Browsing by Subject "Hippocampus"
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Item 3 Tesla Magnetic Resonance Imaging of Hippocampal Asymmetry: Results from the Dallas Heart Study(2013-08-01) Lucarelli, Richard T.; Peschock, Ronald M.Keywords: hippocampal asymmetry, hippocampus freesurfer fsl, mesial temporal sclerosis, temporal lobe ipilepsy Background Asymmetry of the hippocampus is regarded as an important clinical finding but limited data on hippocampal asymmetry is available for the general population. Here we present hippocampal asymmetry data from the Dallas Heart Study determined by automated methods and its relationship to age, sex, and ethnicity. Methods 3D-MPRAGE MRI were obtained in 2082 DHS-2 participants. The MR images were analyzed using two standard automated brain segmentation programs, FSL-FIRST and Freesurfer. Individuals with imaging error, self-reported stroke, or major structural abnormalities were excluded. Statistical analyses were performed to determine significance of the findings across age, sex, and ethnicity. Results At the 90th percentile FSL-FIRST demonstrated hippocampal asymmetry of 9.8% (95% CI 9.3 to 10.5%). The 90th percentile of hippocampal asymmetry measured by the difference between hippocampii over the larger hippocampus was 17.9% (95% CI 17.0 to 19.1%). Hippocampal asymmetry increases with age (P=0.0216) and men have greater asymmetry than women as shown by FSL-FIRST (P=0.0036), but ethnicity is not significantly correlated with asymmetry. To confirm these findings Freesurfer was used. Freesurfer showed asymmetry of 4.4% (95% CI 4.3 to 4.7%) normalized to total volume, and 8.5% (95% CI 8.3 to 9.0%) when normalized by difference/larger hippocampus. Freesurfer also showed that hippocampal asymmetry increases with age (P=0.0024), and that men had greater asymmetry than women (P=0.03). Conclusion There is a significant degree of hippocampal asymmetry in the population. The data provided will aid in the research, diagnosis, and treatment of temporal lobe epilepsy and other neurological diseaseItem Adaptive responses of central cholinergic systems in transgenic mice(2006-08) Hartmann, Joachim; Klein, Jochen; Lockridge, Oksana; Löffelholz, Konrad; Mehvar, Reza; Stoll, JamesIn the current thesis, the function of the septohippocampal cholinergic nervous system was investigated in transgenic mouse models pertinent to Alzheimer’s disease. First, a transgenic model of increased amyloid formation and deposition was investigated to see whether a cholinergic deficit, as observed in the human disease, is present in those animals. These mice express both a mutated human amyloid precursor protein and human presenilin-1 and generate amyloid peptide and neuritic plaques in an age-dependent manner. High-affinity choline uptake (HACU) into corticohippocampal synaptosomes showed no difference between double mutant transgenic mice and controls, indicating unchanged turnover of the neurotransmitter, acetylcholine (ACh). Extracellular levels of ACh, measured in the dorsal hippocampus using microdialysis, were not significantly different between groups. The response of these levels to stimulation with either scopolamine or by exposure of animals to a novel environment was also unchanged between mutant mice and controls, indicating retained capability of the central cholinergic system to respond to different challenges. In conclusion, this study demonstrated that amyloid pathology can occur without compromising hippocampal cholinergic neurotransmission. For the second part of this thesis, mice deficient for the enzyme acetylcholinesterase (AChE) were obtained; they serve as a model of the predominant treatment used in Alzheimer’s disease, inhibition of AChE. Microdialysis in dorsal hippocampus revealed vastly elevated baseline levels of ACh, whereas baseline levels of Ch were reduced. Selective inhibition of butyrylcholinesterase (BChE) further increased these levels of ACh in AChE-deficient, but not in control mice. This observation, for the first time, provides clear evidence that BChE can hydrolyze ACh in the brain of a living organism. Elevated levels of ACh were sensitive to the absence of calcium and to tetrodotoxin, confirming their neuronal origin. A compensatory increase in HACU was found, indicating increased transmitter turnover. Furthermore, it was demonstrated that extracellular levels of Ch become rate-limiting for ACh release in the absence of AChE. Finally, a relative failure of presynaptic negative autofeedback receptors was observed. The conclusion is reached that, in the absence of AChE, ACh hydrolysis is maintained to a considerable degree by BChE. Moreover, compensatory changes in the absence of AChE include upregulation of HACU and functional loss of inhibitory autofeedback receptors. In summary, both mouse models demonstrate that central cholinergic systems can respond to a wide range of challenges with a remarkable degree of adaptation.Item Adaptive responses to cellular stress in neurons of the hippocampus(2013-08) Clemens, Ann M.; Johnston, Daniel, 1947-; Harris, Kristen M.Disruptions of endoplasmic reticulum (ER) Ca²⁺ homeostasis are heavily linked to neuronal pathology. Depletion of ER Ca²⁺ stores can result in cellular dysfunction and potentially cell death, although adaptive processes exist to aid in survival. This dissertation examines the age and region-dependence of one postulated adaptive response to ER store depletion, store depletion (SD) HCN channel plasticity, in neurons of the dorsal (DHC) and ventral (VHC) hippocampus from adolescent and adult rats. Using whole-cell patch clamp recordings from the soma and dendrites of CA1 pyramidal neurons, the change