Sex differences in place learning on the Morris water task were examined in this dissertation. Adult Long Evans hooded rats were tested on this task to determine whether there are sex differences on this task, whether males and females use different strategies to solve the task, whether they attend to different aspects of the environment for navigation, as has been previously hypothesized, and whether they both use the fornix (hippocampal formation) for navigation on this task. Exploratory behaviors were also examined for both sexes to establish whether there was evidence that they engage in different activities while forming a cognitive map. Lastly, the role of the female estrous cycle on water maze performance was examined. Results indicated that males and females are equally impaired following fornix lesions, and there is no evidence that they use different strategies to solve the task or attend to different aspects of the environment. There was an overall sex difference in performance on the task, with males solving the task faster than females, and searching the target area at a much higher rate than females. There was some preliminary evidence of sex differences in exploration which predicted place learning in the water maze. Lastly, the estrous cycle did significantly effect the female's performance. Females in the high estrogen period were generally less efficient on the task than those in the low estrogen phase. This was interpreted to reflect a difference in motivation across the days of the cycle, rather than a difference in ability to perform the task.

The distribution and potential functions of extracellular matrix and cell-surface molecules during neural development were explored, using an insect olfactory system as a model. Immunocytochemical and biochemical experiments were performed to examine the cellular localization and temporal pattern of expression of molecules similar to the vertebrate extracellular matrix molecule tenascin. These studies showed that tenascin-like molecules were associated with glial cells that form borders around distinct units of neuropil called glomeruli. These molecules were present at critical times during the glomerulus formation. In vitro assays, performed to examine the effects of tenascin on the morphological development of moth CNS neurons, indicated that the growth of these neurons was inhibited by tenascin. Taken together, these results suggest that glial cells decorated with tenascin-like molecules could contribute to the patterning of the olfactory neuropil by constraining neurite outgrowth within developing glomeruli. The distribution of other glycosylated molecules that could play important developmental roles was examined using the lectin peanut agglutinin. This lectin labeled the tips of dendrites as they grow into developing glomeruli to interact with glial cells or sensory axons. Four lectin-labeled proteins were shown to be developmentally regulated and thus could participate in neurite outgrowth, synapse formation or the stabilization of glomerular units. Future experiments to further explore molecular mechanisms underlying the development of neural architecture are proposed. The results of this study are discussed in the context of dynamic interactions between neurons and glial cells.

The hippocampus is a brain structure known to be important for learning and memory, more specifically for the acquisition of spatial information. Hebb (1940) suggested that storage of information in the brain may involve modifications in the strength of synaptic connections. One example of an artificially-induced synaptic alteration that may share common mechanisms with memory formation is long-term synaptic enhancement (LTE). Recently, behaviorally-induced changes in hippocampal synapses have been discovered to occur in conjunction with exploratory behavior. This type of change has been called short-term exploratory modulation (STEM). It was proposed that STEM could share common mechanisms with artificially-induced LTE and memory formation in the hippocampus. The primary goals in this dissertation were to determine the relationship between STEM and LTE, to identify the mechanisms controlling these changes, and to determine whether STEM was a critical component of memory storage, a memory modulator, or an epiphenomenon. Synaptic changes in the hippocampus were measured by recording perforant-path evoked field potentials in the fascia dentata from awake behaving rats during rest and exploration or under sodium pentobarbital anesthesia. In the first experiment, a positive correlation was found between learning in the Morris swim task and STEM in young and aged rats. Comparisons of LTE and STEM indicated that STEM did not reflect the same type of synaptic change observed in LTE, such that the two phenomena did not interact with each other. Furthermore, the nature of the changes in the evoked potentials were observed to be different. Another feature that distinguishes STEM from LTE is that the induction of LTE is dependent on the NMDA receptor, whereas STEM is NMDA-receptor independent. When rats were anesthetized and their bodies warmed passively, they exhibited STEM-like changes which were highly correlated with body temperature. These temperature-induced changes in evoked potentials had little impact on the functional output of cells in the fascia dentata. It is therefore concluded that exploration-induced changes in the hippocampus are largely due to brain temperature changes and have minimal impact on the functioning of neurons as originally proposed.

