Dissertations / Theses on the topic 'Zif268'

Activity based alterations in synaptic connectivity are thought to underlie the processes involved in learning and memory. Measurable changes in neuronal activation by long-term potentiation (LTP) are widely investigated as a possible cellular correlate of this phenomenon, as it can be induced quickly to elicit long-lasting modifications. These long-term changes in the activity of neuronal circuits are sustained by an altered pattern of gene expression and protein synthesis. The inducible transcription factor Zif268 has been implicated in almost all models of neuronal plasticity. Downstream targets of zif268 are widely believed to contribute to the duration and stabilisation of NMDA receptor dependent LTP which, in turn, can be linked to various models of learning and memory. However, these downstream targets are only just starting to receive attention. By utilising a wide range of contemporary neuroscience techniques covering molecular & cell biology approaches, this thesis proposes two known proteins, gephyrin and ubiquilin, as well as a novel gene (urma), as potential downstream targets of Zif268. Both gephyrin and ubiquilin are associated with GABAA receptors at inhibitory synapses. Gephyrin is thought to cluster and anchor GABAA receptors at postsynaptic sites whilst ubiquilin is reported to regulate receptor surface expression. We found that gephyrin mRNA and protein expression levels were downregulated in response to increased levels of zif268 by transient transfection in PC-12 cells and NMDA stimulation in primary cultured cortical neurones. In addition, ubiquilin mRNA and protein levels were also downregulated within the same experimental paradigms, implying that both gephyrin and ubiquilin are downstream transcriptional targets of this plasticity-related gene. A previously reported microarray experiment (James et al. 2005) contained 144 ESTs significantly affected by the transient transfection of Zif268 in PC-12 cells compared to control. Bioinformatic analyses of these tags revealed interesting genomic areas pertaining to little published information. After further investigation, EST AI169020 revealed a novel transcript that was downregulated in response to NMDA treatment of primary cortical neurones. Additional data mining suggests that urma may be a rarely expressed transcription factor. Basal levels of urma mRNA were also decreased in the Zif268 knockout mouse, as were ubiquilin mRNA levels. Zif268 is a regulatory immediate early gene, activating or suppressing downstream targets that play a role in the duration and stabilisation of LTP. These results indicate that gephyrin and ubiquilin are potential mediators of NMDA receptor-dependent plasticity, by modifying inhibitory-signalling. In addition, Zif268 may actively suppress a novel plasticity-related transcription factor, urma. These findings may underlie important processes in learning and memory.

Les drogues détournent les circuits neuronaux de la récompense et y provoquent des altérations responsables des comportements d’addiction. Ces circuits impliquent les ganglions de la base (GB), qui s’organisent en boucles fonctionnelles formées par les voies directe et indirecte qui contrôlent l’activité de ses structures de sortie. Le point d’entrée des GB est le striatum (STR) qui recoit des afférences glutamatergiques du cortex, et des projections des neurones dopaminergiques. Une activation des récepteurs NMDA et D1 de la dopamine (D1R), déclenche la cascade de signalisation des ERK1/2 dans les neurones striataux de la voie directe et recrute ses cibles, dont le facteur de transcription Zif268 et active la DARPP-32. Tous deux ont des rôles cruciaux dans les effets des drogues. Nous avons cherché à comprendre les rôles de la DARPP-32 et de Zif268 dans les mécanismes d’apprentissage par la nourriture. Nous avons pour cela caractérisé l’expression de Zif268 après des séances d’apprentissage opérant pour de la nourriture dans les deux voies des GB grâce à des souris exprimant la GFP sous la dépendance du promoteur du D1R. Nous avons ensuite mis en évidence une motivation réduite pour ce comportement opérant chez des souris portant une DARPP-32 mutée, ainsi que chez des souris où Zif268 a été invalidé. De plus nous montrons que la surexpression de Zif268 dans le STR dorso-médian est corrélée avec la réponse opérante au début de l’apprentissage opérant. Nous montrons que la DARPP-32 et Zif268 sont des acteurs majeurs dans le système de la récompense. A l’avenir leur étude permettra de mieux comprendre la mise en place de comportements tels que l’addiction ou l’obésité.

