Conselho Nacional de Desenvolvimento Científico e Tecnológico / In Alzheimer s disease (AD), β-amyloid peptide (Aβ) has been linked with synaptic loss and cognitive dysfunction, albeit the precise mechanism remains unknown. An involvement of N-Methyl-D-Aspartate receptors (NMDAR) in AD is proposed, since its inhibition attenuates some aspects of AD s neuropathology. In this regard, polyamines, like spermidine and spermine, positive modulators of NMDARs, have been shown to have both concentration and synthesis increased by Aβ. Using the novel object recognition task we showed that negative modulation of polyamine system, been trough blockade of its binding site at NMDAR by arcaine (0.02 nmol/site), traxoprodil (0.002 nmol/site), or inhibition of polyamine synthesis by DFMO (2.7 nmol/site), reverses Aβ25-35-induced memory impairment in mice. The activation of polyamine binding site at NMDAR located at extrasynaptic sites might underlie the cognitive deficits of Aβ25-35-treated mice, since incubation of hippocampal neuron cultures with spermidine (400 μM) or Aβ25-35 (10 μM) significantly increased nuclear accumulation of jacob protein, a marker of extrasynaptic NMDAR activation. Moreover, traxoprodil (4nM), arcaine (4 μM) or DFMO (5 μM) blocked the Aβ-induced jacob nuclear translocation. Activation of extrasynaptic NMDAR in neurons leads to striping of synaptic contacts and simplification of neuronal cytoarchitecture. Incubation of hippocampal neuron cultures with traxoprodil (4 Nm), arcaine (4 μM) or DFMO (5 μM) reversed the deleterious effects of Aβ25-35 on dendritic spine number and spine morphology. We also evaluated the involvement of A-type K+ currents on the Aβ25-35-induced memory impairment. Administration of Tx3-1 (3 100 pmol/site), a selective IA blocker, restored memory of mice injected with Aβ25-35 and tested on the novel object recognition task The reversal of memory impairment and the protective effect on dendritic spine alterations exerted by the modulators of the polyamine system suggest the polyamine binding site at extrasynaptic NMDAR a potential player in Aβ-induced cognitive deficit. / O peptídeo β-amiloide (Aβ), reconhecido como agente tóxico na Doença de Alzheimer (DA) é implicado como causador de danos cognitivos e sinápticos, apesar de os mecanismos não serem completamente compreendidos. O envolvimento do receptor N-metil-D-aspartato (NMDA) na DA é sugerido, visto que o seu bloqueio atenua alguns aspectos neuropatológicos da DA. Nesse contexto, tem sido demonstrado que as poliaminas, como espermidina e espermina, moduladores positivos do receptor NMDA, possuem níveis e síntese elevada tanto no cérebro de pacientes com DA como em preparações in vitro utilizando o peptídeo Aβ. Neste estudo demonstrou-se que a modulação do sistema das poliaminas, através do bloqueio do seu sítio de ligação no receptor NMDA por arcaína (0,02 nmol/sítio), traxoprodil (0,002 nmol/sítio) ou da inibição de sua síntese por DFMO (2,7 nmol/sítio), reverte o déficit cognitivo induzido pela injeção de Aβ25-35 em camundongos testados na tarefa de reconhecimento de objetos. A ativação do sítio de ligação das poliaminas em receptores NMDA extrassinápticos pode subjazer o déficit cognitivo de camundongos injetados com Aβ25-35, visto que a incubação de culturas primárias de neurônios hipocampais com espermidina (400 μM), NMDA (200 μM) ou Aβ25-35 (10 μM) aumenta o acúmulo nuclear de jacob, um marcador de ativação de receptores NMDA extrassinápticos, de maneira significante. Ademais, traxoprodil (4 nM), arcaína (4 μM) ou DFMO (5 μM) bloquearam o acúmulo nuclear de jacob induzido por Aβ. A ativação de receptores NMDA extrassinápticos em neurônios leva a simplificação da citoarquitetura neuronal e a diminuição de contatos sinápticos. Aqui demonstrou-se que a incubação de culturas de neurônios hipocampais com traxoprodil (4 nM), arcaína (4 μM) ou DFMO (5 μM) reverte as alterações na a densidade e morfologia de espinhas dendríticas induzido pela incubação com Aβ25-35. Ainda, também avaliou-se o envolvimento de correntes de K+ do tipo A no déficit cognitivo induzido pela injeção i.c.v. de Aβ25-35. A administração de Tx3-1 (3 100 pmol/sítio), um bloqueador seletivo de correntes IA, reverteu o prejuízo de memória de camundongos injetados com Aβ25-35 e testados na tarefa de reconhecimento de objetos. A reversão dos danos cognitivos e sinápticos induzidos por Aβ25-35 através da modulação do sistema das poliaminas sugere a estimulação do sítio de ligação das poliaminas no receptor NMDA, possivelmente extrassínaptico, como um dos mecanimos por trás do déficit cognitivo induzido pelo peptídeo Aβ.

