<p> The role that myeloid innate immune cells play in neurodegeneration has long fascinated researchers because of the apparent changes of these cells found in all neurodegenerative diseases. However, it has become clear that the different parts or compartments of a neuron that traverse different anatomical environments degenerate at different times. Since there are myeloid cells around all of these neuronal compartments, answering the question of how myeloid cells impact the process of compartmentalized neurodegeneration is challenging. Further complicating this question is the fact that these cells can rapidly change their morphology and function in a process termed activation. In these activated states, myeloid cells have the capacity to regulate many aspects of neuronal damage and repair. Lastly, these myeloid cells are derived from different lineages that may play different roles in neurodegeneration. </p><p> Many authors have manipulated myeloid cells by loss of the receptor (CX3CR1) for the chemokine fractalkine and arrived at contrasting and context-dependent results even within models of the same neurodegenerative disease. Few studies have examined loss of fractalkine signaling in multiple compartments and even fewer have collected these data for each animal. Therefore, it remains unknown how loss of fractalkine signaling affects compartmentalized neurodegeneration. </p><p> Since the chronic mouse model of glaucoma, the DBA/2J, grants easy access to different degenerating retinal ganglion cell (RGC) compartments, it is an ideal system to determine how myeloid cells affect neuronal compartmentalized degeneration. The DBA/2J also features changes to myeloid cells, including microglial activation as early as 3 months and macrophage infiltration at 10 months. We generated DBA/2J mice lacking CX3CR1, and determined that this differentially affected RGC compartmentalized degeneration by increasing numbers of RGCs with a marker of disrupted axonal transport while not affecting RGC transcriptional dysregulation or optic nerve degeneration. Loss of CX3CR1 did not increase microglial activation overall but increased macrophage infiltration. However, numbers of infiltrating macrophage did not correlate with RGC pathology. We found that early microglial activation was composed of resident microglia and that high levels correlated strongly with later optic nerve degeneration. All together, these data implicate the resident microglia in disease progression in neurodegeneration.</p>

<p> The brain's reward circuitry is critically involved in regulating mood-related behaviors such as depression and aggression. However, we currently possess a remarkably limited understanding of the molecular and circuit based mechanisms that govern how these reward systems are subverted in neuropsychiatric disorders. We, and others, have previously shown that the nucleus accumbens (NAc), a key hub within the reward system, is a critical regulator of social reward behaviors. This dissertation will explore the two separate, but intrinsically connected, social behavioral states of depression and aggression, and in turn attempt to elucidate putative intracellular and circuit based mechanisms that govern how the NAc modulates these behaviors. Through the use of social defeat stress, in which an aggressive dominant mouse antagonizes a non-aggressive submissive mouse, we can identify the mechanisms that govern both the development of depression-like behaviors (in the subordinate mouse) and the motivation to attack (in the dominant mouse). Specifically, in Chapter 1, I will present an introduction on reward circuitry and synaptic plasticity. In Chapter 2 I will detail the animal model, chronic social defeat stress, which we use to study both depression and aggression-like behaviors in mice. In Chapter 3 I will present data on the role of structural plasticity within the nucleus accumbens, governed by epigenetic regulation of small RhoGTPase Rac1 transcription, on driving the development of depression-related behaviors and social avoidance. In Chapter 4, nucleus accumbens projections to the lateral habenula will be shown to play a critical role in governing the motivational component of aggressive behavior. Lastly, in Chapter 5 I will present future directions for both projects. Although this dissertation presents data spanning both depression and aggression-related behavioral domains, one clear commonality is that the NAc functions as a critical integrator of reward-related social behaviors, and understanding the mechanisms guiding this plasticity may help to establish novel therapeutic strategies for treating mood-related disorders.</p>

<p>Numerous studies have explored brain activities in relation to timing behaviors from spike firing rates to human neuroimaging signals; however, not many studies have explored functional relations between neural oscillation and timing behavior. Neural oscillations are recently being considered as a fundamental aspect of brain function that modulate broad ranges of cognitive processes. Striatal-beat frequency model (SBF) also proposed that oscillatory properties of neurons are the critical feature that underlies timing behavior. In order to reveal the functional relations between neural oscillations and timing behavior, multiple timing paradigms have trained in groups of rats, and the neural oscillatory patterns during the timing tasks were recorded and analyzed. More specifically, oscillatory patterns that are involved in duration encoding and comparison have been identified using ordinal temporal comparison task. Then, the patterns of theta and delta rhythms have been explored in relation to duration judgment and production. Also, oscillatory patterns underlying interval timing have been compared to the patterns of working memory. The major target areas for those electrophysiological experiments were the cortical-striatal circuits which known for their critical role in timing behavior. Finally, excitatory and inhibitory oscillators (EIO) model has been proposed in order to address oscillatory features underlying interval timing and working memory.</p> / Dissertation