La neurogenèse adulte du gyrus denté de l’hippocampe joue un rôle essentiel dans les processus mnésiques dépendants de l’hippocampe, mais son rôle dans des formes complexes de mémoire comme la mémoire épisodique n’a jamais été exploré. Le travail de cette thèse porte sur l’étude de l’implication des nouveaux neurones de l’hippocampe dans la mise en mémoire d’un souvenir épisodique à long terme. Nous avons développé une nouvelle tâche de mémoire épisodique reposant sur la présentation occasionnelle d’épisodes permettant d’encoder des informations de type « Quoi – Où – Dans quel contexte ». Nous montrons pour la première fois que les rats sont capables de se souvenir à très long terme de brefs épisodes de vie et d’utiliser cette mémoire d’une manière flexible. La caractérisation des profils de rétention permet d’accéder aux capacités individuelles de recollection des différents éléments du souvenir et montre que le rappel fiable de la mémoire épisodique nécessite l’intégrité de l’hippocampe et met en jeu un vaste réseau hippocampo-cortical dont l’activation est corrélée au rappel. Les performances de rats soumis à une irradiation focale de l’hippocampe montrent que la neurogenèse adulte hippocampique contribue de façon significative à la consolidation et au rappel fiable du souvenir épisodique. Ces résultats sont discutés dans le cadre d’une implication de la neurogenèse adulte dans la résolution de la mise en mémoire d’événements occasionnels dans le but de discriminer deux épisodes de vie proches, en lien avec les fonctions de séparation et de complétion de patterns de l’hippocampe. Par ailleurs, les mécanismes moléculaires qui sous-tendent le recrutement des nouveaux neurones lors d’un apprentissage restent inconnus. Nous avons analysé le rôle du gène immédiat précoce Zif268, acteur moléculaire essentiel dans les processus mnésiques, et montrons que ce gène joue un rôle crucial dans la sélection et le recrutement des nouveaux neurones lors de la mémorisation au cours de leur période critique d’intégration dans les réseaux neuronaux de l’hippocampe. Ce travail apporte des éléments nouveaux sur la participation des nouveaux neurones hippocampiques dans les processus mnésiques dans une situation à forte demande cognitive basée sur l’encodage d’une représentation intégrée et résolue d’événements occasionnels complexes, ainsi que sur les mécanismes qui sous-tendent leur recrutement
Adult hippocampal neurogenesis plays a critical role in hippocampal-dependent memory, however its role in complex forms of memory such as episodic memory has not as yet been explored. The work presented in this thesis focuses on the issue of the involvement of newborn hippocampal neurons in long term episodic memory. We developed a new episodic memory task based on the presentation of occasional episodes allowing rats to encode “What – Where – In which context” information. We show for the first time that rats are able to remember on the long term brief past episodes of life and to use their episodic memory in a flexible manner. The characterization of retention profiles allows us to identify individual abilities in the recollection of the various elements of the memory and shows that episodic memory recall requires the integrity of the hippocampus and involves a hippocampo-cortical network, the activation of which correlates with recall performance. Performance of rats subjected to focal irradiation of the hippocampus shows that adult hippocampal neurogenesis contributes significantly to the consolidation and faithful recall of episodic memory. These results are discussed in the context of the implication of hippocampal newborn neurons in the resolution of memories of occasional events in order to discriminate different, but closely related episodes of life in relation to pattern separation and pattern completion functions of the hippocampus. Furthermore, the molecular mechanisms underlying the recruitment of newborn hippocampal neurons by learning remain to date unknown. We investigated the role of Zif268, an immediate early gene known to play an essential role in memory processes, and show that this gene plays a crucial role in the selection and recruitment of newborn hippocampal neurons by learning during their critical period of integration in hippocampal neural networks. Overall, this work brings new knowledge on the contribution of newborn hippocampal neurons to memory processes in a highly demanding cognitive situation based on the encoding of an integrated and high-resolution representation of complex occasional events, and on the mechanisms underlying their recruitment

BACKGROUND:Aging is typically accompanied by memory decline and changes in hippocampal function. Among these changes is a decline in the activity of the dentate gyrus (DG) during behavior. Lasting memory, however, is thought to also require recapitulation of recent memory traces during subsequent rest - a phenomenon, termed memory trace reactivation, which is compromised in hippocampal CA1 with progressive age. This process has yet to be assessed in the aged DG, despite its prominent role in age-related memory impairment. Using zif268 transcription to measure granule cell recruitment, DG activity in adult and aged animals was assessed both during spatial exploration and as animals remained at rest in the home cage in order to detect potential memory-related replay.RESULTS:Consistent with the observation of memory trace reactivation in DG, the probability that an individual granule cell transcribes zif268 during rest in the animal's home cage is increased by recent experience in a novel environment. Surprisingly, a comparable increase was observed in the probability of granule cells in the aged DG expressing zif268 during rest. Moreover, no significant age-related difference was observed in the number of granule cells expressing zif268 during rest. Thus, the number and pattern of granule cell expression of zif268 during rest is preserved in aged animals, despite a significant decline in exploration-related zif268 expression.CONCLUSIONS:These data lead to the hypothesis that the input the aged DG receives from backprojections from CA3 (the region widely hypothesized to mediate reactivation) remains functionally intact despite loss of innervation from the perforant path.

