The hippocampal formation forms a circuit of cytoarchitectonically distinct subregions, and substantial evidence suggests each region makes unique computational contributions that support spatial and episodic memory. With aging, hippocampal subfields undergo unique neurobiological alterations, and primate in vivo work making use of both MR imaging and chronic neural recording devices has important links to changes seen in nonprimate animal models with aging (Thome et al., 2016; Yassa et al., 2011a; Yassa et al., 2010). While MRI offers a noninvasive way to study the hippocampal subfields, identifying hippocampal subregions without using post mortem histology is a challenge. When different research labs attempted to identify the hippocampal subregions using a single subject’s MRI, researchers showed significant disagreement in where to label different subregions (Yushkevich et al., 2015a). Alternatively, chronic neural recording devices offer an invasive solution to studying hippocampal subfields. However, it is currently not clear whether the mechanical trauma and foreign body response produced by neural recording devices disrupts neural circuits critical for behavior. Here, my colleagues and I address these issues with in vivo primate research. Chapter I provides a general introduction to the hippocampal circuits and changes observed in aging. Chapter II presents novel methods for construction of a histology-driven MRI atlas of nonhuman primate hippocampus that addresses accurate identification of hippocampal subfields in MR images. Chapter III presents empirical work that examines whether chronic neural recording devices targeted at the hippocampus affect recognition memory. Finally, Chapter IV provides a general discussion of both works in the context of the broader literature.

The sigma-1 receptors (σ-1Rs) are endoplasmic reticulum (ER) resident proteins shown to have chaperone-like functions, and are widely distributed throughout the central nervous system (CNS). They reside at a specialized membrane called mitochondria- associated ER-membrane (MAM) and can modulate numerous voltage- and ligand-gated ion channels. One of these channels is the N-methyl-D-aspartate receptor (NMDAR), and σ-1R ligands are able to enhance the potentiation of NMDARs, but the mechanism involved remains poorly understood. Using various biochemical techniques, we show that 90 min following an i.p. injection of σ-1R agonists ((+)-SKF 10,047 (SKF), (+)- Pentazocine (PTZ), or PRE-084 (PRE), there is an increase in the expression of GluN2- containing NMDARs in the rat hippocampus. These results suggest that σ-1R activation is able to enhance NMDAR function by modulating protein expression levels both in the cytosol and on the cell surface. This suggests that σ-1Rs could be excellent therapeutic targets for many neurological disorders, and for the development of novel antipsychotics.

Cannabis has been used medicinally for millennia, but the cannabinoid (CB) field exploded with the identification of its endogenous receptors and endocannabinoids (eCBs). In vitro experimentation established that eCBs alter synaptic plasticity at presynaptic nerve terminals; however, the characterization of the eCB system (ECS) in vivo remains incomplete. This study aimed to determine the mechanism of in vivo eCB-mediated hippocampal synaptic plasticity and to analyze the effects this plasticity had on spatial working memory (SWM). With in vivo recordings of field excitatory postsynaptic potentials (fEPSPs) in anesthetized mice and rats as well as pharmacological manipulation of the ECS and glutamate receptor antagonism, it was found that eCBs, both anandamide (AEA) and 2-arachnidonyl glycerol (2-AG), caused LTD at hippocampal CA3-CA1 synapses. Induction of eCB-LTD occurs via a sequential activation of cannabinoid type-1 receptor (CB1R) and NR2B-containing NMDA receptor (NR2BR) and is expressed through the endocytosis of AMPA receptors (AMPARs). Increased eCB tone also caused an impairment of SWM for over 24 hours in the Delayed Non-Match-To-Sample (DNMTS) T-maze. This study provides the first evidence that an acute administration of eCB degradative enzyme inhibitors not only produces an in vivo LTD at hippocampal CA3-CA1 synapses that requires CB1R, NR2BR, and AMPAR, but also impairs SWM, a phenomenon also caused by an acute injection of exogenous CBs.

