The mammalian brain is a complex organ, the result of a very specific and regulated differentiation process. Although there are many different cell types in the mammalian brain, neurons make up the bulk of the tissue. Neurons come from the divisions of radial glial progenitors (RGPs), which are columnar stem cells in the developing brain. These cells undergo two types of division: symmetric or asymmetric. Symmetric divisions expand the stem cell population, resulting in two new RGPs. Symmetric divisions are critical for ensuring the stem cell population is not depleted too quickly in development. Asymmetric divisions are neurogenic, producing one RGP and one cell that will either differentiate into one neuron, or an intermediate progenitor (IP) that will divide again and produce two to four neurons (Shitamukai, Konno, and Matsuzaki 2011). Several factors have been linked to this determination, including mitotic spindle orientation, centrosomal inheritance, and exposure to proliferative factors, like sonic hedgehog and Notch (Chenn and McConnell 1995; Gaiano and Fishell 2002; Han 2016). This work will focus on spindle orientation, which has been linked to cell fate in many contexts (Lancaster and Knoblich 2012; Williams and Fuchs 2013; Chenn and McConnell 1995). Spindle orientationmust be tightly controlled in order to expand the RGP cell population in early development, then, with more randomized spindles, to shift to producing neural precursors during cortical expansion (Götz and Huttner 2005). While the exact mechanism is still unknown, the orientation of the mitotic spindle relative to the ventricular surface at the time of division affects what type of division occurs (Lancaster and Knoblich 2012). A related process in RGP neural production is interkinetic nuclear migration (INM), in which the RGP nucleus travels apically and basally in a cell-cycle dependent manner (Noctor et al. 2001; Sauer 1935; Hu et al. 2013). The RGP only divides when the nucleus reaches the apical surface; why this occurs is still not known. INM ensures that only a small population of RGPs is dividing in a controlled manner, allowing for cells to interpret polarity cues and orientthe spindle while dividing. One protein that is important to multiple processes in neuronal development is Kif1A. Kif1A is a kinesin motor that has been shown to be critical for INM, in particular for transporting the nucleus basally after division. When Kif1A expression is reduced using shRNA, RGPs fail to migrate away from the ventricular surface, but continue to go through the cell cycle at a normal rate (Carabalona, Hu, and Vallee 2016). Additionally, RGPs that lack Kif1A also exhibit more horizontal and symmetric divisions. This indicates that Kif1a is involved in asymmetric, oblique divisions that produce neurons. Thus, without Kif1a, RGPs produce fewer neurons, instead expanding the RGP cell population. Another kinesin that may be involved in spindle orientation is Kif13B. Kif13B is in the same kinesin-3 subfamily as Kif1A. While structurally very similar to Kif1A, it does have distinct features. It contains a CAP-gly domain, used for binding to the plus end of microtubules. This domain is absent from other kinesin-3 family members, including the most closely related,Kif13A. Kif13B has been shown to be critical for spindle orientation in polarized Drosophila S2 cells, as well as in neuroblasts (Carabalona, Hu, and Vallee 2016; Siegrist and Doe 2005). Kif13B functions to anchor the mitotic spindle to other factors at the cell cortex during mitosis. This occurs through direct interaction with Discs large (Dlg1), which then connects to other factors at the cell membrane, including G?i, LGN, and NuMA. This is a critical process to ensure daughter cells are properly specified. Many of these factors, including LGN and NuMA have been identified as important spindle regulators in RGP divisions as well. Kif13B binds to Dlg1 and to 14-3-3 ?, which is bound to 14-3-3 ?, bound to NudE and Dynein, connecting the Kif13B to Dynein (Lu and Prehoda 2013). Kif13B, as a kinesin, moves along microtubules towards the plus end. Dynein moves in the opposite direction, towards the minus end. The connection of two opposing motors moving in opposite directions may serve to put tension on the spindle and prevent it from freely moving within the cell. When Kif13B is knocked down or removed in cells, the spindle orients randomly in the cell, not in line with LGN or NuMA at the cell cortex (Siegrist and Doe 2005; Lu and Prehoda 2013). This indicates that in mammalian systems, it likely is important for maintaining orientation, and its loss in RGPs would result in random orientation as well. This would result in more neurogenic divisions in RGPs, which is the opposite of the effect seen with Kif1a shRNA. By using in utero electroporation of embryonic rat brains as well as a mouse model ofKif13b knockout in RGPs, I have shown that Kif13B and Kif1A have opposing roles in neurogenesis. This difference can be traced to an alteration of IP production, which Kif1A shRNA decreases, and Kif13b shRNA increases. This can be further traced to the opposing effects on spindle orientation of dividing RGPs. Kif1a shRNA results in more horizontal spindle angles while Kif13b shRNA or deletion results in more random spindle angles. While the kinesin-3 family members are very similar in structure, there are key differences between them. Kif1A has a cargo binding domain at its C terminus, the pleckstrin homology (PH) domain. Kif13B contains a CAP-gly domain. This difference in tail domains would presumably allow Kif13B to bind to microtubule plus ends, while Kif1A would dissociate from the spindle. This difference, therefore, could explain why these two very similar kinesins appear to be performing the opposite roles in spindle orientation. This work provides evidence for a novel mechanism of regulation of neuron production in the mammalian cortex.