Thesis (S.M.)--Massachusetts Institute of Technology, Biological Engineering Division, 2006.
Includes bibliographical references (p. 42-43).
Optical tweezers instruments use laser radiation pressure to trap microscopic dielectric beads. With the appropriate chemistry, such a bead can be attached to a single molecule as a handle, permitting the application of force on the single molecule. Measuring the force applied in real-time is dependent on detecting the bead's displacement from the trapping laser beam axis. Back-focal-plane detection provides a way of measuring the displacement, in two-dimensions, at nanometer or better resolution. The first part of this work will describe the design of a simple and inexpensive position sensing module customized for optical tweezers applications. Single molecule fluorescence is another powerful technique used to obtain microscopic details in biological systems. This technique can detect the arrival of a single molecule into a small volume of space or detect the conformational changes of a single molecule. Combining optical tweezers with single-molecule fluorescence so that one can apply forces on a single molecule while monitoring its effects via single molecule fluorescence provides an even more powerful experimental platform to perform such microscopic studies. Due to the enhanced photobleaching of fluorophores caused by the trapping laser, this combined technology has only been demonstrated under optimized conditions.
(cont.) The second part of this work will describe a straightforward and noninvasive method of eliminating this problem. The study of mechanotransduction in biological systems is critical to understanding the coupling between mechanical forces and biochemical reactions. Due to the recent advances in single molecule technology, it is now possible to probe such mechanisms at the single molecule level. The third and final part of this work will describe a basic mechanotransduction experiment using the well-studied ZIF268 protein-DNA system. An experimental assay and method of analysis will be outlined.
by Peter Lee.
S.M.

On admet généralement que la mémoire à long terme repose sur des d'efficacité synaptique dans les réseaux neuronaux activés par l'apprentissage et que cette plasticité dépend de régulations transcriptionnelles. Nous nous sommes attachés à caractériser le rôle du gène immédiat précoce zif268 dans la plasticité synaptique et dans les processus de consolidation et de reconsolidation mnésique, et de situer sa place dans la cascade de signalisation impliquant le facteur de transcription CREB, par l'utilisation de souris génétiquement modifiées. Des analyses électrophysiologiques montrent que l'invalidation du gène zif268 n'altère pas la transmission synaptique dans le gyrus denté de l'hippocampe, mais que la potentialisation à long terme (LTP) ne peut se maintenir au-delà de 24h, suggérant que zif268 est nécessaire au maintien des phases tardives de la LTP. L'étude de différentes formes de mémoires montre que l'invalidation de zif268 empêche la formation d'une mémoire à long terme dans des tâches spatiales et non spatiales, sans altérer la mémoire à court terme. Ce déficit de consolidation est soumis à un effet de dosage génique dépendant du type d'apprentissage mais peut cependant être compensé par un apprentissage distribué et intensif. Nos résultats montrent aussi que l'inactivation fonctionnelle de CREB chez des souris transgéniques conditionnelles, comme l'inactivation de zif268, provoque un déficit de mémoire de reconnaissance à long terme. Enfin, nous avons examiné l'implication de zif268 dans les processus de reconsolidation d'une mémoire de reconnaissance après rappel. En l'absence de zif268, lorsque l'on réactive une trace précédemment consolidée, cette dernière n'est pas reconsolidée, conduisant à un déficit de rappel ultérieur. Ces résultats mettent en évidence le rôle crucial du gène zif268 dans le maintien à long terme de la plasticité synaptique hippocampique ainsi que dans la consolidation et à la reconsolidation mnésique
It is a commonly accepted premise that long-term memory is based on persistent changes in synaptic strength in neuronal networks activated by learning and that plasticity relies on transcriptional regulation. Here we have focused on the potential roles primarily of the immediate early gene zif268 and to a lesser extent, the transcription factor CREB, in long-lasting synaptic plasticity and in the processes of memory consolidation and reconsolidation, using genetically modified mice. Our electrophysiological analyses show that invalidation of zif268 does not impair synaptic transmission in the dentate gyrus of the hippocampus, but that long-term potentiation (LTP) does not persist beyond 24h, suggesting zif268 is necessary for the maintenance of the late phases of LTP. Our behavioural experiments show that invalidation of zif268 prevents the formation of a long-term memory in both spatial and non-spatial memory tasks, without effecting short-term memory. This consolidation deficit relies on a task-dependent gene-dose effect, but the deficit can be compensated for by an extended and distributed learning. Our results also show that functional inactivation of CREB in conditional transgenic mice leads, as shown with inactivation of zif268, to long-term recognition memory impairment. Finally, we examined the implication of zif268 in the process of reconsolidation of recognition memory after reactivation of the memory trace. Although with extended training zif268 mutant mice have normal recognition memory when tested 5 days later, if the memory trace is reactivated after learning they are unable to reconsolidate the information, leading to a deficit in later recall. These results show a critical role of zif268 in the maintenance of long-term synaptic plasticity in the hippocampus and in memory consolidation and reconsolidation under optimal conditions