No description available.

Made available in DSpace on 2014-12-17T15:16:04Z (GMT). No. of bitstreams: 1 AnaCLN.pdf: 1365991 bytes, checksum: a91aa932e949e0fb6e624f6ad5057083 (MD5) Previous issue date: 2009-07-02 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The locomotion is one of the most important capabilities developed by the animals, whose improvement is dependent on several neural centers, including the spinal cord. This activity promotes a lot of spinal modifications that enable it to adapt and improve their connections. This study aimed to observe the morphological changes occurring in the spinal cord after locomotor training in intact rats. For that we used male Wistar rats, which were submitted to locomotor training in wheel activity in protocols 1, 3 and 7 days (30min/day), and the results were compared to a control group not subjected to exercise. Coronal sections of 40 μm of the lumbosacral spinal cord were subjected to immunohistochemical techniques anti-Egr1, anti-NMDA and anti-SP, to characterize the spinal plasticity related to these substances. Egr1-immunoreactive cells were increased in all laminas, essentially in those more intensely activated by locomotion, laminas IV-X levels L4-S3. All observed sections expressed NMDA-immunoreactivity. Analysis of SP in the spinal dorsal horn resulted no significant variations of this neuropeptide related to locomotion. The results suggest that locomotor training provides synaptic plasticity similar to LTP in all laminas of the lumbosacral spinal cord, in different intensities. However, the SP appears do not participate of this process in the spinal dorsal horn. This work will contribute for consolidating and characterization of synaptic plasticity in the spinal cord / A locomo??o ? uma das mais importantes capacidades desenvolvidas pelos animais, cujo aperfei?oamento ? dependente de v?rios centros neurais, incluindo a medula espinal. Esta atividade promove v?rias modifica??es espinais que a possibilita se adaptar e aperfei?oar suas conex?es. Este trabalho teve por objetivo observar as altera??es morfol?gicas ocorridas na medula espinal ap?s o treinamento locomotor de ratos intactos. Para isso foram utilizados ratos Wistar machos, os quais foram submetidos ao treinamento locomotor na roda de atividade em protocolos de 1, 3 e 7 dias (30min/dia), e os resultados foram comparados aos de um grupo controle, n?o submetido ao exerc?cio. Cortes coronais de 40 μm da medula espinal lombossacral foram submetidos a t?cnicas imunohistoquimicas anti-Egr1, anti-NMDA e anti-SP, para caracterizarmos a plasticidade espinal quanto a essas subst?ncias. C?lulas imunorreativas a Egr1 estavam aumentadas em todas as l?minas, intensamente nas regi?es mais ativadas pela locomo??o, l?minas IV-X dos n?veis L4-S3. Todas as sec??es observadas expressaram imunorreatividade a NMDA. A an?lise da SP no corno dorsal espinal resultou em aus?ncia de varia??es significantes deste neuropept?deo relacionadas com a locomo??o. Diante dos resultados, sugerimos que o treinamento locomotor proporciona plasticidade sin?ptica semelhante a LTP em todas as l?minas da medula espinal, em intensidades diferenciadas. No entanto, esse processo parece n?o ter a participa??o da SP no corno dorsal espinal. Este trabalho vem contribuir para a consolida??o e caracteriza??o da plasticidade sin?ptica na medula espinal

Initialement encodés dans l’hippocampe, les nouveaux souvenirs déclaratifs deviennent progressivement dépendants d’un réseau distribué de neurones corticaux au cours de leur maturation dans le temps. Cependant, les mécanismes cellulaires et moléculaires sous-­‐tendant la consolidation et le stockage à long terme de ces nouveaux souvenirs au sein des réseaux corticaux restent à élucider. Les récepteurs N-­‐méthyl-­‐D-­‐aspartate (RNMDA) jouent un rôle essentiel dans l’induction et la régulation des changements synaptiques sous-­‐tendant les processus mnésiques de type associatifs. Sur la base de leurs propriétés biophysiques respectives, nous avons formulé l’hypothèse que la redistribution synaptique des deux formes principales de sous-­‐unités GluN2 exprimées dans le néocortex adulte (GluN2A and GluN2B), pourrait constituer un mécanisme de régulation de la plasticité synaptique supportant l’intégration et la stabilisation progressive des souvenirs au niveau cortical au cours du