in h-sensitive measurements in response to store depletion, induced by treatment with cyclopiazonic acid (CPA), a sarco/endoplasmic reticulum Ca²⁺-ATPase blocker were observed. While DHC and VHC neurons in adolescent animals responded to store depletion with a peri-somatic expression of SD h plasticity, it was found that adult animals express SD h plasticity with a dendritic and somato-dendritic locus of plasticity in DHC and VHC neurons, respectively. Furthermore, SD h plasticity in adults was dependent on membrane voltage and on the activation of L-type voltage gated Ca²⁺ channels. These results suggest that cellular responses to the impairment of ER function, or ER stress, are dependent upon brain region and age, and that the differential expression of SD h plasticity could provide a neural basis for region and age-dependent disease vulnerabilities.Item Akt: it's role in neuronal viability and protection against ischemia in the rat hippocampus(Texas Tech University, 2006-05) Omidvar, Kamran; Fowler, John C.; Roghani, Ali; Strahlendorf, Jean C.According to the American Stroke Association, about 700,000 people suffer a new or recurrent stroke each year in the United States. Of these people, approximately 163,000 die, making stroke the third leading cause of death in the U.S., only behind heart disease and cancer. Depending on the area of the brain affected by the stroke, functions such as motor activity, speech, behavior, and/or memory can be hampered. The hippocampus is a bilateral structure that is highly susceptible to hypoxic and/or ischemic insult. One of the early responses to ischemia is the transient and reversible inhibition of synaptic activity mediated by endogenous adenosine acting on neuronal A1 receptors. Increase in adenosine during ischemia is thought to play a key prosurvival role by attenuating excitotoxic damage through inhibiting glutamate release and activating Akt. Akt is activated by PI3K-dependent and PI3K-independent mechanisms. Akt, also known as PKB, has been shown to be both necessary and sufficient to promote cell survival by growth factors in vitro. Akt directly phosphorylates multiple proteins resulting in the inhibition of apoptotic and/or necrotic cell death. Bcl-2 and Bcl-xL are two proteins that are disinhibited by the direct Akt phosphorylation of Bad. These two proteins function to maintain mitochondrial integrity during ischemia, thus inhibiting the release of cytochrome c which is a strong inducer of the apoptotic pathway. This thesis explores the activation mediated by PI3K and the significance of this activation in neuronal survival mechanisms.Item Akt: It's role in neuronal viability and protection against ischemia in the rat hippocampus(2006-05) Omidvar, Kamran; Fowler, John C.; Roghani, Ali; Strahlendorf, Jean C.According to the American Stroke Association, about 700,000 people suffer a new or recurrent stroke each year in the United States. Of these people, approximately 163,000 die, making stroke the third leading cause of death in the U.S., only behind heart disease and cancer. Depending on the area of the brain affected by the stroke, functions such as motor activity, speech, behavior, and/or memory can be hampered. The hippocampus is a bilateral structure that is highly susceptible to hypoxic and/or ischemic insult. One of the early responses to ischemia is the transient and reversible inhibition of synaptic activity mediated by endogenous adenosine acting on neuronal A1 receptors. Increase in adenosine during ischemia is thought to play a key prosurvival role by attenuating excitotoxic damage through inhibiting glutamate release and activating Akt. Akt is activated by PI3K-dependent and PI3K-independent mechanisms. Akt, also known as PKB, has been shown to be both necessary and sufficient to promote cell survival by growth factors in vitro. Akt directly phosphorylates multiple proteins resulting in the inhibition of apoptotic and/or necrotic cell death. Bcl-2 and Bcl-xL are two proteins that are disinhibited by the direct Akt phosphorylation of Bad. These two proteins function to maintain mitochondrial integrity during ischemia, thus inhibiting the release of cytochrome c which is a strong inducer of the apoptotic pathway. This thesis explores the activation mediated by PI3K and the significance of this activation in neuronal survival mechanisms.Item Astrocytic Contribution to the Glutamatergic Transmission in Schizophrenia(2011-02-01T19:33:32Z) Stan, Ana Despina; Tamminga, CarolSchizophrenia is a chronic mental disorder encompassing an array of cognitive and behavioral manifestations. Although the disease molecular pathophysiology remains essentially unknown, evidence exists for abnormalities within all the main neurotransmitter systems and various cortical and subcortical brain structures, albeit with no unifying/overarching hypothesis connecting the existent knowledge. Moreover, no current animal model or biological construct reproduces the complexity of the disease with acceptable validity. In my work I have taken a multidisciplinary approach to study the live and postmortem human brains of people with schizophrenia, focusing specifically on the glutamatergic abnormalities in the hippocampus, one brain region repeatedly found to bear structural, molecular, and blood flow abnormalities in the disease. I have started with the in vivo measurement of glutamate and glutamine using magnetic resonance spectroscopy, thus getting a “high-level” sense of the glutamatergic transmission changes in the hippocampi of subjects with schizophrenia. Concretely, I have found that untreated people with schizophrenia have reduced levels of glutamate compared to their healthy