The purpose of the study was to investigate the possible role of facial musculature movement in the subjective experience of emotion. Nineteen nondemented, nondepressed patients with idiopathic Parkinson's disease and 19 demographically matched control subjects were asked to rate valence and arousal dimensions after viewing emotionally laden slides. The patients with Parkinson's disease viewed one set of slides at their peak levodopa dose and one set of slides after at least a 12 hour abstention from their levodopa medication. Normal control subjects underwent two similar testing sessions, although no drug was administered. Mean valence and mean arousal ratings of slides within groups were determined. During the viewing of the slides, bilateral facial electromyographic activity in the zygomatic and corrugator muscle regions was recorded. EMG change scores relative to individual slide presentation were determined. Comparisons were made between and within groups of the mean valence, arousal, and EMG change scores relative to the slide valence type (i.e., positive, neutral, or negative slide content) and on/off drug condition. Results suggest that a subgroup of Parkinson's Disease patients experience similar emotional valence and arousal, to that of normal controls, when confronted with emotional visual stimuli. However, they display significantly less facial muscular movement in the zygomatic muscle region and somewhat less facial muscular movement in the corrugator region than the normal controls. Implications of these results are discussed relative to the James-Lange theory that posits emotional experience to be dependent upon a peripheral "feedback" system versus the Cannon-Bard theory that posits emotion to be mediated centrally. Although the present results lend support to the Cannon-Bard theory of emotion, future research is necessary to determine the role of the skin of the face (with blood and temperature components), rather than the facial musculature per se, in the subjective experience of emotion. It may be that the skin of the face and the sound of one's own voice (among other factors) play important roles in the subjective experience of emotion as posited by S. S. Tomkins. If so, a modified peripheral mediation theory of emotion would be supported.

<p>Emotions are pervasive in daily life, and a rich literature has documented how emotional stimuli and events disrupt ongoing processing and place heightened demands on control. Yet the executive control mechanisms that subsequently resolve that interference have not been well characterized. Although many failures of executive control have emotion at their core, numerous questions remain in the field regarding interactions between emotion and executive control. How do executive processes act on affective representations? Are emotional representations less amenable to control? Do distinct processes or neural networks govern their control? The present dissertation addresses these questions by investigating the neural systems and cognitive processes that support executive control in the face of interference from affective sources. Whereas previous research has emphasized the bottom-up impact of emotion on cognition, this dissertation will investigate how top-down executive control signals modulate affect's influence on cognition. Combining behavioral techniques with neuroimaging methodologies, this dissertation characterizes the interactive relationship between affective processes and top-down executive control and the ramifications of that interaction for promoting adaptive behavior.</p><p>Cognitive and behavioral phenomena related to affective interference resolution are explored in a series of research projects spanning attention and memory. Task-irrelevant affective representations may disrupt performance, but this interference appears to be dependent on top-down factors and can be resolved by executive mechanisms. Interference resolution mechanisms act on representations both of stimuli in the environment and information stored in memory. The findings reported here support emotion's capacity to disrupt executive processing but also highlight the role executive control plays in overcoming that interference in order to promote adaptive behavior.</p> / Dissertation

<p> To quote famous physicist and Nobel laureate, Dr. Richard Feynman, &ldquo;&hellip;everything that living things do can be understood in terms of the jigglings and wigglings of atoms.&rdquo; It is these jigglings and wigglings of atoms that form the focus of my dissertation, which studies the structural dynamics of two different allosteric proteins through computational simulations. Protein allostery is a field that has been investigated widely. But the structural details of how signals initiating at one site transmit through the network of residues in different proteins and result in the alteration of their functional states, still remains largely unresolved. Here, we independently study the kinesin motor protein and the neuromuscular acetylcholine receptor (nAChR) &ndash; both of which play crucial roles in cellular signaling. Kinesins are intracellular porters, carrying organelles, molecules and other cargo within the cell, while nAChRs are transmembrane receptors that aid in intercellular communication at nerve-to-muscle synapses. These two protein families are structurally and functionally very different, but both are allosteric in nature, with interesting protein dynamics that efficiently convert chemical energy to mechanical motions in order to perform their cellular functions.</p><p> The total timescale of an entire allosteric transition is currently too long for complete all-atom molecular dynamics simulations. Thus, in this dissertation, for both the projects, we begin at different equilibrium states of the proteins and carry out comparative analyses of conformation and dynamics at those states, which aids in elucidating the structural and functional correlates for these systems.</p><p> For the kinesin-microtubule (KIN-MT) system, we have built atomistic structure models for the key nucleotide-binding states of the kinesin-MT complex from lower resolution cryo-EM maps, by suitably modifying the MD potential with the EM map force. We have also studied ligand-protein (ADP/ATP-kinesin) interactions and predicted the sequence of structural changes in kinesin-MT complex during its conformational transitions between important biochemical states and pinpointed key contributing residues.</p><p> Simultaneously, we have also characterized the transmitter binding sites of neuromuscular acetylcholine receptors and analyzed the energy asymmetries between the fetal and adult endplate receptors. Through large-scale simulations of the fetal and adult binding sites, we have come across compelling evidence of the structural causes that explain these asymmetries and were successful in identifying the minimum construct that is both necessary and sufficient to exchange the function between adult and fetal binding sites in AChRs. Our <i> in silico</i> models and predictions act as important tools to further guide mutational and functional experiments.</p>