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Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
In the present work, we investigated behavioral changes associated with the increase in Zif268 protein expression within telencephalic areas of the tropical lizard Tropidurus hispidus that correspond to the mammalian hippocampus (HC). We used 13 male individuals of this species, collected at the Federal Agrotechnical School of Rio Grande do Norte, under SISBIO license number 19561-1. Four animals had their brains removed and were submitted to a Western blot with antibodies for the Zif268 protein. The remaining animals were separated in two different groups: a control group (n=4) and an exploration group (n=5). Animals from the exploration group were exposed to an enriched environment with many sensory cues novel to them. Control group animals stayed in the environment they were already habituated to. After 90 min from the onset of exposure to the new environment, animals from both groups were submitted to intracardiac perfusion with fixative, and the brains were removed, cryoprotected and frozen. After that, brains were sectioned at 20 μm and the sections were subjected to immunohistochemistry for the Zif268 protein. We verified that the Zif268 protein is likely conserved in the brain of T. hispidus, which showed antigenicity for the antibody anti-Zif268 made in mammals. In animals from the exploration group, we detected an increase of the Zif268 protein in the Septum, Striatum, Dorsoventricular Area and in cortical areas corresponding to the HC. This increase was proportional to the amount of environmental exploration, with maximum positive correlation in the hippocampal subareas Medial Cortex (R = 0.94 and p = 0.004) and Dorsomedial Cortex (R = 0.92 and p = 0.006). The data corroborate the notion that the reptilian hippocampus, as well as the mammalian HC, plays an important role in spatial exploration.
Neste trabalho, foram investigadas altera??es comportamentais associadas ao aumento da express?o da prote?na Zif268 em ?reas telencef?licas do lagarto tropical Tropidurus hispidus correspondentes ao Hipocampo (HC) de mam?feros. Foram utilizados 13 animais machos do lagarto T. hispidus, coletados no campus da Escola Agrot?cnica Federal do RN, sob a licen?a do SISBIO (n.19561-1). Quatro animais tiveram seus c?rebros removidos a fresco e submetidos a Western blot com anticorpo para a prote?na Zif268. Os animais restantes foram separados em dois grupos distintos, grupo controle (n=4) e grupo explora??o (n=5). Animais do grupo explora??o foram expostos a um Ambiente Enriquecido (AE) com diversas pistas espaciais desconhecidas pelos animais. Os animais do grupo controle permaneceram no ambiente ao qual j? estavam previamente habituados. Transcorridos 90min do in?cio da exposi??o ao ambiente, animais de ambos os grupos, foram submetidos a perfus?o intracard?aca com fixador, e os c?rebros foram removidos crioprotegidos e congelados. Posteriormente os c?rebros foram seccionados a 20μm e submetidos ? imunohistoqu?mica para Zif268. Verificamos a conserva??o da prote?na Zif268 no c?rebro do T. hispidus, com antigenicidade para o anticorpo anti-Zif268 produzido em mam?feros. Nos lagartos do grupo explora??o detectou-se aumento da express?o da prote?na Zif268 no Septo, Estriado, ?rea Dorsoventricular e ?reas corticais que correspondem ao HC (C?rtices Medial CM, Dorsal CD, Dorsomedial CDM). Esse aumento ? proporcional ? explora??o do ambiente novo, com m?xima correla??o nas sub?reas hipocampais do grupo explora??o, C?rtex Medial (R = 0,94 e p = 0,004) e Dorsomedial (R = 0,92 e p = 0,006). Os dados corroboram a no??o de que o hipocampo reptiliano, assim como o HC de mam?feros, desempenham um papel importante na explora??o de novos ambientes.

