasing intensity in normal and CLN2-affected dogs. We found that CLN2-affected dogs exhibit PLR deficits that progress with age and other symptoms of disease. Deficits are particularly apparent with dim stimuli and likely result from a combination of decline in retinal function and disease related changes in areas of the midbrain involved in modulating the PLR.</p><p> In the Dachshund CLN2 disease model, it was previously shown that administration of recombinant TPP1 via infusion into the cerebrospinal fluid (CSF) results in widespread distribution and uptake of the active enzyme into many structures of the brain and in reduction in the accumulation of neuronal lysosomal storage material that is characteristic of this disease. Studies were undertaken to determine if TPP1 enzyme replacement therapy (ERT) could ameliorate PLR deficits associated with CLN2. One-third of the dogs treated with ERT exhibited a substantial delay in the appearance of PLR deficits compared with untreated, affected dogs. However, no improvements in retinal function could be measured by the ERG. It is unlikely that TPP1 reached the retina, and it is more likely that ERT normalized the PLR by preventing degeneration in areas of the midbrain involved in modulating the PLR. However, further analysis of retinal and midbrain tissues is necessary to fully explain these treatment effects.</p><p> The characterization of disease-related alterations in light induced responses contributes to our understanding of the pathology underlying CLN2. Preventing development of the deficits in the PLR and ERG responses can be used to objectively assess the efficacy of therapeutic interventions for CLN2 that are currently being evaluated. An ideal therapy would prevent the declines in both the PLR and the ERG responses by preventing both retina and brain degeneration.</p><p>

Thesis (Ph. D.)--University of Toronto, 2008. / Includes bibliographical references.