counterparts, but this reduction can be partially reversed by antipsychotic medication. To allow for a more “small-scale” characterization of the glutamatergic transmission impairments, I have used postmortem brain tissue to zoom in on the glutamatergic synapse, viewed as a “tripartite synapse”. Apart from the pre- and postsynaptic neurons, the third component is represented by the astrocyte, the brain glial cell that is responsible for most of the glutamate recycling and that attunes the glutamatergic synapse to the overall energetic metabolism of the brain. I have found that glutamate recycling is impaired in schizophrenia, selectively in the dentate gyrus, one of vii the hippocampal subregions, and the specific abnormalities reside in the glutamate transporters, responsible clearing up synaptic glutamate.Item Coordinated structural plasticity across synapses in the adult hippocampus(2015-05) Chirillo, Michael August; Harris, Kristen M.; Bear, Mark F; Colgin, Laura L; Golding, Nace L; Raab-Graham, Kimberly FNeural circuitry is determined primarily by trillions of synaptic junctions that link cells in the nervous system. Understanding how the structure of the synapse influences its function has been a central goal of cellular neuroscience since synapses were first recognized more than a century ago. Long-term potentiation (LTP), a long lasting enhancement of synaptic efficacy, is a well-characterized cellular correlate of learning and memory that results in dramatic structural remodeling of the synapse. Research has focused heavily on the postsynaptic structural remodeling that occurs to support LTP, but concomitant presynaptic and subcellular remodeling during LTP has been left largely unexplored. To address these questions, three-dimensional reconstructions from serial section electron microscopy of presynaptic boutons, vesicle pools, and dendritic smooth endoplasmic reticulum (SER) in hippocampal area CA1 were created and quantified. The data presented in this dissertation demonstrate that coordinated structural plasticity occurs at both pre- and postsynaptic sides of adult hippocampal synapses by 2 hours during LTP induced with theta burst stimulation. Presynaptically, the number of presynaptic boutons correlated perfectly with fewer dendritic spines during LTP that were previously reported, suggesting that synaptic units act as cohesive structures. Vesicle pools were mobilized and vesicle transport packets were moved into boutons or were released in transit. Dendritic SER is a ubiquitous intracellular membranous network involved in calcium signaling and protein modification. The complexity of SER influences the movement of diffusible membrane cargo. SER was dramatically remodeled during LTP, redistributing from the shaft of the dendrite into spines and becoming highly complex near synapses that were largest during LTP. As a preliminary investigation into how normal mechanisms of structural plasticity described in this dissertation might go awry under conditions of synaptic pathology, three-dimensional reconstructions of CA1 synaptic ultrastructure in a mouse model of Fragile X, which is known to express exaggerated mGluR-dependent long-term depression (LTD), were created and quantified. Synaptic ultrastructure was similar with that of the wild-type mouse, suggesting that structural malformation in FX might be confined to development or to other brain regions.Item Grid cell attractor networks: development and implications(2015-12) Widloski, John Eric; Fiete, Ila; Marder, Michael P., 1960-; Gordon, Vernita; Pillow, Jonathan; Swinney, HarryAt the foundation of our ability to plan trajectories in complex terrain is a basic need to establish one’s positional bearings in the environment, i.e., to self-localize. How does the brain perform self-localization? How does a net- work of neurons conspire to solve this task? How does it self organize? Given that there might be multiple solutions to this problem, with what certainty can we say that any such model faithfully captures the neural structure and dynamics as it exists in the brain? This thesis presents a collection of three theoretical works aimed at addressing these problems, with a particular focus on biological plausibility and amenability to testing experimentally. I first introduce the context within which the work in the thesis is situ- ated. Chapter 1 provides a framework for understanding algorithmically how the brain might solve the problem of self-localization and how a neural circuit could be organized to perform self-localization based on the integration of self-motion cues, an operation known as path integration. We also introduce the neurobiology that underlies self-localization, with special emphasis on the cell types found in and around the hippocampus. We discuss the case that a particular class of cells – grid cells – subserve path integration, because of their peculiar spatial response properties and their anatomical positioning as the recipients of self-motion information. Continuous attractor models are introduced as the favored description of the grid cell circuit. Key open questions are introduced as motivation for the subsequently described work. I next focus on the question of how the grid cell circuit may have organized. In Chapter 2, it is demonstrated that an unstructured immature neural network, when subjected to biologically plausible inputs and learning rules, can learn to produce grid-like spatial responses and perform path integration. This model makes a number of predictions for experiment which are described at length. In Chapter 3, I describe a theoretically motivated experimental probe of the organization and dynamics of the grid