Durant ma thèse, j’ai étudié dans le bulbe olfactif (BO) de souris adulte, les mécanismes cellulaires et moléculaires impliqués dans l’apprentissage et de la mémorisation olfactive. Le BO est le premier relai central de l’information olfactive. A ce niveau, des phénomènes de plasticité locaux interviendraient dans la conservation d’une trace mnésique de l’apprentissage. J’ai tout d’abord évalué, dans la couche granulaire, les conséquences d’un apprentissage olfactif associatif sur l’expression de l’IEG Zif268 induite par une stimulation odorante. Les souris ayant une expérience préalable avec l’odorant ne présentent pas d’augmentation de l’expression de Zif268. Cependant, le patron d’expression cellulaire de Zif268 est modifié par l’apprentissage. J’ai ensuite isolé par microdissection laser, à partir des patrons d’expression de Zif268, les populations de cellules de la couche granulaire impliquées dans le traitement de l’odorant suite à l’apprentissage. Dans ces régions, l’étude de l’expression des gènes à large échelle m’a permis de mettre en évidence que la voie des neurotrophines était modulée dans la phase précoce de l’apprentissage alors que les acteurs de la LTP étaient modulés lors de la phase tardive. Enfin, j’ai montré que des souris inactivées pour zif268 présentaient des déficits d’acquisition et de consolidation de l’apprentissage olfactif ainsi que de discrimination d’odorants perceptivement proches. Ces résultats indiquent que l’acquisition par l’odorant d’une signification lors d’un apprentissage olfactif modifie son traitement dans le BO. D’autre part, des acteurs moléculaires potentiellement impliqués dans ces modifications cellulaires ont été identifiés
My research was about cellular and molecular mechanisms implicated in olfactory learning and memory in the adult mouse olfactory bulb (OB). The OB is the first relay of olfactory information in the central nervous system. At this level, phenomenon of local plasticity could be involved in the conservation of a memory trace associated with learning process. First, I evaluated in the granule cell layer, the consequences of an olfactory associative learning on the IEG Zif268 odour-induced expression. Mice with a prior behavioural experience with the odour do not show increase in Zif268 expression. However, the specific odour-induced Zif268 expression pattern is modified by learning. Then, I isolated using laser capture microdissection activated cell populations of the granule cell layer, based on Zif268 expression patterns, after an olfactory associative learning. In those regions, I studied gene expression at a large scale. I found that neurotrophine pathway was modulated during the early phase of learning process whereas molecular actors of LTP are modulated during the consolidation phase. Finally, I showed that Zif268 knock-out mice exhibit associative learning and memory deficits. Those mice also present deficits to discriminate between closely related odorants. Those results indicate that acquisition by odorant of a behavioural meaning during olfactory learning modify odorant processing at the level of OB. Moreover we identified candidate genes that could be implicated in the cellular modifications

Notre travail de thèse analyse, par des approches comportementales et neuro-anatomique, l'impact du vieillissement sur le processus d'aversion olfactive potentialisée par le goût (AOPG). Des rats jeunes, adultes et sénescents sont soumis à l'acquisition et au rappel de cet apprentissage. Tous les rats sont capables d'acquérir et de se rappeler cet apprentissage, même si on note une altération, en fonction de l'âge, de leurs capacités cognitives évaluées par trois tâches différentes. Les expressions de Fos et de Zif268, après rappel de l'AOPG, mettent en évidence des patterns d'activation cérébrale différents en fonction du stimulus (odeur ou goût) utilisé pour le rappel et qui, de plus, évoluent avec l'âge. Ce travail nous a permis de proposer un modèle fonctionnel de l'AOPG.

Dans ce travail, nous démontrons que STIM1, un senseur calcique activé par la déplétion du Ca2+ intracellulaire du réticulum endoplasmique, est indispensable pour la signalisation calcique et la préférence oro-sensorielle du gras. Nous observons que l'acide linoléique (LA), en activant les phospholipases A2 via CD36, produit de l'acide arachidonique (AA) et de la lyso-phosphatidylcholine (lyso-PC). Cette activation déclenche un influx calcique dans les cellules CD36-positives, et induit la production du facteur CIF (Ca2+ Influx Factor). CIF, AA et lyso-PC exercent différentes actions sur l'ouverture des canaux SOC (Stored Operated Calcium Channel) constitués de protéines Orai et contrôlés par STIM1. Par ailleurs, les souris au phénotype Stim1-/- perdent la préférence spontanée pour les lipides et la libération de la sérotonine à partir des cellules gustatives dans le milieu extracellulaire chez les animaux sauvages. Nous demontrons aussi que la signalisation calcique médiée via CD36 est doublement modulée lors de l'obésité. L'augmentation de la [Ca2+]i dans les cellules gustatives observée chez le Psammomys obesus, un modèle d'obésité nutritionelle, est fortement diminuée chez les souris rendues obèses par un regime hyperlipidique. Nous avons constaté également que l'interaction de LA avec le CD36 induit l'activation des MAP Kinases de la voie MEK1/2/ERK1/2/Elk-1 qui est non seulement à l'origine de l'activation des aires cérébrales telles que le NTS, le noyau arqué, l'hippocampe mais aussi indispensable pour la préférence spontanée pour les lipides alimentaires. Nos résultats suggèrent pour la prémière fois, que la voie ERK1/2 des MAPK et la signalisation calcique lipidique controlée par STIM1 sont impliquées dans la perception oro-gustative des lipides