processus de consolidation mnésique. En combinant, chez le rat adulte, une approche comportementale, biochimique, pharmacologique et des stratégies innovantes consistant à manipuler le trafic de sous-­‐unités des RNMDA à la surface synaptique, nos résultats mettent en évidence un changement cortical dans la composition synaptique en sous unités GluN2, lequel régule la stabilisation progressive de la mémoire à long terme au sein des réseaux corticaux. Nous avons d'abord établi que les RNMDA contenant la sous-­‐unité GluN2B, via leur interaction spécifique avec une protéine clé de la signalisation synaptique, la CaMKII, sont préférentiellement recrutés lors de la phase d’encodage pour permettre l’allocation des nouveaux souvenirs olfactifs associatifs dans un réseau de neurones corticaux spécifique. Au cours du processus de consolidation, nous avons révélé que la redistribution des RNMDA corticaux contenant les sous-­‐unités GluN2B vers l’extérieur ou l’intérieur de l’espace synaptique suite à l’apprentissage, contrôle respectivement la stabilisation de la mémoire à long terme et son oubli au cours du temps. Enfin, renforcer l’acquisition initiale conduit à une augmentation plus rapide du ratio post-­‐synaptique GluN2A/GluN2B et accélère la cinétique du dialogue hippocampo-­‐cortical, ce qui se traduit par une stabilisation accélérée des souvenirs au sein des réseaux corticaux. Pris dans leur ensemble, nos travaux montrent que le trafic des GluN2B-­‐RNMDA corticaux représente un mécanisme cellulaire majeur conditionnant le devenir des traces mnésiques (i.e. stabilisation versus oubli) et apporte un éclairage nouveau sur la façon dont le cerveau organise les souvenirs récents et anciens. / Initially encoded in the hippocampus, new declarative memories are thought to become progressively dependent on a broadly distributed cortical network as they mature and consolidate over time. Although we have a good understanding of the mechanisms underlying the formation of new memories in the hippocampus, little is known about the cellular and molecular mechanisms by which recently acquired information is transformed into remote memories at the cortical level. The N-­‐methyl-­‐D-­‐aspartate receptor (NMDAR) is widely known to be a key player in many aspects of long-­‐term experience-­‐dependent synaptic changes underlying associative memory processes. Based on their distinct biophysical properties, we postulated that the activity-­‐dependent surface dynamics of the two predominant GluN2 subunits (GluN2A and GluN2B) of NMDARs present in the adult neocortex could provide a metaplastic control of synaptic plasticity supporting the progressive embedding and stabilization of long-­‐lasting associative memories within cortical networks during memory consolidation. By combining, in adult rats, behavioral, biochemical, pharmacological and innovative strategies consisting in manipulating trafficking of NMDAR subunits at the cell membrane, our results identify a cortical switch in the synaptic GluN2-­‐containing NMDAR composition which drives the progressive embedding and stabilization of long-­‐lasting memories within cortical networks. We first established that cortical GluN2B-­‐containing NMDARs and their specific interactions with the synaptic signaling CaMKII protein are preferentially recruited upon encoding of associative olfactory memories to enable neuronal allocation, the process via which a new memory trace is thought to be allocated to a given neuronal network. As these memories are progressively processed and embedded into cortical networks, we observed a learning-­‐induced surface redistribution of cortical GluN2B-­‐containing NMDARs outwards or inwards synapses which respectively drives the progressive stabilization and subsequent forgetting of remote memories over time. Finally, increasing the strength, upon encoding, of the initial memory leads to a faster increase of the cortical GluN2A/GluN2B synaptic ratio and accelerates the kinetics of hippocampal-­‐cortical interactions, which translated into a faster stabilization of memories within cortical networks. Taken together, our results provide evidence that GluN2B-­‐NMDAR surface trafficking controls the fate of remote memories (i.e. stabilization versus forgetting), shedding light on a novel mechanism used by the brain to organize recent and remote memories.