cell circuit. The proposed experiment relies on sparse neural recordings of grid cells together with global perturbations of the circuit (and is thus experimentally feasible). It promises to yield special insight into the hidden structure of the grid cell circuit. Finally, in Chapter 4, I provide an analytical treatment of pattern formation dynamics in the grid cell circuit. This work focuses on nonlinear effects.Item The Impact of Opioids and Opiates on Adult Hippocampal Neurogenesis(2007-12-17) Harburg, Gwyndolen Colleen; Eisch, Amelia J.Opiate addiction is a growing problem in today's society. Thus, it is of crucial importance that we understand the physiological basis for opiate addiction and the long-term consequences of opiate use in order to develop more effective means of treatment. Chronic morphine and heroin have previously been shown to decrease proliferation and survival of progenitor cells in the adult rat and mouse hippocampus. Here, I show that endogenous opioids may act through the mu opioid receptor (MOR) to similarly decrease survival of new hippocampal neurons. An exon 1 MOR knockout mouse showed increased survival of new neurons independent of effects on cell proliferation or cell death. In concordance with the increased numbers of granule cells maturing into neurons, knockout mice also had larger hippocampal granule cells layers and increased numbers of granule cells. Exploration of the impact of chronic morphine on different stages of neurogenesis showed that chronic morphine decreased numbers of Type 1 stem cells and proliferating progenitor cells. Progenitor cells exposed to chronic morphine during early maturation were not significantly decreased in number, but appeared to have retarded cell maturation since fewer had reached the immature neuron stage in chronic morphine mice. Chronic morphine also appeared to result in anterior hippocampus specific decreases in stem cells as well as maturation retardation. These findings show that morphine has distinct effects on different stages of neurogenesis, and that the anterior hippocampus may be more sensitive to some effects. Cell proliferation levels in the brains of human heroin abusers and normal controls were assessed using the endogenous proliferation marker Ki67. Heroin abusers had decreased numbers, but larger clusters of proliferating cells in the dentate gyrus hilus as compared with controls. There was also a trend towards a decrease in number of proliferating cells in the granule cell layer of heroin abusers. Although these findings are preliminary, they suggest that chronic heroin use in humans, as in rodents, may negatively impact neurogenesis. Together, these findings support a negative role for opioids and opiates in regulating adult hippocampal neurogenesis.Item Investigation of firing properties in CA1 hippocampal pyramidal neurons in a mouse model of Fragile X syndrome(2012-12) Dickson, Andrea Haessly; Johnston, Daniel, 1947-; Aldrich, Richard W; Harris, Kristen MFragile X Syndrome is the most common form of heritable cognitive disability. It is caused by a genetic mutation that leads to a lack of protein from the FMR1 gene. This protein (FMRP) is used to regulate the translation of many other proteins, thereby leading to a wide range of effects. Because the origin of this disease is based on the lack of a single protein, an animal model with construct validity can be used to investigate the potential effects leading to the symptoms of the disease. Many studies have investigated the synaptic plasticity differences of CA1 pyramidal neurons between a mouse model of fragile X syndrome (KO) and a wild type mouse (WT). This study investigates the differences in firing properties of a CA1 pyramidal neuron between the KO and WT. Specifically, contributions of two ion channels are investigated: the Ca2+ and voltage activated potassium channel (BK) and the potassium channel (M) inhibited by the muscarinic acetylcholine receptor. This study finds some differences that warrant further investigation, including differences in spike timing, spike width and the initial rate of rise of an action potential. However, several areas of investigation yield subtle or confounding results, which may indicate that the CA1 pyramidal neurons affected by the lack of FMRP may make up more than one population.Item Knockdown of HCN1 channels in the dorsal hippocampal CA1 region(2011-12) Kim, Chung Sub; Johnston, Daniel, 1947-; Aldrich, Richard; Mauk, Michael; Raab-Graham, Kimberly; Seidemann, EyalThe hippocampus is an integral brain region for affective disorders. HCN1 protein shows age-dependent increase in expression resulting in an increase in I[subscript h] in the dorsal hippocampal CA1 region. TRIP8b knockout mice lacking functional HCN channels as well as both HCN1 and HCN2 knockout mice have been shown to display antidepressant-like behaviors. The mechanisms or brain regions involved in these alterations in behavior, however, are not clear. We developed a lentiviral shRNA system to examine whether knockdown of HCN1 protein, and therefore h-channels, in the dorsal hippocampal CA1 region is sufficient to produce antidepressant-like effects. We found that silencing of HCN1 gene resulted in physiological changes consistent with a reduction of I[subscript h] and increased cellular excitability of CA1 pyramidal neurons. Rats infused with lentiviral-shRNA-HCN1 in the dorsal hippocampal CA1 region displayed antidepressant- and anxiolytic-like behaviors. Using voltage-sensitive dye imaging, we found that knockdown of HCN1 in the dorsal hippocampal CA1 region led to enhancement of hippocampal activity in large regions of the dorsal hippocampus. Our results