Fragile X Syndrome (FXS) is the leading cause of inherited intellectual disability. The disorder is caused by a trinucleotide expansion that silences the Fragile X Mental Retardation 1 (Fmr1) gene resulting in the loss of its protein product, the Fragile X Mental Retardation Protein (FMRP). FXS patients show broad clinical phenotypes including intellectual disability, as well as a number of cognitive and behavioral problems. The lack of FMRP is believed to be the direct cause of the deficits seen in FXS patients. FMRP is an RNA-binding protein that is expressed in the brain and testes. This protein is believed to form a messenger ribonucleoprotein complex with mRNAs in the nucleus and subsequently export them to polyribosomes in the cytoplasm, therefore influencing translation of its bound mRNAs. Importantly, FMRP has long been suspected to be involved in synaptic plasticity due to its ability to bind several mRNAs that encode for proteins important in synaptic plasticity. Such proteins include the GluN1, GluN2A and GluN2B subunits of the N-methyl-D- aspartate receptor (NMDAR). FMRP is expressed in the hippocampus, a region of the brain involved in learning and memory processes. Recently, impaired NMDAR functioning in the dentate gyrus (DG) subregion of the hippocampus has been observed in Fmr1 knockout (-/y) mice. This impairment also resulted in reduction in long-term potentiation (LTP) and long-term depression (LTD) of synaptic efficacy, two biological models of learning and memory. In the present study, I focused on the levels of the NMDAR GluN1, GluN2B and Glu2B subunits in order to determine the synaptic plasticity alterations seen in the DG of Fmr1-/y mice. Using Western blotting, I found that there is a decrease in the GluN1, GluN2A and GluN2B subunits in the DG of young adult Fmr1-/y mice, indicating that these mice have significantly lower amounts of total NMDARs. These results could explain the altered LTP and LTD seen in Fmr1-/y mice at the molecular level and might contribute to the intellectual impairments seen in these KO mice. NMDARs appear to be important in the development and maturation of synapses. The GluN2A and GluN2B subunits are developmentally regulated, where GluN2B is predominantly expressed early in development and GluN2A in the adult brain. A dysregulation of GluN2A and GluN2B subunits has been proposed to affect the maturation and formation of synapses. Intriguingly, FMRP is also believed to play a functional role in early brain development. Thus, this study also focused on the developmental expression of the GluN1, GluN2A and GluN2B subunits in the DG, Cornu Ammonis, prefrontal cortex and cerebellum of Fmr1-/y mice, all of which are brain regions implicated in FXS. We found that the developmental expression of these subunits is altered in Fmr1-/y mice in specific brain regions. Together, these results demonstrate that the loss of FMRP differentially affects GluN1, GluN2A and GluN2B subunit expression both developmentally and spatially, further implicating NMDARs in the pathophysiology of FXS. / Graduate

Thesis (Ph.D. in Pharmacology) -- University of Colorado Denver, 2008. / Typescript. Includes bibliographical references (leaves 100-118).

Philosophiae Doctor - PhD / It was postulated that each gene has three main sets of transcriptional elements: one which is gene-specific, one which is family-specific, and a third which is tissue-specific.The starting hypothesis for this project had been: “Each family of genes has a distinct set of transcriptional elements that is unique onto this family”. The primary aim of this project was therefore the identification of the family-specific set of transcriptional elements within the AMPA receptor gene family. The question then is how does one measure or identify this uniqueness within the promoters of this family of genes. The answer seemed to lie in making an assessment of the promoters of this family of genes against a background of a comprehensive set of promoter sequences and in the process,to try to find the transcriptional elements that were present in the AMPA receptor gene promoters but were not so common in the general population of gene promoters.To achieve the primary aim of this project, it was essential that a comprehensive dataset of promoter sequences was available. There are ample data freely available through the web. However, it is often not available in a form that we might want it in. Another problem that one constantly encounters is the lack of general consensus among the research community in agreeing on a standard annotation. For example, a gene can sometimes be given 2 or 3 different names by different laboratories which have successfully cloned the same gene. This, in