The crystal growth of nanoporous materials is different from most other classes of material in that their framework architectures contain periodic arrangement of pores or voids in which there is no direct bonding between adjacent units of the framework. This poses a variety of questions as to how such parts of framework develop during the crystallization process, atomistically and energetically. Here we use the nanoporous metal-organic framework, ZIF-8 as a prototypical material to obtain a basic understanding of the growth of a nanoporous material. The crystals of ZIF-8 produced in the N,N-dimethylformamide solvent [ZIF-8(DMF)] and methanol-co-N,N-dimethylformamide solvent [ZIF-8(MeOH)] are both rhombic dodecahedron in shape with a much smaller crystal size in the latter. In the study of the kinetics of ZIF-8(DMF) crystallization, we get a good agreement in the values of activation energies using both Avrami-Erofe’ev-Hancock-Sharp and Gualtieri’s models, i.e. about 120 kJ mol-1 for nucleation, and 95 kJ mol-1 for crystal growth process. The study of kinetics of ZIF-8 surface growth, by in situ AFM, with ZIF-8(DMF) as seed crystal that are grown in the methanolic growth solution we see faster rate in the <100> directions than the <110> directions, with the most probable activation energy of about 80 kJ mol-1 in both directions. This is the first example of in situ AFM being used to obtain activation energy for a surface growth in MOF. We also reveal here that growth process of ZIF-8 occurs through the nucleation and spreading of successive metastable unenclosed sub-steps to eventually form stable terrace steps of the enclosed framework structure in which this process is reliant on the presence of nonframework species to connect the framework species that have voids between them. The experiments also enable identification of some of the fundamental units in the growth process and the stable crystal surface plane. Further, the spreading of terraces at high supersaturation condition (early state) is fairly isotropic as is seen through the formation of almost-rounded terraces on the surface of ZIF-8. The growth direction becomes clear as the supersaturation condition nears to equilibrium (later stage) by the formation of rhombohedral terraces with pointy ends growing along the <100>, and <110> directions and straight edges growing perpendicular to the <111> direction. Formation of this rhombohedral morphology is explained by a coarse grain approach similar to that used in the Kossel model by making assumptions that the sodalite cage is the growth unit and attachment of one sodalite cage in each growth direction is the rate determining step for the formation of a new row of sodalite cages in each direction. Finally, based on the profiles of growth spirals formed from screw dislocations on the ZIF-8 surface obtained from the ex situ AFM images and ICE theory, plausible screw dislocations with Burgers’ vector of 1/2 <111> and <100>, but not <110>, are deduced. Some of the findings in this work will be applicable to numerous nanoporous materials, and the work in general will support efforts to synthesize and design new framework materials and to control the crystal properties of these materials.

碩士
國立臺灣師範大學
生命科學研究所
95
In recent years, many neuroscience scientists concern about the neural mechanisms of the extinction of conditioned fear. They hope to investigate the mechanisms to know more about the neural plasticity, and can use to treat the clinical anxiety disorders. Recent results suggest that the amygdala plays a key role in fear extinction, and an important component of extinction is activation of glutamatergic NMDA receptors in amygdala. Scientists used systemic administration and direct amygdalar infusion of D-cycloserine (DCS), one of partial NMDA receptor agonists, into rats can facilitate extinction. And the facilitation is activated by the mitogen activated protein kinase (MAPK) signal transduction pathway. However, the mechanisms of downstream regulation are unknown. zif268 belongs to the category of immediate early genes (IEG), act as a transcription factor, zif268 protein, Zif268, can be activated by many stimulus. When once it is translated, it transports into nucleus immediately, controls expression of other genes, and associates synaptic plasticity. Recent studies suggest that zif268 plays a critical role in formation of conditioned fear memory. In this study, we used fear-potentiated startle and direct amygdalar infusion of zif268 antisense oligodeoxynucleotide to investigate whether facilitating extinction of fear memory by DCS is related to the expression of zif268. Our results shown that administration of DCS 30 minutes prior to the extinction training can facilitate the expression of extinction. Direct amygdalar infusion of zif268 antisense oligodeoxynucleotide 90 minutes prior to the extinction training can block the expression of extinction facilitated by DCS and also decrease the expression of Zif268 protein. Our study provide evidence that the facilitation of DCS effect on the extinction of conditioned fear is meditated by zif268. It starts downstream signal transduction pathway and alters synaptic plasticity. We expect that the study will contribute to the development of new treatment for anxiety disorders.