demonstrate that changed hippocampal network activity by local manipulation of HCN1 channels in dorsal hippocampus led to anxiolytic- and antidepressant-like behaviors and suggest that HCN1 channels could be a potential target for treatment of anxiety and depression.Item Optimization of the Fair Technique for Specific Brain region Perfusion Studies(2009-01-14) Li, Xiufeng; Briggs, Richard W.Most of the technical development and applications of ASL (arterial spin labeling) imaging have mainly focused on the superior cortical regions of the brain. However, optimal ASL measurements to quantify cerebral blood flow (CBF) in specific brain regions may require optimized parameters, improved techniques, or new imaging schemes based upon physiological or anatomic characteristics of those brain regions. In this thesis, the advantages of this region-targeted approach are demonstrated by performing quantitative perfusion studies of two representative brain regions, the cerebellum in the inferior part of the brain and the hippocampus in the mid-brain. To minimize or eliminate the venous artifacts found in cerebellum perfusion studies using traditional FAIR (flow-sensitive alternating inversion recovery) technique, FAIR ASST (FAIR with active suppression of superior tagging technique), as well as MDS FAIR, (modulated dual saturation pulse trains for FAIR) was developed and compared to PICORE (proximal inversion with a control for off-resonance effects) for quantifying cerebellum perfusion. The data indicate that FAIR ASST yields more robust CBF (cerebral blood flow) measurements. OPTIMAL FAIR (orthogonally-positioned tagging imaging method for arterial labeling of FAIR) was developed and shown to reduce the heterogeneity of within-slice transit time and to minimize partial volume effects, improving quantitative CBF maps for cerebellum and hippocampus. These techniques were optimized and applied to the study of perfusion abnormalities in brain regions important to the study of Gulf War Syndrome. Together with regionally optimized parameters, these ASL methods provide more reliable, efficient, accurate, and artifact-free CBF measurements than methods previously available.Item Persistent and transient Na⁺ currents in hippocampal CA1 pyramidal neurons(2011-08) Park, Yul Young; Johnston, Daniel, 1947-; Bajaj, Chandrajit L.; Ben-Yakar, Adela; Dunn, Andrew; Shouval, HarelThe biophysical properties and distribution of voltage gated ion channels shape the spatio-temporal pattern of synaptic inputs and determine the input-output properties of the neuron. Of the various voltage-gated ion channels, persistent Na⁺ current (INaP) is of interest because of its activation near rest, slow inactivation kinetics, and consequent effects on excitability. Overshadowed by transient Na⁺ current (INaT) of large amplitude and fast inactivation, various quantitative characterizations of INaP have yet to provide a clear understanding of their role in neuronal excitability. We addressed this question using quantitative electrophysiology to compare somatic INaP and INaT in 4–7 week old Sprague-Dawley rat hippocampal CA1 pyramidal neurons. INaP was evoked with 0.4 mV/ms ramp voltage commands and INaT with step commands in hippocampal neurons from in vitro brain slices utilizing nucleated patch-clamp recording. INaP was found to have a density of 1.4 ± 0.7 pA/pF in the soma. Compared to INaT, it has a much smaller amplitude (2.38% of INaT) and distinct voltage dependence of activation (16.7 mV lower half maximal activation voltage and 41.3% smaller slope factor than those of INaT). The quantitative measurement of INaT gave the activation time constant ([tau]m) of 22.2 ± 2.3 [mu]s at 40 mV. Hexanol, which has anesthetic effects, was shown to preferentially block INaP compared to INaT with a significant voltage threshold elevation (4.6 ± 0.7 mV) and delayed 1st spike latency (221 ± 54.6 ms) suggesting reduced neuronal excitability. The number of spikes evoked by either given step current injections or [alpha]-EPSP integration was also significantly decreased. The differential blocking of INaP by halothane, a popularly used volatile anesthetic, further supports the critical role of INaP in setting voltage threshold. Taken together, the presence of INaP in the soma demonstrates an intrinsic mechanism utilized by hippocampal CA1 pyramidal neurons to regulate axonal spike initiation through different biophysical properties of the Na⁺ channel. Furthermore, INaP becomes an interesting target of intrinsic plasticity because of its profound effect on the input-output function of the neuron.Item Regulation of Adult Hippocampal Neurogenesis: Insights from Mouse Models of Dementia and Depression(2009-05-13) Donovan, Michael Harry; Eisch, Amelia J.While neurogenesis is largely complete by birth, the subgranular zone (SGZ) in the adult hippocampus continues to produce functional young neurons. The last decade has produced a multitude of research demonstrating that the process of SGZ neurogenesis is dynamically regulated. Stimuli that negatively impact SGZ neurogenesis include stress, depression models, aging and models of neurodegenerative disease. Positive regulators of SGZ neurogenesis include antidepressants and hippocampal-dependent learning. These results have sparked tremendous speculation, both scientific and popular, that adult hippocampal neurogenesis might be critical for mood regulation and/or memory, and might be a promising target for the treatment of depression and dementia. However, we still know little about underlying mechanisms of how increases and decreases in SGZ neurogenesis occur. Here, I examine several manipulations of adult hippocampal neurogenesis, focusing