turn, hinders the data collection process. At the start of this project, there was an existing curated database of experimentally-verified eukaryotic promoter sequences called the Eukaryotic Promoter Database (EPD) and a software called Promoter Extraction from GenBank (PEG) which, as its name implies, extracts promoter sequences available through GenBank (Cavin Périer et al., 1998;Zhang & Zhang, 2001; Praz et al., 2002; Schmid et al., 2004). However, limitations existed in both these resources. For EPD, the number of curated promoter sequences available was low and also, the length of these promoter sequences was short. For PEG,the main limitation was that the extraction from GenBank would result in extraction of sequences of variable lengths.Therefore, the 5’-end Information Extraction (FIE)system was developed for the expressed purpose of collecting promoter sequences without the limitations of PEG. This software relies on the alignment of multiple mRNA/cDNA sequences that are representative of a gene on the human genomic sequence to determine the transcription start site (TSS) of the gene and thus, with this information, extract the promoter sequence for the gene from the available human genomic sequence. This was the first promoter extraction software to work on this principle (Chong et al., 2002). This method was later supported by experimental work carried out by Coleman and colleagues (2002). Using the FIE2 software (Chong et al.,2003), some 10,000-odd human promoter sequences was extracted, starting at 1500bp uptream and ending at 1000bp downstream of the 5’-most TSS.Following the collection of the human promoter sequences, the approach developed by Bajic et al. (2004) was applied to study the promoters of the AMPA receptor genes. This approach relies on both the MATCH program to map putative transcription factor binding sites (TFBSs) to the promoter sequences and a software developed by Bajic etal. (2004) that calculates to the density for each TFBS or composite element. Having calculated the densities for the TFBSs and composite elements for both the target promoters (in this case, the AMPA receptor gene promoters) and the background promoters (the 10,000-odd human promoters), the software then calculates the degree of over-representation of each TFBS and composite element in the target promoters(measured against the background promoters) and then ranks the “singles”, “pairs” and “triplets” in the order of their degree of over-representation. Using this method, I identified the top 3 ranked “single”, “pair” and “triplet” transcriptional elements found commonly within the AMPA receptor promoters. In addition, a conventional phylogenetic footprinting study was also carried out for the human, mouse and rat GRIA1 promoter to identify key transcriptional elements within this subunit’s promoter.While the approach developed by Bajic et al. (2004) identifies key family-specific transcriptional elements, the phylogenetic footprinting study helps identify key genespecific transcriptional elements. Thus, they complement one another.The approach developed by Bajic et al. (2004) yielded an interesting result. It was found that the combination of the top 3 ranked “single”, “pair” and “triplet” transcriptional elements found in the AMPA receptor promoters were also found in 47 other genes. It was postulated that these 47 genes might, in fact, be co-regulated / co-expressed with the GRIAs and thus, explaining the existence of a shared promoter profile with the GRIA promoters. In support of this hypothesis, supporting evidence was found in published literature that 7 of these 47 genes (VAMP4, Rab3B, FKBP8, 3-OST-3A, CLSTN3,SOCS1 and IκBβ) might indeed be involved in the expression and functioning of the AMPA receptors.

The majority of fast excitatory neurotransmission in the brain occurs at glutamatergic synapses. The extensive dendritic arborisations of pyramidal neurons in the neocortex and hippocampus harbor thousands of synaptic connections, each formed on tiny protrusions called dendritic spines. Spine synapses are rapidly established during early postnatal development – a key period in neural circuit assembly – and are subject to dynamic activity-dependent plasticity mechanisms that are believed to underlie neural information storage and processing for learning and memory. Recent decades have seen remarkable progress in identifying diverse plasticity mechanisms responsible for regulating synapse structure and function, and in understanding the processes underlying computation of synaptic inputs in the dendrites of individual neurons. These advances have strengthened our understanding of the biological mechanisms underlying brain function but, not