<p>Abstract ART AS NEURONARRATIVE IN LIMINAL EXPERIENCE Brenda Elliott Saybrook University This study used arts-based and narrative inquiry to explore how artists express subjectively felt liminal experience in the process of art-making. The term liminal comes from the Latin limen, meaning threshold, and can be defined as an in-between, limbo, or suspension between two more relatively stable states in persons, places, or things. Transition through the liminal state contains the potential of change. Although the process of change within the human experience has been widely studied, the mechanisms of change, the means by which change occurs, has received relatively little attention. Fourteen artists were interviewed about their use of art as a means to deal with what they have felt to be liminal experiences. Interviews included direct observation of the artwork, descriptions of the art process, reports of subjective experience of art-making, the artist's writing and journaling of the art process, and the context of the art-making within the life of the participant. The interviewed focused on two main topics: 1. The artist's subjective descriptions of the liminal experience, including his or her major concerns throughout the experience; 2. The artist's description of how he or she dealt with the experience of liminality through art-making and attempted to resolve those concerns. The comparative analysis technique of grounded theory was used to generate conceptual categories and their properties from evidence provided directly from interview data, to generate a basic social psychological process. For the artists interviewed, meaningful and satisfying self-creation was archived in their art process. Anticipatory platforming, the beginning of creation of renewed identity, emerged as a basic social psychological process. Anticipatory platforming finds its place within autopoeisis, the principle of self-generation of an organism as demonstrated in dynamical systems. The concept of anticipatory platforming may prove significant for psychotherapists who are challenged to find ways to support people dealing with change and uncertainty in an increasingly stressful world. It is proposed that an affectively attuned and body-based anticipatory platform facilitates a framework for a transformed self, through which the threshold of change is supported.