on potential neuromechanisms underlying alterations in SGZ neurogenesis. First, in a mouse model of dementia, I find that in addition to agedependant decline in SGZ proliferation, these mice have retarded migration and maturation of new SGZ neurons and ectopic proliferation in a normally non-neurogenic region. Second, I explore how the antidepressant fluoxetine increases SGZ neurogenesis. I show that the increase occurs only after chronic administration and is not preceded by changes in cell death, cell-cycle or proliferating cell lineage. I next address the capacity of proliferating SGZ cells to respond to brain-derived neurotrophic factor (BDNF), a neurochemical implicated in antidepressant action and neurogenesis regulation. I find that most proliferating cells do not contain the necessary TrkB receptors in vivo, and thus BDNF action is likely indirect or through type-1 stem cells, which contain TrkB. Finally, I look at changes in neurogenesis in a social-defeat depression model. I find that, like other models of repeated stress, social-defeat stress appears to produce a stress-induced decrease in S-phase cells. However, closer analysis reveals that this decrease does not indicate decreased proliferation, and mice that are behaviorally sensitive to the stress actually show an increase in neurogenesis overall. Taken together, these results emphasize the complexity of the processes that comprise adult hippocampal neurogenesis, highlighting the importance of further investigation into the neuromechanisms of changes in neurogenesis.Item Regulation of Synaptic Vesicle Trafficking at Central Synapses(2009-09-04) Chung, Chihye; Kavalali, Ege T.Synapses are where electrical information is converted to chemical signaling, allowing for careful regulation of inter-neuronal communication in the brain. At presynaptic terminals, synaptic vesicles fuse with plasma membrane in response to electrical stimulation, followed by rapid retrieval to the terminal and re-organization for reuse. Thus, synaptic vesicle trafficking is of interest as to where presynaptic regulations of synaptic transmission begins to occur. The first two chapters explored a novel secretagogue, lanthanum (La3+), and its potential usage as a probe to study vesicle recycling at central synapses. Chapter two describes the characteristics of La3+ -evoked transmission at hippocampal synapses. La3+ has two separate actions on transmission, with a different time course and underlying mechanism of action. This newly characterized rapid action of La3+ is intracellular Ca2+ -independent, in contrast to its delayed action, yet requires functional SNARE complex formation. Therefore, chapter three took advantage of La3+-evoked transmission as a tool to investigate the coupling between exo- and endocytosis in SNARE-dependent fusion. Using multifaceted approaches, I propose that La3+ induces transmitter release via narrow fusion pore opening and closure, or a 'kiss-and-run' mode of exo- and endocytosis. Chapter four investigates the molecular requirement for the synaptic vesicle recycling pathway. I analyzed the impact of one of main players in endocytosis, dynamin in different forms of release. Acute inhibition of dynamin in central synapses impairs activity-dependent synaptic vesicle recycling while leaves spontaneous recycling intact, suggesting the operation of two parallel recycling pathways in central synapses as well as proposing the molecular signature between spontaneously and activity-dependently recycling pathways. In chapter five, I further investigated the origins of spontaneously recycling synaptic vesicles by simultaneous monitoring of spectrally separable FM dyes, as chapter suggested four that they are originated from an isolated pool. This chapter includes comprehensive analysis of the endocytic pathway operating at rest and its molecular participants -specifically dynamin, which was implicated to play a role in the endocytic pathway from observations I made in chapter four. Chapter six expands the investigation as to how presynaptic signaling regulates synaptic vesicle trafficking in glutamatergic synapses. I focused on the impact of ambient glutamate concentration on vesicle recycling as a feedback signal to rapid synaptic reuse to impact short-term synaptic plasticity. Taken together, these results suggest that synaptic vesicle trafficking is an actively regulated process, impacting various aspects of information cascades between neurons.Item The Role of Adult Neurogenesis in Cocaine Addiction(2009-01-14) Noonan, Michele Ann; Eisch, AmeliaNew neurons are born in the adult hippocampus in a region known as the subgranular zone (SGZ). This process is dynamically regulated and new neurons are thought to be important for certain types of spatial learning and memory. Proliferation of SGZ neural progenitors is decreased by drugs of abuse, yet it is not clear how the type and amount of drug as well as the pattern of administration changes long-term effects on neurogenesis. In addition, it is unclear what role if any SGZ neurogenesis plays in initiating drug-taking or relapse behaviors, or whether changes in neurogenesis are merely side effects of drug-taking. I first examined effects of chronic cocaine self-administration and withdrawal on the different stages of neurogenesis. I found an early deficit in proliferation of neural progenitors, as well as a 4 week delayed increase in doublecortin-positive (DCX+) immature neurons which were common to both rats in withdrawal or those continuing to self-administer cocaine. I next asked the question of the functional consequence of changes in adult hippocampal neurogenesis to the acquisition and maintenance of