Le récepteur du glutamate de type N-méthyl-D-aspartate (NMDAR) est un transducteur clef dans la physiologie du système nerveux et dans nombre de ses pathologies, selon qu’il est localisé à la synapse ou en position extra-synaptique respectivement. Son activité est sous le contrôle étroit du ‘site-glycine’, dont l’activation est gouvernée par la disponibilité en coagoniste. Pourtant, on ignore encore largement les règles qui régissent cette étape limitante de l’activation des NMDARs in situ. Par ailleurs, l’ensemble des onnaissances actuelles suggère que les astrocytes pourraient contrôler les NMDARs dans le contexte des interactions entre cellules gliales et neurones, en particulier via la libération du gliotransmetteur D-sérine. Le principal objectif de ce travail de thèse a été de comprendre les modalités du contrôle endogène des NMDARs par leur site co-agoniste, dans la région CA1 de l’hippocampe. Nous avons porté notre attention, avant tout, sur les acteurs de ce contrôle : la glycine et la D-sérine, qui sont les ligands endogènes du site-co-agoniste. Nous nous sommes intéressés à leur contribution respective dans le contrôle des NMDARs, aux dynamiques de ce contrôle en fonction de l’activité neuronale, à ses variations en fonction de la localisation des NMDARs, ainsi qu’à ses modifications développementales. Nous montrons par des approches d’électrophysiologie que la D-sérine, et non la glycine, est le co-agoniste endogène des NMDARs à la synapse CA3-CA1 chez l’adulte. Elle est délivrée par les prolongements astrocytaires environnants, d’une manière qui est influencée par l’activité synaptique. Sa libération répond à un mécanisme vésiculaire et est dépendante de la signalisation calcique intra-astrocytaire. De cette manière, les astrocytes exercent un contrôle étroit et dynamique des NMDARs à l’état basal et au cours de phénomènes de plasticité synaptique. En contre partie, à l’inverse de leurs homologues localisés à la synapse, les NMDARs extrasynaptiques sont contrôlés par la glycine à l’âge adulte. Cette compartimentation spatiale est dictée par une disponibilité différentielle des deux co-agonistes aux différents sites. Elle est également favorisée par une composition en sous-unités des NMDARs synaptiques et extra-synaptiques différente qui leur confère une affinité distincte pour la glycine et la D-sérine. Enfin, le contrôle des NMDARs par la D-sérine astrocytaire observé à l’âge adulte n’est pas opérationnel à la naissance. En effet, il ne se met en place qu’au cours du premier mois post-natal, de façon concomitante au changement de composition en sous-unités des NMDARs. / N-methyl D-aspartate receptors (NMDARs) are central to many aspects of brain physiology and pathology, which they impact differently depending on their synaptic or extrasynaptic location, respectively. In addition to glutamate, they are gated by the necessary binding of a co-agonist on the so-called ‘glycine-binding site’. However, very little is known about the rules that govern the control of NMDARs through this site, in situ. Evidence now suggests that astrocytes could play a critical role in controlling NMDARs activity, in particular through the release of the gliotransmitter D-serine. In the present work, we aimed at understanding how NMDARs are endogenously controlled through their co-agonist binding site, in the CA1 region of rat hippocampus. We primarily focused on the role of two endogenous ligands of this site: glycine and D-serine. We investigated their relative contribution in the control of NMDARs at the different subcellular locations, the dynamics of such control according to synaptic activity, as well as possible changes during post-natal development. Using elecrophysiological approaches, we demonstrate that NMDARs are gated by Dserine, but not glycine, at CA3-CA1 synapses in adults. D-serine is supplied at least in part by surrounding astrocytes in an activity-dependant manner. Its release occurs in response to calcium signalling within the astrocyte and in a vesicular way. Correspondingly, we found astrocytic supply of D-serine to be essential for NMDARs-dependant functions such as synaptic plasticity. In contrast with their synaptic counterparts, extrasynaptic NMDARs are gated by endogenous glycine and not by D-serine. We provide evidence that this compartmentation relies on the differential availability of the two co-agonists at synaptic and extrasynaptic sites. Besides, due to differences in their subunit composition, synaptic and extrasynaptic NMDARs may have preferential affinity for D-serine and glycine respectively. Finally, we show that the control of the NMDAR co-agonist site is developmentally regulated. Early after birth, glycine is the endogenous co-agonist of synaptic NMDARs. The control exerted by D-serine only progressively appears during the first post-natal month, as the switch in NMDARs subunit composition occurs, suggesting a maturation of cellular interactions at the tripartite synapse.