surprisingly, they have also raised many new questions. Using a combination of whole-cell electrophysiology, 2-photon imaging and glutamate uncaging in rodent brain slice preparations, I have helped to document the subtype-specific regulation of glutamate receptors during a homeostatic form of synaptic plasticity at CA1 pyramidal neurons of the hippocampus, and have discovered novel synaptic calcium dynamics during a critical period of neural circuit formation. First, we found that during a homeostatic response to prolonged inactivity, both AMPA and NMDA subtypes of glutamate receptors undergo a switch in subunit composition at synapses, but exhibit a divergence in their subcellular localization at extrasynaptic regions of the plasma membrane (this work was published in the Journal of Neuroscience in 2013). In separate series of experiments using 2-photon calcium imaging, I discovered a functional coupling between NMDA receptor activation and intracellular calcium release at dendritic spines and dendrites that is selectively expressed during a critical period of synapse formation. This synaptic calcium signaling mechanism enabled the transformation of distinct spatiotemporal patterns of synaptic input into salient biochemical signals, and is thus apt to locally regulate synapse development along individual dendritic branches. Consistent with this hypothesis, I found evidence for non-random clustering of synapse development between neighboring dendritic spines. Together, these experimental results expand the current understanding of the dynamics of synapse function during homeostatic plasticity and early postnatal development. --- Les synapses glutamatergiques soutiennent la majorité de la neurotransmission excitatrice rapide du cerveau. Des milliers de ces synapses, localisées sur de minuscules saillies appelées épines dendritiques, décorent les vastes arborisations dendritiques des neurones pyramidaux du néocortex et de l'hippocampe. Ces synapses sont formées tôt lors du développement postnatal et sont soumises à des mécanismes dynamiques de plasticité qui sous-tendent, croit-on, les capacités d'apprentissage et de mémoire du cerveau. Les dernières décennies ont vu des progrès remarquables dans l'identification de divers mécanismes de régulation de la structure et de la fonction des synapses sur différentes échelles de temps, et dans la compréhension des processus qui régissent l’intégration des inputs synaptiques au niveau des dendrites individuelles. Ces progrès ont renforcé notre compréhension des éléments fondamentaux régissant la fonction cérébrale et ont ouvert de nouvelles voies d’investigations neurophysiologiques. En utilisant une combinaison d’électrophysiologie cellulaire, d'imagerie à deux-photons et de photolibération de glutamate sur des neurones pyramidaux de la région CA1 de l'hippocampe de rats, j’ai contribué à la découverte et à la caractérisation de nouvelles régulations des récepteurs du glutamate durant la plasticité synaptique homéostatique. J’ai également découvert un nouveau type de dynamique de calcium synaptique relié à une organisation spatiale du développement des synapses pendant une période critique de l’ontogénie des circuits neuronaux. Dans la première étude, nous avons constaté que lors d'une plasticité de type homéostatique induite par une inactivité prolongée, les récepteurs de glutamate de types AMPA et NMDA sont soumis à un changement important dans la composition de leurs sous-unités. De plus, nous avons observé un ciblage différentiel de ces récepteurs vers des compartiments subcellulaires spécifiques des neurones. Dans une série d'expériences séparée utilisant l’imagerie calcique à deux-photons, j’ai découvert un couplage fonctionnel durant le développent entre l'activation des récepteurs NMDA et une libération de calcium intracellulaire qui envahit tant les épines dendritiques que les dendrites. J’ai également trouvé que ce mécanisme de signalisation de calcium synaptique transforme des motifs spatiotemporels d’activités synaptiques spécifiques en signaux biochimiques post-synaptiques de manière à potentiellement réguler l’organisation spatiale des synapses durant le développement. Conformément à cette hypothèse, j’ai observé des manifestations fonctionnelles claires de regroupement dans l’espace de synapses de forces similaires le long de branches dendritiques individuelles. Ensemble, ces résultats expérimentaux élargissent notre compréhension actuelle de de la fonction des synapses durant la plasticité homéostatique ainsi que durant le développement postnatal du cerveau. En étudiant les mécanismes neurophysiologiques de base, il sera possible d'avoir un aperçu plus profond du fonctionnement du cerveau et de ses pathologies.