Recent advances in neuroimaging and electromagnetic measurement technology have permitted the exploration of structural and functional brain alterations associated with chronic pain. A number of cortical and subcortical brain regions have been found to be involved in the experience of chronic pain (Baliki et al., 2008; Jensen et al., 2010). Evidence suggests that living with chronic pain shapes the brain from both an architectural and a functional perspective, and that individuals living with chronic pain display altered brainwave activity even at rest. Quantitative EEG (qEEG) is a method of spectral analysis that utilizes a fast Fourier transform algorithm to convert analog EEG signals into digital signals, allowing for precise quantification and analysis of signals both at single electrode locations and across the scalp as a whole. An important advance that has been permitted by qEEG analysis is the development of lifespan normative databases against which individual qEEGs can be compared (Kaiser, 2006; Thatcher et al, 2000). Pilot data utilizing qEEG to examine brainwave patterns of individuals with chronic pain have revealed altered EEG activity at rest compared to age- and gender-matched healthy individuals (Burroughs, 2011). The current investigation extended the findings of the pilot study by utilizing qEEG to examine a larger sample of individuals with chronic pain. Individuals with chronic pain displayed significantly reduced slow wave activity in frontal, central, and temporal regions. Findings will be presented in terms of specific patterns of altered EEG activity seen in individuals with chronic pain.

No description available.

The goal of this experiment was to examine the pattern of ACh release in mPFC and HPC during performance in trace and delay appetitive conditioning.

published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy

Experimentally naive rats exhibit varying degrees of novelty exploration. Some rats display high rates of locomotor reactivity to novelty (high responders; HR), and others display low rates (low responders; LR). The novelty-seeking phenotype (LRHR) is introduced as a model of stress responsiveness. In this thesis I examined effects of chronic variable physical and social stress or control handling on the levels of various neurotrophins in the hippocampus, and changes in mossy fibre terminal fields in LRHR rats. A positive correlation is seen between histone deacetylase 2 and brain-derived neurotrophic factor (BDNF) levels both of which are oppositely regulated in LRHR CA3 fields in response to chronic social stress. Increase in BDNF levels in CA3 field accompanied increase in supra-pyramidal mossy fibre terminal field size (SP-MF) in HRs, and decrease in BDNF levels accompanied decrease in SP-MF volume in LRs. Epigenetic regulation of neurotrophic support underlying these structural changes is discussed. / by Ozge Oztan. / Thesis (M.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