It is believed that with ageing comes a decline in many cognitive processes, ranging from memory, language and executive function to response inhibition and motor and visual processes. However, memory has attracted much attention and is of particular interest in ageing research. This is because it is a form of cognition that probably suffers the clearest decline with age, and can have a detrimental effect on day-to-day living. Additionally, as people are living longer these problems are affecting an increasing number of people and has therefore become an issue of concern. It is believed that these declines stem from neurophysiological changes that occur alongside ageing. It can be seen that research into this area is of particular importance to better understand the healthy ageing brain, and how illnesses such as Alzheimer's disease differ from this normal progression. The focus of this PhD project addresses this issue by exploring healthy age-related declines in recognition memory and their neural correlates, using brain imaging techniques to investigate underlying changes in brain structure. Novel recognition memory tasks were developed (Chapter 4) to tap underlying processes supporting scene recognition (recollection and familiarity), and were run alongside selected cognitive tasks taken from existing standardised batteries (Chapter 5). In addition to these behavioural measures, MR imaging datasets were collected relating to structural (Chapter 6), perfusion and functional (Chapter 7) as well as diffusion (Chapter 8) measures of the brain. The relationships between these imaging measures were investigated in Chapter 9, in addition to looking at how they related individually to a measure of recollection memory when accounting for the influence each imaging measure had on the others. Overall, age effects were found for the novel recognition memory tasks, in particular showing a significant decline in recollection performance with age. This was associated with a number of neurophysiological measures (functional, perfusion, diffusion and volume) which also showed age-related changes. After taking into account the relative contribution of these measures to task performance, no single imaging measure was found to be a significant predictor of recollection performance.

Orientadores: Iscia Teresinha Lopes Cendes, André Schwambach Vieira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-28T00:14:14Z (GMT). No. of bitstreams: 1 MoratodoCanto_Amanda_M.pdf: 2477839 bytes, checksum: f2e9db3a96d271cc686d6d66697b0e59 (MD5) Previous issue date: 2015 / Resumo: O uso de modelos animais para estudo de doenças humanas é importante para o entendimento dos mecanismos fisiopatológicos destas doenças. Particularmente, os modelos que reproduzem a Epilepsia do Lobo Temporal (ELT) em roedores, apresentam uma epileptogenicidade similar à encontrada em tecidos "epilépticos" humanos quando estudados ex vivo. A ELT afeta cerca de 40% dos pacientes adultos, e é caracterizada clinicamente por um desenvolvimento progressivo de crises epilépticas com foco no lobo temporal. Pacientes que apresentam ELT normalmente não respondem aos tratamentos. Destas, a Epilepsia do Lobo Temporal Mesial (ELTM) e a mais comum e se caracteriza pelo acometimento das estruturas mesiais do lobo temporal, como o caso da Esclerose Hipocampal. A proteômica dispõe de ferramentas poderosas que nos permitem elucidar mecanismos biológicos complexos, encontrar proteínas alteradas em todo o organismo e descrever padrões de expressões proteicas em diferentes condições fisiológicas e patológicas. Portanto, é relevante analisar esse padrão de expressão no hipocampo de modelos animais de ELTM usando técnicas de proteômica, a fim de gerar informações que nos auxiliem no entendimento dos mecanismos envolvidos na epileptogênese desses modelos. No presente estudo, as proteínas identificadas podem nos indicar novas vias envolvidas com a epileptogênese. Além disso, nossos dados demonstram que uma complexidade molecular adicional pode ser observada quando analisamos as diferentes sub-regiões do hipocampo separadamente. Portanto, acreditamos que a integração dos dados de proteômica com dados obtidos por outras "ômicas" podem gerar dados ainda mais informativos sobre esses processos neuronais / Abstract: Studies about human diseases using animal models are really important to our understanding about the physiopathology mechanisms from those diseases. Particularly, the models that reproduce the Temporal Lobe Epilepsy (TLE) in rodents, presents epileptogenicity similar to that found in ex vivo human tissues. The TLE affects around 40% of the adult patients and it is clinic characterized by a progressive development of seizures with temporal lobe focus, caused by an unbalance between the excitatory and inhibitory neurotransmission. Patients who present that type of epilepsy normally don¿t respond well to the treatments. Of this type of epilepsy, the Mesial Temporal Lobe Epilepsy (MTLE) is the most common one and it is characterized by the commitment of the mesial temporal lobe structures, such as in the Hipocampal Sclerosis. To realize these studies the proteomics has many powerful tools that allow us to elucidate complex biological mechanisms, to find altered proteins in the whole organism and describe protein expression patterns in different physiological and pathological conditions. Therefore, it¿s relevant to study this protein expression pattern in the hippocampus of animal models of MTLE using proteomics techniques, searching for informative data that lead us to the understanding of the involved mechanisms in the epileptogenicity. In this study we identified proteins that can indicate new pathways involved in the epileptogenesis processes. Furthermore, our data demonstrate that additional molecular complexity could be observed as hippocampal subfields were analyzed separately. We believe that the further integration of the proteomic data with other "omics" approaches could generate even more informative data about those neuronal processes / Mestrado / Fisiopatologia Médica / Mestra em Ciências