<p>Obsessive-compulsive disorder (OCD) is a devastating illness that afflicts around 2% of the world's population with recurrent distressing thoughts (obsessions) and repetitive ritualistic behaviors (compulsions). While dysfunction at excitatory glutaminergic excitatory synapses leading to hyperactivity of the orbitofrontal cortex and head of the caudate - brain regions involved in reinforcement learning - are implicated in the pathology of OCD, clinical studies involving patients are unable to dissect the molecular mechanisms underlying this cortico-striatal circuitry defect. Since OCD is highly heritable, recent studies using mutant mouse models have shed light on the cellular pathology mediating OCD symptoms. These studies point toward a crucial role for deltaFosB, a persistent transcription factor that accumulates with chronic neuronal activity and is involved in various diseases of the striatum. Furthermore, elevated deltaFosB levels results in the transcriptional upregulation of Grin2b, which codes GluN2B, an N-methyl-D-aspartate glutamate receptor (NMDAR) subunit required for the formation and maintenance of silent synapses. Taken together, the current evidence indicates that deltaFosB-mediated expression of aberrant silent synapses in caudate medium spiny neurons (MSNs), in particular D1 dopamine-receptor expressing MSNs (D1 MSNs), mediates the defective cortico-striatal synaptic transmission that underlies compulsive behavior in OCD.</p> / Dissertation

<p>The neurosteroids constitute a group of powerful hormones synthesized and acting in the central nervous system. They participate in a number of important central processes, such as memory and learning, mood and neuroprotection. Their effects emerge from rapid interactions with membrane bound receptors, such as the N-methyl-D-aspartate (NMDA) receptor, the gamma-amino-butyric acid receptor and the sigma 1 receptor. The mechanisms of action are separate from classical genomic interactions. </p><p>The aims of this thesis were to identify and characterize the molecular mechanisms underlying the effects of nanomolar concentrations of neurosteroids at the NMDA receptor. </p><p>The results show that the neurosteroids pregnenolone sulfate (PS) and pregnanolone sulfate 3α5βS) differently modulate the NMDA receptor, changing the kinetics for the NMDA receptor antagonist ifenprodil, through unique and separate targets at the NR2B subunit. The effects that appear to be temperature independent were further confirmed in a calcium imagining functional assay. A second functional study demonstrated that PS and 3α5βS affect glutamate-stimulated neurite outgrowth in NG108-15 cells. </p><p>Misuse of anabolic androgenic steroids (AAS) has powerful effects on emotional states. Since neurosteroids regulate processes involved in mood it can be hypothesised that AAS can interact with the action of neurosteroids in the brain. However, chronic administration of the AAS nandrolone decanoate did not alter the allosteric effects of PS or 3α5βS at the NMDA receptor, but changed the affinity for PS, 3α5βS and dehydroepiandrosterone sulfate to the sigma 1 receptor. The results also showed that the neurosteroids displace ³H-ifenprodil from the sigma 1 and 2 receptors without directly sharing the binding site for ³H-ifenprodil at the sigma 1 receptor. The decreased affinity for the neurosteroids at the sigma 1 receptor may be involved in the depressive symptoms associated with AAS misuse.</p><p>The NMDA receptor system is deeply involved in neurodegeneration and the NMDA receptor antagonist ifenprodil exert neuroprotective actions. The findings that neurosteroids interact with ifenprodil at the NMDA receptor may be an opportunity to obtain synergistic effects in neuroprotective treatment.</p>