A holy grail in neuroscience is being able to control plasticity to facilitate recovery from insult in the adult brain. Despite success in animal models, few therapies have translated from bench to bedside. This thesis is aimed at addressing 2 major stumbling blocks in translation. The first gap is in our understanding of the mechanisms of plasticity-enhancing therapies, and the second is in our understanding the relevance of those mechanisms for human development. In chapters 2 and 3, I address the first gap by asking whether fluoxetine, a selective serotonin reuptake inhibitor, which reinstates juvenile-like plasticity in adult animals, reinstates a juvenile-like synaptic environment. We found evidence to suggest that fluoxetine is neuroprotective, as it rescued all of the MD-driven changes, but surprisingly we found no evidence that fluoxetine recreated a juvenile-like synaptic environment, with the exception of Ube3A. Ube3A is necessary for critical period plasticity, indicating that Ube3A may play a crucial in enhancing plasticity in the adult cortex. In chapter 4, I address whether D-serine, an amino acid that has similar effects to fluoxetine in terms of both plasticity and anti-depression, shares a common neurobiological signature with fluoxetine. I found that D-serine’s effects were strikingly similar to fluoxetine, with respect to markers of the E/I balance, indicating that it may be an effective alternative to fluoxetine. In chapter 5, I address the second gap by studying the development of 5 glutamatergic proteins in human V1. Some changes occurred early, as would be predicted from animals studies, while other changes were protracted, lasting into the 4th decade. These results will help guide the use of treatments, like fluoxetine, which effect glutamatergic proteins. iv Together the findings in this thesis significantly advances our understanding of the mechanisms involved in restating plasticity in the adult cortex, and their relevance to humans. / Dissertation / Doctor of Philosophy (PhD) / Neurons change to rewire, adapt, and recover. This plasticity is greatest early in development, so much research has focused on bringing it back in adults. There has been amazing progress in animal models, but this has not translated to humans. Two reasons for this are that we do not fully understand the mechanisms of these treatments in animals or whether those mechanisms are relevant for humans. My thesis addresses this by studying how 2 treatments, fluoxetine and D-serine, affect proteins that are important for plasticity, and how those proteins develop in the humans. I found that these treatments are neuroprotective, but do not recreate a younger state. One interesting standout is an increase in Ube3A, which is essential for juvenile plasticity. I also found that much of human development is similar to animals, but the time course for some proteins is uniquely prolonged in humans. These findings have implications for the use of plasticity-enhancing treatments at different ages.

No description available.

Yes / Neuronal activity regulates the transcription and translation of the immediate-early gene Arc/Arg3.1, a key mediator of synaptic plasticity. Proteasomedependent degradation of Arc tightly limits its temporal expression, yet the significance of this regulation remains unknown. We disrupted the temporal control of Arc degradation by creating an Arc knockin mouse (ArcKR) where the predominant Arc ubiquitination sites were mutated. ArcKR mice had intact spatial learning but showed specific deficits in selecting an optimal strategy during reversal learning. This cognitive inflexibility was coupled to changes in Arc mRNA and protein expression resulting in a reduced threshold to induce mGluR-LTD and enhanced mGluR-LTD amplitude. These findings show that the abnormal persistence of Arc protein limits the dynamic range of Arc signaling pathways specifically during reversal learning. Our work illuminates how the precise temporal control of activity-dependent molecules, such as Arc, regulates synaptic plasticity and is crucial for cognition. / Open access funded by Biotechnology and Biological Sciences Research Council

No description available.

Die kortikale spreading depression (SD), wie sie von Leão 1944 zuerst beschrieben wurde, ist ein elektrophysiologisches Phänomen, das in der Pathophysiologie der Aurasymptomatik einer Mi-gräneattacke und Ischämie-induzierter Zellschäden diskutiert wird. Während der akuten fokalen zerebralen Ischämie treten eine Reihe von Ereignissen wie eine massive Entzündungsreaktion und die allmähliche Einbeziehung einer zunächst viablen ischämischen Randzone - der Penum-bra - in das infarzierte Hirngewebe auf. Da an diesen Ereignissen SD-ähnliche Depolarisationen kausal beteiligt sind, ist die pharmakologische Verringerung von SD-Episoden bzw. eine Ver-kleinerung ihrer Amplitude und Dauer unter in vitro als auch tierexperimentellen in vivo Bedin-gungen eine mögliche neuroprotektive Strategie. In der vorliegenden Arbeit wurde ein in vitro Modell beschrieben, das am Hirnschnittpräparat des Neokortex der adulten Ratte eine reproduzierbare Auslösung von SD-Wellen unter normoxi-schen Bedingungen gestattet. Anhand von charakteristischen elektrophysiologischen Parametern einer SD wie Amplitude, Dauer und Ausbreitungsgeschwindigkeit wurden die gute Überein-stimmungen dieses in vitro Modells mit in vivo Modellen gezeigt. Obwohl SD Wellen am nicht-ischämischen Kortex keine morphologischen Schäden verursachen, zeigte sich in den hier vorge-stellten Experimenten eine funktionelle Unterdrückung der GABAergen hemmenden Mechanis-men des Neokortex nach repetitiven SDs auch bei ausreichender Energie- und Sauerstoffversor-gung. Die hier diskutierten Ergebnisse demonstrierten, daß unter in vitro Bedingungen der AMPA-Glutamatrezeptor für die Auslösung und