Attention Deficit Hyperactivity Disorder, a disorder marked by a pattern of inattention and hyperactivity, is commonly treated with the drug methylphenidate (MPH), which inhibits reuptake of the neurotransmitters norepinephrine and dopamine, thereby increasing the levels of these catecholamines in the synaptic cleft. In addition, MPH is abused by students studying for exams to increase focus and wakefulness. Despite the extensive use of MPH, little is known its long-term effects on the brain. In this study, we examined the impact of 4 weeks of MPH treatment on neurogenesis or the “birth” of new brain cells in the hippocampus of male adolescent mice. Neurogenesis was measured using 5’-ethinyldeoxyuridine (EdU), a thymidine analog that gets incorporated into DNA before cell division, and total neuron numbers were estimated using the neuronal marker, NeuN. Interestingly, low (1 mg/kg) and high (10 mg/kg) doses of MPH delivered twice daily, increased the rate of neurogenesis after 4 weeks. We also examined the survival of the new cells 4 weeks after EdU injection, both with and without continued MPH treatment. Cell counts were performed, and ratios of EdU+/NeuN+ cells were compared. Although both 1 mg/kg and 10 mg/kg MPH increased the ratio of EdU+/NeuN+ cells, the EdU+/NeuN+ ratios were no different from control if MPH was not continued. If low dose of MPH was continued for an extra 4 weeks, survival of newly generated cells was enhanced; this was not the case for the high dose of MPH. To investigate the mechanism for MPH-induced changes in hippocampal neurogenesis, we examined the levels of proteins linked to cell growth and survival in the hippocampus, including brain derived neurotrophic factor (BDNF), glial cell line derived neurotrophic factor (GDNF), vascular endothelial growth factor (VEGF), tropomyosin receptor kinase B (TrkB, the receptor for BDNF) and beta-catenin. Levels of BDNF or GDNF were examined using enzyme-linked immunosorbent assays (ELISAs), and VEGF, TrkB, and beta-catenin expression was investigated using simple western. Interestingly, 1 mg/kg MPH appears to increase VEGF, TrkB, and beta catenin after 4 weeks. In animals treated with 10 mg/kg MPH, despite the increases in neurogenesis after 4 weeks of treatment, beta catenin levels decreased compared to control at 4 weeks, and VEGF, TrkB and beta catenin levels were decreased at 8 weeks. Thus, long-term exposure to MPH increases neurogenesis rate in the hippocampus, and the effect of low doses of MPH may be related to the increased expression of VEGF, TrkB and beta catenin.

Le projet de thèse s’inscrit dans la continuité de l’étude pilote développée dans le cadre du programme Doremi (Consortium européen de programmes de recherche portant sur les effets des faibles doses). En partant des résultats préliminaires déjà obtenus sur ce projet, l’objectif est d’approfondir les études sur les effets d’une contamination chronique à l’uranium via l’eau de boisson sur le processus de neurogénèse au cours du développement cérébral mais également au stade adulte. La première partie du projet de thèse consiste à comparer la prolifération, la survie et le potentiel de différentiation des cellules des zones neurogéniques (dans l’hippocampe principalement) à l’aide de marqueurs spécifiques de chaque stade de différentiation chez des rats contaminés ou non à l’uranium dès le stade in utero. Cette étude in vivo sera entreprise à différents stades : pendant le développement cérébral embryonnaire et post natal et à l’âge adulte. Cette première partie donnera des pistes pour étudier plus en détails les mécanismes d’action. La deuxième partie du projet de thèse vise donc à étudier comment l’uranium agit sur la neurogénèse à l’aide de modèles in vitro et ex vivo. Des cultures primaires de neurosphères seront utilisées afin d’étudier l’effet de l’uranium sur les capacités de multipotentialité des cellules souches neurales. En parallèle, un modèle de culture organotypique d’hippocampe sera développé. Ce modèle est particulièrement intéressant car il permet de réaliser des expositions aux radionucléides « à façon », d’en étudier les mécanismes d’action dans des aires cérébrales ayant une cytoarchitecture préservée et mettant en jeu différents types cellulaires, tout en combinant des méthodes d’analyse en histologie et en biologie moléculaire. / The PhD project is a continuity of the Doremi program (European Consortium of research programs on low doses effects). The objective is to assess the effects a chronic uranium contamination via drinking water on neurogenesis during brain development and in adult rats. The first part of the project will evaluate proliferation, survival and cell differentiation in neurogenic zones (in particular in the hippocampus) using specific markers for each differentiation stage in control and contaminated rats from the in utero life. This in vivo study will be performed at different stages: during embryonic and postnatal brain development and at the adult age. This part of the project will provide some clues on the potential mechanisms of action that we aim to study more in details. For this purpose, the second part of the project will be performed on in vitro and ex vivo model. Neurosphere primary cultures will be performed to assess uranium effects on the multipotential properties of neural stem cells. We also plan to use a model of hippocampal organotypic culture which will allow the study of the mechanisms of action in a preserved ex vivo structure in terms of cytoarchitecture, cell interactions, and being able to test different uranium concentrations and combine multiple analyses methods (histology, molecular biology…).