<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>

<p> <b>Purpose:</b> Sleep-disordered breathing (SDB) is a spectrum disorder that is estimated to effect a significant proportion of the pediatric population (1-3% in USA). SDB is able to disrupt and fragment sleep through frequent arousals and intermittent hypoxia. In addition, the long term effects of SDB in pediatrics have been well-documented; decreases in intelligence quotient (IQ), executive function, school performance, and alertness have all been observed. Although surgical treatments can be quite effective, there are no widely accepted prophylactic measures to prevent SDB development. Recently, breastfeeding duration in infancy has been demonstrated to be correlated with reduced SDB (lower AHI, RAI, and higher SpO2), as well as increases in IQ, executive function, and school performance (independent of SDB). The overarching goal of this dissertation was to examine the potential effects of both breastfeeding duration and SDB severity on the neurological underpinnings associated with observed behavioral and cognitive deficits; namely, correlations with white matter structural volume and fractional anisotropy (FA) scores through diffusion tensor imaging (DTI). Here, I proposed a unique developmental hypothesis where breastfeeding may ultimately reduce SDB, enabling the preservation of rapid eye movement (REM) sleep, and leading to healthier neurological white matter development. </p><p> <b>Method:</b> Twenty-four children with SDB and 19 healthy controls were imaged using MR techniques. White matter volume was measured using the central 13 millimeters of the corpus callosum (CC). DTI of major white matter tracts was also conducted. The SDB group received neurocognitive testing to assess cognitive performance; the control group was assessed using real-world academic report cards. Finally, REM sleep was quantified in infants using overnight polysomnography (PSG), with SDB metrics and infant feeding method also measured. Results: There was no correlation between infant feeding methods and CC volume in either group, nor a significant differences between CC volumes in children with SDB versus those without. However, increased breastfeeding duration was correlated with increased left superior longitudinal fasciculus (LSLF) and left angular bundle (LAB) FA scores in healthy controls. In 8-9 month old infants, increased breastfeeding duration was also correlated with a reduced proportion of REM sleep (%TST), and children with exclusive breastfeeding had reduced SDB in infancy compared to children with any formula feeding. Finally, exclusively formula-fed infants were diagnosed with &ldquo;primary snoring&rdquo; more often than those with any amount of breastfeeding. </p><p> <b>Conclusions:</b> The findings in this dissertation revealed associations between breastfeeding, SDB, REM sleep, and white matter integrity in the brain. These results support the hypothesis that certain cognitive effects associated with SDB and infant feeding methods may have common underlying anatomical brain changes that subserve these observed phenomena.</p>

<p> Alzheimer&rsquo;s disease (AD) is the leading cause of dementia, accounting for 50 to 80 percent of dementia cases, and the prevalence of the disease is projected to increase significantly with time. AD is characterized by severe cognitive decline with age, ultimately requiring continued caregiving and eventually death. The pathology of AD is characterized by the presence of extracellular amyloid plaques, intracellular neurofibrillary tangles (NFT) composed of hyperphosphorylated tau protein, neuron loss, and evidence of inflammation indicated by the presence of reactive microglia and astrocytes. Frontotemporal Lobe Dementia (FTLD) is a rare form of dementia that is related to AD, most notably in the pathology of hyperphosphorylated tau and macroscopic brain shrinkage. It has been defined as one of a host of tauopathies, and has a more rapid onset than AD. Symptoms that resemble personality changes, moreso than memory loss, are characteristic of these other tauopathies (FTLD is a representative of a whole class of neurological disorders). Like AD, there are no known treatments or cures for FTLD. AD and FTLD are two manifestations of a class of diseases known as tauopathies, due to the presence of toxic forms of tau. </p><p> Tau is a protein normally found in neurons. It functions as a stabilizer for microtubules, and has a role in the trafficking of materials from the cell body to the presynaptic terminal. In AD and FTLD, tau can become hyperphosphorylated, which causes it to form twisted fibrils called NFTs. An emerging area of research is to identify antibodies that target tau as a way to clear tau pathology and hopefully reduce synaptic and neuron loss (Boutajangout et al., 2011b). While these diseases have no known cure or treatment at present, immunotherapy is emerging as a promising approach for treatment. The studies presented here investigated a variety of antibodies directed against tau, and incorporated different timeframes and administration routes to identify the best candidate for future clinical investigation of tau immunotherapy. </p><p> The mouse model rTg4510, known for expressing cognitive-related tauopathy, was primarily used to evaluate tau antibody effectiveness prior to clinical consideration. Our investigations began by utilizing a more familiar mouse which was also reported to express tau pathology. </p><p> Our studies first examined intracranial injection of a variety of antibodies using a mouse model previously reported to demonstrate tau pathology, to identify short-term clearance of tau pathology and NFTs. Next, we examined a more robust tau-producing mouse line, to further identify a most effective antibody, as well as to examine the time course of effect, after administration. A longer-term administration, and different route of administration was tested using mini-osmotic pump implantation into the mice, which provided for 28-day continuous infusion. This approach was followed with administration of antibodies, systemically. Behavioral analysis, in addition to pathological testing, was incorporated into the longer-term administration studies.</p>