Ausbreitung einer SD eine untergeordnete Rolle spielt. Demgegenüber erwies sich die NMDA-Rezeptoraktivierung als herausragend für eine SD, da die Blockade dieses Rezeptors mit dem nicht-kompetitiven Antagonisten Ketamin die SD-Amplitude und SD-Dauer signifikant verringerte. Die Anwendung der selektiven 5-HT1A-Agonisten 8-OH-DPAT und BAY x 3702 erwies sich als eine neue Möglichkeit, die Zeitdauer einer SD zu verringern. Die aufgezeigte SD-induzierte neuronale Hyperexzitabilität kann unter normoxischen Bedingun-gen zelluläre Dysfunktionen verursachen und auch an einer Generierung der Aura eines Migrä-neanfalls beteiligt sein. Unter hypoxisch-ischämischen Bedingungen könnte eine SD-induzierte Dysfunktion GABAerger Kontrollmechanismen die Ausweitung ischämischer Zellschäden be-wirken. Die Hoffnungen auf eine effektive Schlaganfalltherapie haben sich mit den bisherigen NMDA-Antagonisten trotz ihrer hier bestätigten guten in vitro Wirksamkeit aufgrund der Interferenz mit physiologischen Glutamatfunktionen im Kortex nicht erfüllt. Die hier gezeigte konzentrationsab-hängige Verkürzung der SD-Dauer durch die Aktivierung des 5-HT1A-Serotoninrezeptors unter in vitro Bedingungen kann bei der bekannten hohen 5-HT1A-Rezeptor-mRNA-dichte an beson-ders ischämievulnerablen Neuronen einen neuen neuroprotektiven Ansatz auch beim Menschen darstellen. Weitere Untersuchungen müssen zeigen, ob die hier beschriebene enge Verflechtung des serotonergen Systems mit der glutamatergen Neurotransmission eventuell auch zu uner-wünschte Wirkungen unter in vivo Bedingungen führt. / Repetitive cortical spreading depression (SD) and SD-like events, associated with a massive de-polarization of neuronal and glial cells, is thought to play a key role in the induction of neuronal damage in the peri-infarct zone following experimental focal cerebral ischemia. In addition, ex-perimental and clinical data suggest that SD is the underlying mechanism of neurological distur-bances during migraine auras as well. However, detailed analyses on the consequences of repeti-tive SDs on cortical function and involved receptors are lacking. Using an in vitro rat model of SD I investigated in this thesis the electrophysiological properties of repetitive potassium chloride (KCl)-induced SDs, their influence on synaptic neurotransmis-sion and the effects of ionotropic glutamate antagonists and 5-HT1A agonists in neocortical slices obtained from adult rats. Whereas repetitive SDs revealed only non-significant variations in du-ration, amplitude and integral when elicited at intervals of 30 min, paired-pulse inhibition of ex-tracellularly recorded field potential responses was significantly affected by repetitive SD even under normoxic conditions. Compared to the control recordings, each SD episode caused a sig-nificant decrease in the efficacy of intracortical GABAergic inhibition by approximately 10%. Since excitatory synaptic transmission was unaffected, these data indicate that repetitive SDs cause a selective suppression of GABAergic function even in the non-ischemic brain. None of the compounds tested prevented the SD-induced cortical disinhibition. However, the SD-associated negative shift in the extracellular DC potential was reduced by ketamine, a selective N-methyl-D-aspartic acid (NMDA-) receptor antagonist. Ketamine significantly (p < 0.01) re-duced the amplitude of the first SD peak and blocked the second SD peak. Ketamine also de-creased the SD duration at half maximal amplitude (p < 0.05). NBQX, a selective a-amino-3- hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist did not affect the SD-accompanied cortical depolarization, whereas selective 5-hydroxytryptamine (5-HT)1A receptor agonists 8-OH-DPAT and BAY x 3702 shortened concentration-dependently the duration of the SD up to 50 %. Nevertheless, both 5-HT1A receptor agonists caused a strong disinhibition of neu-ronal function with a tendency towards paired-pulse facilitation as well. Thus, repetitive SD and SD-like events may induce neuronal hyperexcitability due to a selective suppression of intrinsic inhibitory GABAergic function. Under normoxic conditions, SD-induced disinhibition may be involved in the generation and maintenance of migraine or associated neurological disturbances. Under hypoxic-ischemic conditions, neuronal hyperexcitability may contribute to the gradual expansion of the ischemic core and the metabolic deterioration of the penumbral tissue after SD episodes. This underlines the deleterious effect of SD to the outcome of focal cerebral ischemia. Although the precise mecha-nisms of SD generation and propagation remains far from established, the present pharmacologi-cal profile of KCl-induced SD in vitro links the induction and propagation of SD in rat neocorti-cal slices mainly to a local increase of [K + ] e and a subsequent activation of NMDA- receptors. This corroborates the neuroprotective effect of a NMDA- receptor blockade observed in various in vitro and in vivo models. However, as it has been demonstrated in clinical trials, NMDA- re-ceptor antagonists in use today cause psychomimetic and cardiovascular side effects in humans and are therefore currently of low clinical benefit. The activation of 5-HT1A receptors by selective agonists represents a new pharmacological strategy in the treatment of acute ischemic stroke, since shortened SD waves may represent a less energy-consuming process under conditions of limited energy supply and are probably associated with an efflux of excitatory neurotransmitters to a lesser extent. The potential clinical benefit of 5-HT 1A receptor agonists remains to be investi-gated in clinical trials, since systemic administration of these compounds after the onset of acute focal cerebral ischemia might interfere with normal functions of glutamatergic neurotransmission in the intact, non-ischemic brain.