Traumatic Brain Injury (TBI) is a global health problem and concussion, or mild TBI (mTBI), accounts for up to 75% of all brain injuries occurring annually in the US. There is also growing awareness that repeated mild traumatic brain injury (r-mTBI) can result in cumulative neuropathology and learning and memory deficits, however there is a paucity of preclinical data as to the extent these deficits manifest. R-mTBI in juvenile populations is of special interest as not only is this a high risk group, but this is also a time period when the human brain continues to mature. The hippocampus is a brain region important for learning and memory processes, and r-mTBI during the juvenile period may particularly disrupt the development of cognitive processes. To examine this issue we used a model of awake closed head injury (ACHI), and administered 8 impacts over a 4 day period to juvenile male and female rats (P25-28). At 1 or 7 days after the last injury, a cohort of rats was used for behavioural testing to study anxiety and risk-taking behaviours and cognitive abilities. From a different cohort, hippocampal slices were generated and used for in vitro electrophysiological recordings, and the capacity for long-term depression (LTD) and long-term potentiation (LTP) was examined in the medial perforant path (MPP)-dentate gyrus (DG) synapse. Our results showed that r-mTBI impaired hippocampal-dependent spatial learning and memory and that r-mTBI significantly impaired the capacity for LTD but not LTP in both sexes. These data are the first to describe the negative impact of r-mTBI on LTD in the juvenile DG in both males and females, and provide evidence for the delayed development of neurological deficits with r-mTBI. / Graduate

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / While memory function in primates depends on the integrity of the medial temporal lobe, the contribution of the hippocampal formation (HF) independent of the overlying ventromedial temporal cortices, particularly the entorhinal (ENT) and parahippocampal (PHG) cortices, remains unclear. To address this issue we have prepared groups of rhesus monkeys with ibotenic acid lesions of the HF or aspiration lesions of the ENT or PHG cortices. We then administered behavioral tasks to assess the effects of these lesions relative to normal controls. To test recognition memory, the Delayed Non-Matching to Sample (DNMS) task and the Delayed Recognition Span Task (DRST) were administered. On DNMS, all groups were impaired on both acquisition and 2 and 10 minute delays. The DRST, administered in Spatial, Color and Object conditions, yielded slightly different results. On the Spatial condition, all groups were impaired on both unique and repeated trials of the task. On the Color condition, all groups were impaired on unique trials while only the HF group was impaired on repeated trials. On the Object condition, ENT and PHG groups were only impaired on unique trials, while the HF group was unimpaired. To assess associative memory, two choice reversals were administered in Spatial (SR) and Object (OR) modalities. On the SR task, The HF group was impaired on acquisition and the first of three reversal phases. The ENT group was impaired on all three reversals, and the PHG group was impaired on only the last. On the OR task, HF animals were impaired on all reversals, while ENT animals were impaired on the initial reversal and PHG animals on the last two. These results indicate that damage to the HF alone causes impairments in recognition, spatial processing and object reversal learning. They also indicate that ENT and PHG regions make unique contributions to memory processes as seen in additional impairments on DRST and the inability to perform spatial reversals. Thus impairments previously attributed to hippocampal damage in studies where the ENT and PHG cortices were removed in conjunction with the HF need to be reevaluated in view of additional contributions provided by these cortical regions. / 2031-01-01

While we have traditionally understood the hippocampus to be involved in memory and navigation, it also appears that it has a role in language processing, creation and prediction. An obvious explanation for this is that language is impossible if linguistic signs cannot be remembered and retrieved. Because linguistic signs are definitionally biologically neutral or arbitrary, we must use the brain's apparatus for learning and storing information from the external world to store and retrieve them. Although plausible, this explanation fails to take into account the hippocampus' role in navigation as a contributing element in the processing, storage and retrieval of linguistic signs. Because the hippocampus also represents non-physical spaces through the same basic cognitive mechanisms with which it represents physical space, it is possible that the semantic content of linguistic signs is encoded in a fundamentally similar way to how navigational information is encoded. If true, this could have implications for education in general, and second language acquisition specifically. These experiments test whether there might be a learning benefit to presenting information in consistent spatial locations by having participants learn word associations in a 3-dimensional virtual environment. The experiments found that this was not the case. These findings have implications for education. Some educational paradigms stress learning in relevant contexts. These results suggest that physical location may not be an important component of a learning environment.