Adult hippocampal neurogenesis—a unique form of plasticity in the dentate gyrus (DG)—is regulated by experience, and when manipulated can have specific effects on behavior. Different methods have been used over the years to study new neurons’ functional role in the hippocampus, many of which focus on ablating neurogenesis. While ablation methods can test the necessity of adult-born granule cells (abGCs) for behavior, these techniques remove all abGCs from the circuit and thus do not allow one to determine which properties of abGCs are required for behavior. Such information is required to understand the mechanism of their action. Thus, new strategies are needed to determine what properties of young abGCs allow them to distinguish themselves from their mature counterparts and uniquely impact behavior. Recent hypotheses have suggested that the enhanced synaptic plasticity exhibited by 4–6-week-old abGCs allows them to uniquely contribute to hippocampal circuit function, and thus behavior. The primary goal of this thesis was to explore the contribution young abGCs’ heightened synaptic plasticity makes to hippocampal function. This was achieved using a transgenic mouse approach that allowed for the conditional deletion of NR2B from abGCs. Overall, iNR2BNes mice generated the same number of new neurons in adulthood as control mice at baseline. These neurons survived and matured with only a slight reduction in dendritic complexity. However, a potentially important electrophysiological property of these neurons—their enhanced synaptic plasticity—had been eliminated. From an electrophysiological standpoint, iNR2BNes mice resemble mice with ablated neurogenesis, while from all other neurogenic standpoints examined they most closely resemble wild-type mice. Consequently, these mice provided a novel model to test the extent to which young abGCs’ enhanced plasticity contributes to hippocampal-dependent behaviors. The results reveal that eliminating NR2B-containing NMDA receptors from abGCs does not alter baseline anxiety or antidepressant (AD)-like behavior. However, iNR2BNes mice differed from controls in measures of cognitive function. These mice were able to learn in the contextual fear conditioning test, but were impaired in the more difficult contextual fear discrimination test. Mice also exhibited a decreased novelty exploration phenotype that impaired their performance in the novel object recognition test. Together, these results indicate that the NR2B-dependent heightened plasticity exhibited by 4–6-week-old abGCs is necessary for responses to novelty and fine contextual discrimination, but does not contribute to baseline anxiety or emotionality. AD treatment increases levels of adult neurogenesis in the hippocampus, and these newborn neurons have been shown to be necessary for some of the behavioral effects of ADs seen in rodents. In addition, the maturation timeline of adult neurogenesis correlates with the onset of behavioral responses to ADs. ADs also enhance a neurogenesis-dependent form of long-term potentiation (LTP) in the DG evoked by medial perforant path stimulation under intact GABAergic tone called ACSF-LTP. Thus, a potential mechanism by which abGCs may contribute to AD behavioral efficacy is by providing extra plastic units to the DG circuit. This theory was tested by once again using the mouse line in which NR2B can be conditionally deleted from abGCs in the DG. Here, we found that deletion of the NR2B subunit significantly attenuated a neurogenesis-dependent behavioral response to fluoxetine in the novelty suppressed feeding test, and additionally blocked fluoxetine’s ability to enhance young abGCs’ maturation and subsequent integration into the hippocampal network. This suggests that eliminating abGCs’ enhanced plasticity decreases their ability to influence DG output resulting in an AD response that is less robust than seen in control mice. Control experiments revealed the specificity of this effect, as NR2B deletion did not impact the effect of fluoxetine in a neurogenesis-independent behavioral assay (tail suspension test) or in an assay that was insensitive to fluoxetine in this strain of mice (elevated plus maze). Our efforts to isolate the contribution of abGCs’ unique physiology from the neurogenic effects of fluoxetine were not entirely successful as the results presented here also revealed slight group differences in neurogenesis between control mice and mice lacking NR2B in young neurons. Yet, this data still supports the idea that fluoxetine increases the ability of abGCs to participate in DG output by increasing the chance that new neurons will be activated during DG stimulation. This may be achieved either by increasing their overall number, increasing their potential to make synaptic connections, or increasing their ability to strengthen their connections. However, due to the close link between activity and maturation that appears to be enhanced with fluoxetine treatment, a different approach with greater temporal resolution is needed to separate the neurogenic effects of fluoxetine from the physiological contribution abGCs make to hippocampal output. With this in mind, a mouse line in which abGCs could be temporally inhibited was also generated. Cellular and behavioral characterization of mice conditionally expressing hM4Di—a mutated muscarinic acetylcholine receptor that is insensitive to endogenous acetylcholine, but can be activated by the biologically inert, highly bioavailable compound, clozapine N-oxide (CNO)—has begun. Results show that acute CNO treatment in mice expressing this designer receptor exclusively activated by a designer drug (DREADD) in DG granule cells can impair encoding of contextual fear memory. Chronically treating these mice had an anxiogenic effect in the open field test, but otherwise anxiety and emotionality in these mice were comparable to controls. Chronic CNO treatment in mice expressing hM4Di in young abGCs effectively decreased these cells’ dendritic complexity, but did not alter proliferation or early survival. Thus, hM4Di DREADDs represent a novel tool that can be used to modulate activity of neurons in a temporally restricted manner, allowing for both acute and chronic manipulations of hippocampal granule cells. The experiments put forth in this thesis will highlight the importance of abGCs enhanced plasticity. The utility as well as potential pitfalls of the mouse models used here to test theories of abGC function will also be explored. Hopefully this analysis will provide an improved framework in which future experiments can be developed with the aim of uncovering novel insights into the hippocampal circuitry that underlies learning and memory and discovering new strategies for the treatment of neurological and psychiatric disorders.

Zhang Aiqun. / "March 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 95-123). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

The purpose of the current thesis was twofold: (1) to examine various factors that might be contributing to age-related learning and memory deficits specifically related to the hippocampus, and (2) to validate our rat model of aging, employing a multilevel analysis. We found age-related deficits on both spatial and non-spatial hippocampus-dependent taks that were accompanied by structural alterations observed in vivo (volune, but not neuronal metabolic function) and post mortem (neuronal density and neurogenesis, but not synaptic or mitochondrial density). Furthermore, our results suggest that the observed hippocampal structural changes, named decreased volume and neurogenesis, predict learning and memory deficits, and both can be accounted for by neurogenic reduction. In addition, the above-mentioned pattern of age-related deficits closely resembles that seen in humans, suggesting the present rat version of aging to be a very useful model for investigating hippocampal aging in humans. / iii, 236 leaves : ill. (some col.) ; 29 cm.

Different events usually contain similar elements that can contribute to interference during memory encoding and retrieval. The hippocampus (HPC), a structure that is critically involved in some forms of memory, has been hypothesized to reduce interference between memories with overlapping content, thus facilitating correct recall. Pattern separation is one hypothetical process whereby input ambiguity is reduced. Here we test the hypothesis that the HPC and/or dentate gyrus (DG) are important for pattern separation by measuring performance by rats with damage in tasks that require discrimination between visual stimuli that share systematically varying numbers of common elements. Rats with HPC damage were slower to resolve discriminations with minimal degrees of overlap. Lesions of the DG did not affect the ability of rats to deal with overlap, suggesting a dissociation between the HPC and DG. Our results provide partial support for the idea that the HPC contributes to the pattern separation process. / ix, 84 leaves : ill. ; 29 cm.