<p>Integrating information from multiple sources is a crucial function of the brain. Examples of such integration include multiple stimuli of different modalties, such as visual and auditory, multiple stimuli of the same modality, such as auditory and auditory, and integrating stimuli from the sensory organs (i.e. ears) with stimuli delivered from brain-machine interfaces.</p><p>The overall aim of this body of work is to empirically examine stimulus integration in these three domains to inform our broader understanding of how and when the brain combines information from multiple sources.</p><p>First, I examine visually-guided auditory, a problem with implications for the general problem in learning of how the brain determines what lesson to learn (and what lessons not to learn). For example, sound localization is a behavior that is partially learned with the aid of vision. This process requires correctly matching a visual location to that of a sound. This is an intrinsically circular problem when sound location is itself uncertain and the visual scene is rife with possible visual matches. Here, we develop a simple paradigm using visual guidance of sound localization to gain insight into how the brain confronts this type of circularity. We tested two competing hypotheses. 1: The brain guides sound location learning based on the synchrony or simultaneity of auditory-visual stimuli, potentially involving a Hebbian associative mechanism. 2: The brain uses a ‘guess and check’ heuristic in which visual feedback that is obtained after an eye movement to a sound alters future performance, perhaps by recruiting the brain’s reward-related circuitry. We assessed the effects of exposure to visual stimuli spatially mismatched from sounds on performance of an interleaved auditory-only saccade task. We found that when humans and monkeys were provided the visual stimulus asynchronously with the sound but as feedback to an auditory-guided saccade, they shifted their subsequent auditory-only performance toward the direction of the visual cue by 1.3-1.7 degrees, or 22-28% of the original 6 degree visual-auditory mismatch. In contrast when the visual stimulus was presented synchronously with the sound but extinguished too quickly to provide this feedback, there was little change in subsequent auditory-only performance. Our results suggest that the outcome of our own actions is vital to localizing sounds correctly. Contrary to previous expectations, visual calibration of auditory space does not appear to require visual-auditory associations based on synchrony/simultaneity.</p><p>My next line of research examines how electrical stimulation of the inferior colliculus influences perception of sounds in a nonhuman primate. The central nucleus of the inferior colliculus is the major ascending relay of auditory information before it reaches the forebrain, and thus an ideal target for understanding low-level information processing prior to the forebrain, as almost all auditory signals pass through the central nucleus of the inferior colliculus before reaching the forebrain. Thus, the inferior colliculus is the ideal structure to examine to understand the format of the inputs into the forebrain and, by extension, the processing of auditory scenes that occurs in the brainstem. Therefore, the inferior colliculus was an attractive target for understanding stimulus integration in the ascending auditory pathway.</p><p>Moreover, understanding the relationship between the auditory selectivity of neurons and their contribution to perception is critical to the design of effective auditory brain prosthetics. These prosthetics seek to mimic natural activity patterns to achieve desired perceptual outcomes. We measured the contribution of inferior colliculus (IC) sites to perception using combined recording and electrical stimulation. Monkeys performed a frequency-based discrimination task, reporting whether a probe sound was higher or lower in frequency than a reference sound. Stimulation pulses were paired with the probe sound on 50% of trials (0.5-80 µA, 100-300 Hz, n=172 IC locations in 3 rhesus monkeys). Electrical stimulation tended to bias the animals’ judgments in a fashion that was coarsely but significantly correlated with the best frequency of the stimulation site in comparison to the reference frequency employed in the task. Although there was considerable variability in the effects of stimulation (including impairments in performance and shifts in performance away from the direction predicted based on the site’s response properties), the results indicate that stimulation of the IC can evoke percepts correlated with the frequency tuning properties of the IC. Consistent with the implications of recent human studies, the main avenue for improvement for the auditory midbrain implant suggested by our findings is to increase the number and spatial extent of electrodes, to increase the size of the region that can be electrically activated and provide a greater range of evoked percepts.</p><p>My next line of research employs a frequency-tagging approach to examine the extent to which multiple sound sources are combined (or segregated) in the nonhuman primate inferior colliculus. In the single-sound case, most inferior colliculus neurons respond and entrain to sounds in a very broad region of space, and many are entirely spatially insensitive, so it is unknown how the neurons will respond to a situation with more than one sound. I use multiple AM stimuli of different frequencies, which the inferior colliculus represents using a spike timing code. This allows me to measure spike timing in the inferior colliculus to determine which sound source is responsible for neural activity in an auditory scene containing multiple sounds. Using this approach, I find that the same neurons that are tuned to broad regions of space in the single sound condition become dramatically more selective in the dual sound condition, preferentially entraining spikes to stimuli from a smaller region of space. I will examine the possibility that there may be a conceptual linkage between this finding and the finding of receptive field shifts in the visual system.</p><p>In chapter 5, I will comment on these findings more generally, compare them to existing theoretical models, and discuss what these results tell us about processing in the central nervous system in a multi-stimulus situation. My results suggest that the brain is flexible in its processing and can adapt its integration schema to fit the available cues and the demands of the task.</p> / Dissertation

<p>Postnatal subventricular zone (SVZ) neurogenesis in the rodent generates large numbers of neuroblasts that migrate and integrate daily into the mature olfactory bulb (OB) circuit. After brain injury and stroke, neural stem cells (NSCs) within the SVZ niche generate neuroblasts that migrate to the site of injury, thus providing a potential endogenous source of cells to replace those lost from injury. Given the paucity of treatment options after stroke, it is widely believed in the field that enhancing neurogenesis after injury has promise for providing future treatment. Despite the promise of endogenous NSCs for repair, in health the degree to which SVZ neuroblasts have the capability to integrate outside of their normal development in the olfactory bulb (OB) remains an open question. After brain injury, the progeny produced by NSCs after stroke remains poorly understood. My research has focused on identifying the NSC response to injury, and modeling SVZ neuroblasts' intrinsic integration capabilities. </p><p>Using nestin-CreERtm4 NSC lineage tracing we identified that NSCs produce a specialized Thbs4hi population of astrocytes. Photothrombotic cortical injuries result in Thbs4hi astrocyte generation, rather than neuroblast production in NSCs. In Thbs4KO/KO mice SVZ astrogenesis is ablated with neuroblasts instead migrating to the site of injury. With the observation of large numbers of neuroblasts at the injury site, we wanted to model the integration potential of SVZ derived neuroblasts without normal development. Using a novel live imaging assay, I found neuroblast maturational state is associated with distinct migratory properties and apical dendrite targeting ability. Microarray analyses of SVZ neuroblasts during migration show significant changes in gene expression profiles from birth to just prior to circuit integration in the OB. Furthermore, I present evidence that newborn SVZ interneurons require Ankyrin3 (Ank3) for precise action potential generation and survival in the OB. After photothrombotic cortical injuries, neuroblasts that migrate to the injury site are unable to upregulate Ank3. </p><p>These research presents a novel insight into the on the cellular identity of the NSC response to injury, and understanding how neuroblast development influences SVZ neuroblasts integration capabilities. New directions from this study include, additional study of Thbs4hi astrocytes' role after injury. Additionally, great progress can be made using the gene expression data to optimize neuroblast integration in health and after injury. Understanding the processes of NSC injury response and neuroblast integration will provide useful insight into nervous system function.</p> / Dissertation