drug-taking, as well as relapse to drug-taking. I found that reduced adult neurogenesis via cranial irradiation prior to cocaine-taking was associated with increased acquisition of drug-taking and increased motivation for cocaine, but not sucrose, while reduced adult neurogenesis after rats have acquired cocaine self-administration was associated with increased resistance to extinction of drug-seeking behavior. Finally, I asked if formation of drug-context associations would be altered in rodents with reduced neurogenesis in a passive drug exposure paradigm. I found that a transgenic mouse with reduced adult neurogenesis has impaired long-term drug-context memory in the cocaine conditioned place preference paradigm (CPP). Together these findings suggest that reduced adult hippocampal neurogenesis is a risk factor for drug addiction, that decreased proliferation after chronic drug intake likely contributes to drug-taking and drug-seeking behaviors, and that the delayed increase in immature neurons after drug-taking is likely protective against relapse. In sum, increases in adult hippocampal neurogenesis are beneficial both to the naïve and addicted brain, and therapeutics specifically increasing adult neurogenesis could aid in preventing initial addiction as well preventing future relapse.Item The Role of Chromatin Remodeling in Hippocampus in Depression and Antidepressant Action(2008-05-13) Tsankova, Nadeja Mincheva; Nestler, Eric J.This thesis presents a novel level by which neuroplastic changes in the brain may be disrupted with depression and reversed by treatment with antidepressants: regulation at the level of chromatin remodeling. The technique of brain chromatin immunoprecipitation was pioneered to directly measure the in vivo modifications of histones, a form of chromatin remodeling, at gene promoter regions in the hippocampus after chronic defeat stress, a model of depression, and chronic treatment with the antidepressants imipramine and electroconvulsive seizure (ECS). Chromatin modifications and transcriptional changes were assayed in one gene in particular, the brain-derived neurotrophic factor (BDNF). BDNF is alternatively spliced to generate several mRNA transcripts, driven by unique promoters. I measured the expression levels of each BDNF transcript (I-IV) in rat after ECS, as well as each BDNF transcript (I-V) in mice after chronic stress and imipramine treatments, and found that these chronic treatments induce lasting changes in the expression of specific BDNF splice variants. These changes correlated with sustained modifications in histones at the exact promoter regions, driving the differential changes in BDNF expression. Chronic defeat stress induced robust enrichment of H3-K27 methylation at BDNF P3 and P4 promoters (modifications expected to repress promoter activity), while chronic imipramine in defeated animals lead to lasting upregulation in the levels of H3 acetylation and H3-K4 methylation at P3 and P4 (modifications expected to stimulate promoter activity). Finally, I discovered a novel role for the histone deacetylase HDAC5 in the therapeutic efficacy of chronic imipramine after defeat stress. I found that chronic imipramine downregulates HDAC5 after stress, that HDAC5 overexpression in the hippocampus blocks the behavioral effects of imipramine in defeated mice, that HDAC5 inhibition exerts a subtle antidepressant-like effect, and that HDAC5 deficiency reduces the pathological response to stress. This unexpected role for HDAC5 provides an important mechanistic link between the adaptive chromatin remodeling changes at genes and the ability of chronic antidepressants to exert therapeutic efficacy after chronic stress. These experiments provide one of the first endeavors to understand the role of chromatin remodeling in modulating long-term adaptive changes in brain associated with complex psychiatric conditions, such as depression.Item The Role of Notch1 in adult Hippocampal Neurogenesis and function(2009-09-04) Ables, Jessica Lynn; Eisch, AmeliaNeurogenesis occurs throughout life in the hippocampal subgranular zone (SGZ) and is potently stimulated by exercise, but the underlying mechanisms are still poorly defined. Notch1 is a master regulator of developmental neurogenesis, yet its role in adult hippocampal neurogenesis is unclear. To test the hypothesis that cell-intrinsic Notch1 is critical to both basal and exercise-induced SGZ neurogenesis, we generated Nestin-creERT2/R26R-YFP/Notch1loxP/loxP (Notch1 iKO) mice to inducibly ablate Notch1 in Nestin-expressing stem and progenitor SGZ cells. The total number of YFP+ SGZ cells increased over time in wild type littermates, but not in Notch1 iKO mice. Morphological and phenotypic analyses revealed that fewer YFP+ DG neurons were generated over time in Notch1 iKO mice due to smaller pools of YFP+ stem-like and progenitor cells. Likewise, neural progenitors isolated from Notch1 iKO mice were incapable of forming new neurospheres with extended passaging. While non-running Notch1 iKO mice had fewer YFP+ SGZ cells relative to wild type littermates, Notch1 iKO mice given 30 days access to a running wheel had equal number of YFP+ SGZ cells relative to controls, suggesting that running rescued total YFP+ SGZ cell number independent of Notch1. However, running did not rescue YFP+ stem-like cell number in Notch1 iKO mice, suggesting that the putative stem-like SGZ cells make little contribution to adult hippocampal neurogenesis in these conditions. From these data, we conclude that Notch1 in Nestin+ stem and progenitor cells is critical to maintain basal adult hippocampal neurogenesis, but is not critical for exercise-induced neurogenesis. Neurogenesis