Adolescence is a critical period for drug addiction in humans. Most lifelong drug addiction is initiated during adolescence and the progression from initial drug use to the expression of addictive behaviors occurs more rapidly during adolescence than in adulthood. The purpose of this work was to examine if the adolescent brain uniquely responds to the addictive stimulant cocaine. This was accomplished by comparing the following measures in adolescent and adult male rats: locomotor responses to cocaine across a range of doses in two acute cocaine binge models, plasma cocaine and brain concentrations, locomotor responses to apomorphine, the relative magnitude of locomotor sensitization induced by a single high dose of cocaine (40 mg/kg), and cocaine-induced c-fos and zif268 expression. We determined that young adolescent (PN 28) rats had greater stereotypy responses to all doses of a repeated dose cocaine binge (15 mg/kg), the highest dose of an escalating dose binge (25 mg/kg), and low dose apomorphine. In addition to showing exaggerated acute locomotor responses to cocaine, young adolescents demonstrated a form of intrabinge sensitization that was absent in adults. Exaggerated adolescent locomotor responses could not be attributed to cocaine metabolism as we did not observe greater cocaine plasma or brain concentrations in adolescents compared to adults. A single high dose of cocaine (40 mg/kg) induced more ambulatory and stereotypy sensitization in young adolescents than adults. Further, the magnitude of the acute locomotor response to cocaine predicted the magnitude of locomotor sensitization in individual adolescents. We also showed that cocaine dose-dependently caused age-specific increases in the expression of the plasticity-associated immediate early genes c-fos and zif268: low dose (10 mg/kg) cocaine caused greater increases in striatal c-fos expression in adolescents whereas high dose (40 mg/kg) cocaine caused greater increases in striatal c-fos and zif268 expression in adults. Both doses of cocaine stimulated bigger increases in cortical zif268 expression in adults compared to adolescents. Finally, we demonstrated that the coordinated expression of striatal c-fos and zif268 develops during adolescence: there was no correlation between striatal c-fos and zif268 expression in individual adolescents but a strong correlation was seen in adults. The results of these experiments demonstrate that adolescents have unique molecular responses to acute cocaine and may help explain how adolescents show unique adaptive changes following continued cocaine use.

Dissertation

abstract: ABSTRACT Auditory hallucinations are a characteristic symptom of schizophrenia. Research has documented that the auditory cortex is metabolically activated when this process occurs, and that imbalances in the dopaminergic transmission in the striatum contribute to its physiopathology. Most animal models have focused the effort on pharmacological approaches like non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists to produce activation of the auditory cortex, or dopamine antagonists to alleviate it. I hypothesize that these perceptual phenomena can be explained by an imbalance activation of spiny projecting neurons in the striatal pathways, whereby supersensitive postsynaptic D2-like receptor, signaling in the posterior caudatoputamen generates activation of the auditory cortex. Therefore, I characterized the neuroanatomical component involved in the activation of the auditory cortex. I evaluated the participation of dopamine D2-like receptor using selective dopamine antagonist manipulations and identified the circuits related to the auditory cortex by retrograde trans-synaptic tracing using pseudorabies virus (PRV-152). My results show that dopamine infused in the posterior caudatoputamen dose dependently increases the transcription of the immediate early gene, zif268 in the auditory cortex, predominantly in layers III and IV, but also in cortical columns, suggesting enhanced functional auditory activity. This indicates the participation of the posterior striatum in the modulation of the secondary auditory cortex. I was able to demonstrate also that a coinfusion of a selective dopamine D2-like receptor antagonist, eticlopride and dopamine, attenuate the activation of the auditory cortex. Furthermore, using PRV-152 I delineate the distinctive circuit by axial mapping of the infected neurons. Thus, I found secondary projections from the posterior caudatoputamen that synapse in the thalamus before reaching the auditory cortex. These striatal projections correspond to the same brain region affected by dopamine during auditory cortical activation. My results further characterized a mechanism to generate intrinsic perception of sound that may be responsible for auditory hallucinations. I propose this paradigm may elucidate insight on the biological basis of psychotic behavior.
Dissertation/Thesis
Figure 9C. 3D brain reconstruction after 48 hours of PRV-152 inoculations
Figure 9A. 3D brain reconstruction after 24 h postinoculation
Figure 9B. 3D brain reconstruction after 36 h postinoculation
Doctoral Dissertation Neuroscience 2014