The neurosteroids constitute a group of powerful hormones synthesized and acting in the central nervous system. They participate in a number of important central processes, such as memory and learning, mood and neuroprotection. Their effects emerge from rapid interactions with membrane bound receptors, such as the N-methyl-D-aspartate (NMDA) receptor, the gamma-amino-butyric acid receptor and the sigma 1 receptor. The mechanisms of action are separate from classical genomic interactions. The aims of this thesis were to identify and characterize the molecular mechanisms underlying the effects of nanomolar concentrations of neurosteroids at the NMDA receptor. The results show that the neurosteroids pregnenolone sulfate (PS) and pregnanolone sulfate 3α5βS) differently modulate the NMDA receptor, changing the kinetics for the NMDA receptor antagonist ifenprodil, through unique and separate targets at the NR2B subunit. The effects that appear to be temperature independent were further confirmed in a calcium imagining functional assay. A second functional study demonstrated that PS and 3α5βS affect glutamate-stimulated neurite outgrowth in NG108-15 cells. Misuse of anabolic androgenic steroids (AAS) has powerful effects on emotional states. Since neurosteroids regulate processes involved in mood it can be hypothesised that AAS can interact with the action of neurosteroids in the brain. However, chronic administration of the AAS nandrolone decanoate did not alter the allosteric effects of PS or 3α5βS at the NMDA receptor, but changed the affinity for PS, 3α5βS and dehydroepiandrosterone sulfate to the sigma 1 receptor. The results also showed that the neurosteroids displace 3H-ifenprodil from the sigma 1 and 2 receptors without directly sharing the binding site for 3H-ifenprodil at the sigma 1 receptor. The decreased affinity for the neurosteroids at the sigma 1 receptor may be involved in the depressive symptoms associated with AAS misuse. The NMDA receptor system is deeply involved in neurodegeneration and the NMDA receptor antagonist ifenprodil exert neuroprotective actions. The findings that neurosteroids interact with ifenprodil at the NMDA receptor may be an opportunity to obtain synergistic effects in neuroprotective treatment.

Female reproductive senescence is widespread among mammalian species, but menopause is limited to species with menstrual cycles. While hormonal changes at menopause have profound impacts in the lives of women at middle age, the complex mechanisms underlying this process remain obscure. All three levels of the hypothalamic-pituitary-gonadal (HPG) axis are involved in reproductive aging, and evidence highlights a critical role for the dysregulation of gonadotropin-releasing hormone (GnRH) neurons, the hypothalamic cells that drive reproductive function. To investigate neuroendocrine mechanisms that may initiate and perpetuate reproductive decline at each step in the transition to acyclicity, I utilized an ovarian-intact middle-aged female rat model of natural reproductive senescence. These studies focused on three hypothalamic nuclei that are known to control GnRH activity: the anteroventral periventricular nucleus (AVPV), the site of positive hormone feedback onto GnRH neurons; the arcuate nucleus (ARC), the site of negative feedback; and the median eminence (ME), the site of GnRH release, with the following specific aims: 1) Characterize neuroendocrine gene and protein expression in female rats throughout the natural transition to acyclicity; 2) Determine the effects of chronic N-methyl-D-asparate receptor subunit 2b (NMDAR-NR2b) inhibition in acyclic females; and 3) Examine neuroendocrine gene expression during premature reproductive senescence after perturbation of the HPG axis. The results of these studies identified novel molecular and cellular changes with age and reproductive cycle status in the ARC and ME, two regions that are underappreciated for their roles in reproductive senescence. Surprisingly, few molecular