has also been implicating in depression and behavioral response to antidepressants. To determine if reduced neurogenesis contributed to depression- or anxiety-related behavior, we assessed several measures of depression and anxiety in Notch1 iKO mice. We found that Notch1 iKO mice did not differ from WT mice in their behavior, suggesting that reduced neurogenesis is not associated with mood disturbances.Item Slow and fast gamma rhythms represent distinct memory processing states in the hippocampus(2015-05) Bieri, Kevin Wood; Colgin, Laura; Preston, Alison; Morikawa, Hitoshi; Drew, Michael; Golding, NaceThe hippocampus is central to learning and memory and participates in both the encoding of new memories and their retrieval. It is not known, however, how these dual functions are processed within the same structure without causing interference between what is actively experienced and what is remembered. Different frequencies of gamma oscillations selectively route inputs to area CA1 of the hippocampus, suggesting that gamma subtypes play a role in differentiating between streams of incoming information. Slow gamma oscillations (~25–55 Hz) couple CA1 to area CA3, a region that is thought to store neuronal representations of past events and is thus important for memory retrieval. Fast gamma oscillations (~60–100 Hz) couple CA1 to MEC, a region that supplies the hippocampus with information about ongoing experiences. In this dissertation, I use hippocampal recordings in freely behaving rats to provide evidence that such slow and fast gamma coupling supports distinct memory retrieval and encoding modes in the hippocampus. This is first examined in the principal neurons of the hippocampus, called ‘place cells’, which are thought to provide the ‘where’ component of episodic memory. It was found that place cells alternated between distinct spatial coding modes, representing upcoming locations during slow gamma and recent locations during fast gamma. This concept was explored further in ‘place cell sequences’, which represent trajectories through space, and are thought to store sequential events of an experience. Sequences coded paths sweeping ahead of the animal during slow gamma, and coded ongoing, real-time locations during fast gamma. Also, it was found that different phases of the slow gamma cycle coded specific locations, suggesting a mechanism for how slow gamma promotes retrieval of multi-item memories. Lastly, slow and fast gamma were examined during novel and familiar experiences. Fast gamma was enhanced during encoding of novel object-place associations, while slow gamma coupling between CA3 and CA1 was associated with retrieval of familiar object-place associations. Taken together, these results support the hypothesis that distinct gamma subtypes provide a novel mechanism for separating the dual “reading” and “writing” functions of the hippocampus.Item Study of the Mechanisms Underlying Hippocampal Neuron Synaptogenesis: The Roles of Neurotrophin Signaling and Micrornas(2010-11-02T18:20:38Z) Zhang, Wei; Parada, LuisSynapse formation requires contacts between dendrites and axons. Although this process is often viewed as axon mediated, dendritic filopodia may be actively involved in mediating synaptogenic contacts. Brain-derived neurotrophic factor (BDNF) increases the density of dendritic filopodia and the conditional deletion of tyrosine receptor kinase B (TrkB) reduces synapse density in vivo (Luikart et al., 2005). Here, we report that TrkB associates with dendritic growth cones and filopodia, mediates filopodial motility, and does so via the phosphoinositide 3 kinase (PI3K) pathway. We used genetic and pharmacological manipulations of mouse hippocampal neurons to assess signaling downstream of TrkB. Conditional knock-out of two downstream negative regulators of TrkB signaling, Pten (phosphatase with tensin homolog) and Nf1 (neurofibromatosis type 1), enhanced filopodial motility. This effect was PI3K-dependent and correlated with synapse density. Phosphatidylinositol 3,4,5- trisphosphate (PIP3) was preferentially localized in filopodia and this distribution was enhanced by BDNF application. Thus, intracellular control of filopodial dynamics converged on PI3K activation and PIP3 accumulation, a cellular paradigm conserved for chemotaxis in other cell types. Our results suggest that filopodial movement is not random, but responsive to synaptic guidance cues. In order to further elucidate the mechanisms of BDNF-TrkB-PI3K pathway downstream signaling involved in regulating dendritic filopodial motility, we used a pharmacological approach as well as a gene expression approach to show that Rac1 and RhoA may play a role in this pathway. Rac1 positively regulated dendritic filopodial motility while RhoA had a negative effect. Our data suggest that BDNF-TrkB signaling might function to regulate the balance between Rac1 and RhoA, thus controlling dendritic filopodial motility. The developing nervous system is shaped by highly orchestrated programs of gene expression. This tight regulation is regulated by various transcriptional and post-transcriptional events that control individual gene expression. The recent discovery of small, non-coding RNAs has greatly expanded our understanding of the mechanisms that regulate gene expression at the post-transcriptional level. Here, I characterized the expression pattern of one neuronal microRNA, miR-381, and used in vitro cultured hippocampal neurons to show that miR-381 regulates neurite growth, as overexpression of miR-381 promotes neuronal dendritic branching. The effect of miR-381 on neuronal dendritic branching might be through a net regulation of multiple target genes.