<p> The process by which new learning generates a long-term memory is termed consolidation. Long-term memories are not established instantaneously with learning, but are built through a number of time-dependent processes. Stress and emotional arousal are known to modulate memory consolidation through the action of hormones and neurotransmitters such as noradrenaline. Although most studies done thus far on memory mechanisms have focused on the role of neurons, it is becoming increasingly clear that the glial cells astrocytes play active roles in cognitive processes including learning and memory. Our laboratory has shown that, in rats, the astrocytic breakdown of glycogen into lactate, and lactate transport into neurons, are required in the hippocampus for long-term potentiation (LTP) and for the consolidation of inhibitory avoidance, a type of fear-based contextual memory. These results demonstrated that astrocytic-neuronal metabolic coupling mediated by lactate is an essential mechanism of long-term synaptic plasticity and long-term memory consolidation. My work in this thesis expanded on these findings and asked three questions. First, is lactate-mediated metabolic coupling a general mechanism of plasticity occurring in different brain regions? Second, is there a role for this metabolic coupling in the modulation of memory consolidation mediated by stress? Third, what is the function of lactate transported into neurons? </p><p> Indeed, the coordinated function of multiple brain regions is critical for consolidation. The hippocampus is an essential brain structure for long-term memory formation, with important contributions from the amygdala for modulation of the emotional valence of a memory, and over time, an increasingly important role of cortical structures for memory storage. </p><p> In Chapter I, I demonstrate that breakdown of astrocytic glycogen into lactate also plays a role in long-term memory formation in the basolateral amygdala and anterior cingulate cortex. In Chapter II, I describe how astrocytes mediate the effect of the neuromodulator noradrenaline on memory formation in the hippocampus. Specifically, &beta;₂-adrenergic receptors expressed in astrocytes but not neurons are required for memory consolidation. &beta;₂-adrenergic receptors mediate lactate release from astrocytes and memory impairment due to knockdown of &beta;₂-adrenergic receptors in astrocytes can be rescued by administration of lactate. Thus, these astrocytic adrenergic receptors critically support memory by engaging astrocyte-neuron metabolic coupling via lactate. </p><p> In Chapter III, I show that the function of this lactate is to critically provide energetic support for neuronal changes required for memory consolidation. </p><p> Altogether my results suggest that astrocytic mechanisms play an essential role in memory consolidation in different brain regions and that stress-mediated noradrenergic regulation critically engages astrocytic adrenergic receptors. They also show that these metabolic coupling mechanisms are important because they provide energy for neuronal molecular changes supporting memory formation.</p>

<p>Membrane trafficking in dendritic spines is critical for regulating the number of channels and spine structure during synaptic plasticity. Here I report two small Rab GTPases, Rab4 and Rab10, oppositely regulate AMPA receptors (AMPARs) trafficking and structural plasticity of dendritic spines. Combining two-photon glutamate uncaging with two-photon fluorescence lifetime imaging microscopy (2pFLIM), I found that Rab4 is transiently activated whereas Rab10 is persistently inactivated in the stimulated spines during structural long-term potentiation (sLTP). Inhibition of Rab4 signaling has no effect on GluA1 endocytosis but inhibits activity-dependent GluA1 exocytosis. Conversely, disruption of Rab10 signaling inhibits GluA1 endocytosis while enhancing activity-dependent GluA1 exocytosis. In summary, these results uncover a new mechanism to establish the specificity and directionality of AMPARs trafficking and sLTP via distinct regulations of Rab4 and Rab10 signaling.</p> / Dissertation