targets were identified in the AVPV, a region that is much better-studied in this context. In the ME and ARC, I found changes in transcription factors and evidence of altered hormone feedback via changes in sex steroid hormone receptors and enzyme expression with reproductive aging. I also discovered decreased expression of genes for the excitatory neuropeptides, kisspeptin and neurokinin B, as well as decreased percentage of kisspeptin immunoreactive cells and their co-expression with estrogen receptor alpha in the ARC. And finally, in the ME, neurotrophic factor expression was changed with age, and the presence and phosphorylation state of the NR2b subunit of the NMDA receptor contributes to a greater inhibitory tone with acyclicity. Together these studies have identified novel pathways, especially in the ARC and ME, that are related to reproductive decline. Furthermore, changes in the hypothalamic neural and glial network of neurotransmitters, neuropeptides, hormone receptors and other transcription factors are likely contributing to altered responses to hormonal feedback and decreased excitatory drive for GnRH release. / text

Η λειτουργική διαφοροποίηση κατά το διαφραγματοκροταφικό άξονα του ιπποκάμπου αφορά και την επιληψία. Χρησιμοποιώντας το μοντέλο ελεύθερο μαγνησίου και δυναμικά πεδίου παρατηρήσαμε πως οι επιληπτόμορφες εκφορτίσεις παρατηρούνταν πιο συχνά, είχαν μεγαλύτερη συχνότητα, διάρκεια και ένταση στις κοιλιακές τομές. Ο ανταγωνιστής των NMDA υποδοχέων AP5 μείωσε τη διάρκεια μόνο στις κοιλιακές τομές. Η προσθήκη του NMDA προκάλεσε εμμένουσες επιληπτόμορφες εκφορτίσεις στο 51% των κοιλιακών και το 9% των ραχιαίων τομών. Προτείνουμε πως οι υποδοχείς NMDA συμμετέχουν στη μεγαλύτερη ευπάθεια του κοιλιακού ιπποκάμπου τόσο στην έκφραση όσο και στη μακρόχρονη διατήρηση των επιληπτόμορφων εκφορτίσεων. Για να μελετήσουμε την επιληπτογένεση με άρση του αδενοσινεργικού τόνου, χρησιμοποιήσαμε πρωτόκολλα εκλεκτικού ή μη αποκλεισμού των αδενοσινεργικών υποδοχέων σε συνθήκες ελεύθερες μαγνησίου και καταγράψαμε αυθόρμητα ή προκλητά δυναμικά πεδίου στη CA3 σε κοιλιακές και ραχιαίες τομές. O αποκλεισμός του Α1 προκάλεσε επιληπτογένεση στο 31,13% των ραχιαίων και στο 52,76% των κοιλιακών τομών (P<0,05). Ο σύγχρονος αποκλεισμός του NMDA υποδοχέα αύξησε τα ποσοστά επιληπτογένεσης και στους δυο πόλους (76,38% στις ραχιαίες τομές vs 80,68% στις κοιλιακές τομές). Αυτή η NMDA-ανεξάρτητη επιληπτογένεση μειώθηκε σημαντικά με την προσθήκη του ανταγωνιστή των Α2 υποδοχέων κυρίως στις ραχιαίες τομές. O αποκλεισμός του Α1 υποδοχέα σε συνθήκες αποκλεισμού των NMDA υποδοχέων προκάλεσε παρόμοια αύξηση της κλίσης του fEPSP στις ραχιαίες τομές και στις κοιλιακές τομές. Ο επιπλέον αποκλεισμός των Α2 υποδοχέων επανέφερε την κλίση του fEPSP στο αρχικό της μέγεθος μόνο στις ραχιαίες τομές. Ο σύγχρονος αποκλεισμός των Α1 και Α2 υποδοχέων προκάλεσε επιληπτογένεση πρακτικά μόνο στις κοιλιακές τομές. H επιληπτογένεση αυτή ήταν μερικώς NMDA-εξαρτώμενη. Επιπλέον ενώ ο αποκλεισμός του Α1 προκάλεσε αύξηση της επιφάνειας της καμπύλης του fEPSP σε συνθήκες ελεύθερες μαγνησίου μόνο στις ραχιαίες τομές (96,15%), ο σύγχρονος αποκλεισμός των Α1 και Α2 υποδοχέων προκάλεσε αύξηση κατά 196,62% στις ραχιαίες τομές και 105,26% στις κοιλιακές τομές. Συμπεραίνουμε πως ο εκλεκτικός ή μη αποκλεισμός των υποδοχέων της αδενοσίνης προκαλεί διαφορετικά είδη επιληπτογένεσης που οφείλονται στις διαφορετικές δράσεις των υποδοχέων της αδενοσίνης και την ικανότητα του κοιλιακού ιπποκάμπου για ΝMDA-εξαρτώμενη επιληπτογένεση Χρησιμοποιώντας δυναμικά πεδίου σε κοιλιακές τομές και δυο μοντέλα επιληπτογένεσης παρατηρήσαμε πως οι σχετιζόμενες με τις επιληπτόμορφες εκφορτίσεις υψίσυχνες ταλαντώσεις και η διεγερτική νευροδιαβίβαση συμμεταβάλονται κατά τη διάρκεια της επιληπτογένεσης Παθολογικές υψίσυχνες ταλαντώσεις παρατηρήθηκαν πάντα στην NMDA-εξαρτημένη αλλά όχι και την NMDA-ανεξάρτητη