Made available in DSpace on 2015-04-14T13:34:40Z (GMT). No. of bitstreams: 1 409596.pdf: 723209 bytes, checksum: caf0c117dfa3ea5f2b501cc60cc59052 (MD5) Previous issue date: 2008-10-14 / Introdu??o: A mem?ria ? aquisi??o, consolida??o e evoca??o de informa??es. Envolve sempre um componente emocional, que se acrescenta ?s informa??es de ?ndole cognitiva. Quando a mem?ria ? conseq??ncia de uma situa??o estressante e traum?tica, envolve emo??es dessa ?ndole e se estabelece atrav?s da am?dala e do hipocampo, sendo mais resistentes ? extin??o e ao esquecimento. A ansiedade e o estresse influenciam a fase inicial da consolida??o da mem?ria, atrav?s de v?rias vias modulat?rias, cujo efeito se incorpora ao restante do conte?do de cada mem?ria. No caso de estresse particularmente intenso, h? tend?ncia ? evoca??o reiterada da mem?ria traum?tica, provocando uma esquiva persistente a qualquer est?mulo que seja associado ? mesma. O TOP ? um medicamento eficaz na epilepsia, que tem entre seus efeitos colaterais, que s?o concentra??o dependente, a diminui??o da mem?ria de trabalho e da flu?ncia verbal, provocando confus?o e torpor. Materiais, m?todos e hip?teses avaliadas: Foi avaliada a a??o do TOP (10mg/kg) na consolida??o e extin??o da mem?ria de longa dura??o em 84 ratos Wistar, divididos em 6 grupos caso e um grupo controle. A a??o do TOP sobre a consolida??o foi avaliada por sua administra??o imediatamente ap?s, ou 3 horas ap?s o treino. Na avalia??o da extin??o, o TOP foi administrado por 14 dias antes, ou 5 dias durante a extin??o. Em todos os experimentos os animais iniciaram os testes 15 dias ap?s o treino. O treino consistiu em medir o tempo de lat?ncia para descer da plataforma no paradigma de esquiva inibit?ria, momento em que receberam um choque de 1 mA por 2 segundos. A a??o do TOP sobre a consolida??o e extin??o foi avaliada em testes repetidos, sem o choque, em que se mediu a lat?ncia de descida da plataforma nos tempos T1 a T5 e no teste final T6, 48 horas ap?s. Foi realizada tamb?m uma contra prova para avaliar se havia a??o direta do TOP na perda da mem?ria quando administrado por 5 dias sem passar pelo procedimento de extin??o. Resultados: O TOP administrado p?s-treino interferiu com a consolida??o da mem?ria. O resultado foi mais eficaz quando administrado 3 h ap?s o treino. O TOP n?o induziu a extin??o da mem?ria quando administrado antes da extin??o por 14 dias, por?m a facilitou quando administrado por 5 dias durante a mesma. O TOP administrado por uma semana, sem passar pelo procedimento de extin??o, n?o provocou a perda da mem?ria. Sugest?o: O TOP talvez possa ser um medicamento que auxilie pacientes com estresse p?s-traum?tico, assim como aqueles considerados borderline, que apresentam um comportamento autodestrutivo relacionado a traumas na inf?ncia.