博士
國防醫學院
生命科學研究所
96
Serum- and glucocorticoid-inducible kinase 1 (SGK1) has been shown to play an important role in spatial memory formation, but the underlying molecular mechanism is not known. In the present study, the hypothesis that SGK1 regulates transcription of the immediate early gene zif268, a transcription factor that is essential for memory formation, was tested. The mechanism for SGK1-regulated zif268 expression in relation to the transcription factors, SRF, Elk-1, and CREB1, was also studied. Results revealed that transfection of the dominant negative mutant of SGK1, SGK1 S422A, to rat hippocampal CA1 area significantly decreased the mRNA level of zif268 induced by water maze learning. SGK1 was found to phosphorylate SRF at Ser73, Ser75 and Ser99, and phosphorylate CREB1 at Ser133. Inhibition of phosphorylation at these residues with alanine substitution significantly diminished SGK1-enhanced zif268 expression. SGK1 also phosphorylated Elk-1 at Ser159 and Thr160, but it did not affect SGK1-enhanced zif268 expression. Substitution of these residues with aspartate to mimic SGK1 phosphoryltion of Elk-1 decreased the transcriptional activity of Elk-1, suggesting that SGK1 may negatively regulate Elk-1. Moreover, phosphorylation of SGK1 at Ser422 was increased in rat hippocampal CA1 area after water maze learning, accompanied by increased phosphorylation of SRF at Ser99 and CREB1 at Ser133. These effects were antagonized by transfection of SGK1 S422A. These results suggest that SGK1 enhances zif268 expression through the mediation of SRF and CREB1. These signaling pathways are probably involved in spatial memory formation.

L'objectif de ce travail a été d'étudier deux aspects de la flexibilité du système des cellules de lieu de l'hippocampe : la réponse adaptative des cellules de lieu à des changements environnementaux, et les aspects moléculaires impliqués dans cette flexibilité. Dans une première étude, nous avons évalué la capacité de ces cellules à maintenir une représentation spatiale stable malgré des changements des repères de l'environnement. Nous avons pour cela produit un conflit en tournant deux types d'indices dans des directions opposées : des indices proches et des indices distants. La majorité des cellules montre une réorganisation de la représentation (remapping), ce qui suggère qu'elles sont contrôlées par la configuration d'ensemble des indices. Moins souvent, les cellules sont contrôlées par les indices proches, et encore moins souvent par les indices distants. En retirant un des ensemble d'indices, nous observons la compétition entre les processus de pattern completion et pattern separation. Dans un deuxième ensemble d'études, nous avons cherché à comprendre l'implication du gène zif268 dans la mémoire spatiale à court terme et à long terme. Ce gène, membre de la famille des facteurs de transcription Egr, jouerait le rôle de « commutateur moléculaire » permettant le remodelage durable des réseaux neuronaux à la base de la formation de traces mnésiques stables, qui a lieu lors des processus de potentialisation à long terme (PLT). Nous avons testé une souche de souris mutantes chez laquelle le gène zif268 (Krox24) est invalidé dans l'ensemble du cerveau. D'abord, nous avons voulu identifier comment ce gène contrôle la stabilité des champs d'activité des cellules de lieu de CA1 hippocampiques. Nos résultats montrent que les souris mutantes zif268 ont des cellules de lieu fonctionnelles, avec des paramètres de décharges comparables aux souris contrôles. Nous avons trouvé que la délétion de ce gène n'interfère pas avec la formation, ni avec le maintien à court terme (1h) d'une nouvelle représentation, mais affecte seulement son maintien à long terme (24h). Zif268 est donc nécessaire pour le maintien à long terme de la représentation spatiale. Ensuite, dans une tâche d'exploration d'objets, nous avons montré que les souris mutantes zif268 présentaient des déficits dans la détection d'un changement spatial, après la réactivation du contexte initial, ce qui suggère un rôle de zif268 dans la re-consolidation. Ensemble, ces résultats indiquent que zif268 est un élément clef de la voie de signalisation moléculaire responsable de la formation de souvenirs à long terme.