επιληπτογένεση. Η διάρκεια των υψίσυχνων ταλαντώσεων συσχετίστηκε με τη διάρκεια των μεσοκριτικών εκφορτίσεων μόνο μετά την επαγωγή της επιληπτογένεσης Χρησιμοποιώντας ερεθισμό 100Hz και αυξημένη συγκέντρωση καλίου επάγαμε LTP με ερεθισμό των παράπλευρων κλάδων στη CA3 σε συνθήκες αποκλεισμού των υποδοχέων NMDA. Ο νέος τύπος του NMDA-ανεξάρτητου αυτού LTP παρουσίασε αργή ανάπτυξη στο χρόνο, δε μετέβαλε τη διευκόλυνση με σύζευξη παλμών και δεν επαγόταν με ταυτόχρονο αποκλεισμό των ευαίσθητων στη νιφεδιπίνη διαύλων ασβεστίου. Το μέγεθος του LTP ήταν σημαντικά μεγαλύτερο στις ραχιαίες τομές σε σχέση με τις κοιλιακές. / Functional segregation along the dorso-ventral axis of the hippocampus refers to epilepsy too. Using the model of magnesium-free medium and field recordings, single epileptiform discharges displayed higher incidence, rate, duration and intensity in ventral compared with dorsal rat hippocampal slices. The NMDA receptor antagonist AP5 shortened the discharges in ventral slices only. At 5 and 10μΜ of NMDA application 51% of the ventral but only 9% of the dorsal slices displayed persistent epileptiform discharges. We propose that the NMDA receptors contribute to the higher susceptibility of the ventral hippocampus to expression and long-term maintenance of epileptiform discharges. To study epileptogenesis following withdrawal of adenosinergic tone we used models of selective or non-selective blockade of adenosine receptors in magnesium-free medium and we recorded spontaneous or evoked field potentials in CA3 in dorsal as well as ventral slices. Blockade of A1 resulted in epileptogenesis in 31,13% of dorsal and in 52,76% of ventral slices used (P<0,05). NMDAR blockade increased epileptogenesis scores in both poles (76,38% in dorsal slices vs 80,68% in ventral slices). This NMDAR-dependent epileptogenesis was significantly aborted by blockade of A2R more in dorsal slices. Blockade of A1R under conditions of NMDAR blockade resulted to a similar increase of fEPSP slope in dorsal and ventral slices. The additional blockade of A2R decreased fEPSP slope to its original value in dorsal slices only. Simultaneous blockade of A1 and A2 receptors induced epileptogenesis practically in ventral slices only. This epileptogenesis was partially NMDA-dependent. Futrhermore A1R blockade resulted to an increase of fEPSP area under conditions of magnesium-free medium in dorsal slices only, whereas simultaneous blockade of both A1 and A2 receptors to an increase by 196,62% in dorsal slices and by 105,26% in ventral slices. We conclude that the selective or not blockade of adenosine receptors induces different kinds of epileptogenesis and this can be attributed to the different actions of adenosine receptors and the capability of ventral hippocampus to support NMDA-dependent epileptogenesis Employing field recordings from ventral hippocampal slices and two models of epileptogenesis, we found that HFOs associated with epileptiform bursts and excitatory synaptic transmission were co-modulated during epileptogenesis Pathological HFOs>200Hz were unequivocally present in persistent bursts induced by NMDA receptor-dependent but not NMDA receptor-independent mechanisms. The duration of pathological HFOs associated with persistent bursts but not of HFOs associated with bursts before the establishment of epileptogenesis was linearly and strongly correlated with the duration of bursts. Using 100Hz trains and medium with a higher concentration of potassium cations we induced LTP by stimulating associational/commissural fibers in CA3 region under conditions of NMDA receptor blockade. This new type of NMDAR-independent LTP displayed slow kinetics, did not change paired pulse facilitation and was prevented by simultaneous blockade of nifedipine-sensitive calcium channels. The incidence as well as the amplitude of LTP was greater in dorsal slices compared to ventral ones.