<p>How does the visual system determine the direction and speed of moving objects? In the primate brain, visual motion is processed at several stages. Neurons in primary visual cortex (V1), filter incoming signals to extract the motion of oriented edges at a fine spatial scale. V1 neurons send these measurements to the extrastriate visual area MT, where neurons are selective for direction and speed in a manner that is invariant to simple or complex patterns. Previous theoretical work proposed that MT neurons achieve selectivity to pattern motion by combining V1 inputs consistent with a common velocity. Here, we performed two sets of experiments to test this hypothesis. In the first experiment, we recorded single-unit V1 and MT responses to drifting sinusoidal gratings and plaids (two gratings superimposed). These stimuli either had jointly varying direction and drift rate (consistent with a constant velocity) or independently varying direction and drift rate. In the second experiment, we presented arbitrary, randomly chosen combinations of gratings in rapid succession, to sample as widely as possible the space of stimuli that could excite or suppress neural responses. Responses to single gratings alone were insufficient to uniquely identify the organization of MT selectivity. To account for MT responses to both simple and compound stimuli, we developed new versions of an existing cascaded linear-nonlinear model in which each MT neuron pools inputs from V1. We fit these models to our data. By comparing the performance of the different model variants and examining their parameters that best accounted for the data, we showed that MT responses are best described when selectivity is organized along a common velocity. This confirms previous predictions that MT neurons are selective for the arbitrary motion of objects, independent of object shape or texture. We explore new model variants of MT computation that capture this behavior. These studies show that in order to characterize sensory computation, stimuli must be complex enough to engage the nonlinear aspects of neural selectivity. By exploring different linear-nonlinear model architectures, we identified the essential components of MT computation. Together, these provide an effective framework for characterizing changes in selectivity between connected sensory areas. Supplementary materials: figures 3.4(a-e), 3.10(a-e), and 3.14(a-e) are rendered as movies.

<p>The neurotransmitter L-Glutamate is the primary excitatory neurotransmitter of sensory neurons in the dorsal root ganglion (DRG). These neurons may also express ionotropic glutamate receptors, causing the potential for them to be directly excited by their own release of glutamate, from a neighboring neuron, or from other tissues. Glutamate is elevated in tissues after injury or inflammation, and iGluR signaling from the periphery has been shown to increase signaling in DRG neurons and contribute to the development of chronic pain. Targeting pharmacologic intervention of sensory neuron iGluRs present in peripheral terminals may constitute an attractive alternative or augmentation to chronic pain treatment regimens. A compartmented culture system was devised to enable the co-culture of sensory neurons and keratinocyte stem cells in discrete compartments to simulate a skin tissue in vitro, and allow focal agonist application to peripheral terminals. Activation of peripheral receptors with focal agonist application caused the propagation of signals towards somata of neurons in a fluidically separated compartment, causing excitatory post-synaptic currents (EPSC) that were observed and recorded via voltage-clamped whole-cell electrophysiology. EPSC responses observed exhibited statistically significant differences between the ? values of the EPSCs after respective agonist exposure. Immunofluorescent labeling and visualization of receptor expression showed that iGluR subunits are expressed in sensory neuron somata, sensory neuron peripheral processes, non-neuronal cells from the DRG, and keratinocyte stem cells. The implementation of this co-culture clamping facilitates the spatially discrete interaction of neuronal and non-neuronal cell types for the characterization of their interfaces, as well as for the discrete application of pharmacologic agents along axons to evaluate their spatially constrained influence on activity at a cellular, and intercellular level. The spatially restricted application of agonists represents a chemotransmissive instigation of electrochemical activity in neurons for studying EPSCs, instead of electrically stimulating a presynaptic cell, and so more faithfully represents what would occur in vivo. Using this system to test novel pharmaceuticals represents an intermediary step between the study of ligand interactions with receptors and systemic administration to experimental animals. The identification of the active receptors and their subunit-specific peripheral expression yield alternative therapeutic targets for chronic pain treatment.