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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

The role of p35/Cdk5 in the developing cerebral cortex

Rakic, Sonja January 2005 (has links)
This thesis has focussed on the role of cyclin-dependent kinase 5 (Cdk5) and its activator, p35, in controlling the proper formation of the cerebral cortex. First, cortical layer formation in p35 mutants was re-examined. Interestingly, the prenatal layer I (LI) seems wider, more cellular, and without a clear border with the cortical plate (CP) in these animals. Second, interneuron arrangement in p35 and Cdk5 mutants was studied. Molecules, such as neuregulins (NRGs), which can bind to ErbB receptors and potentially signal through the p35/Cdk5 pathway, were also examined. Cortical interneurons express Cdk5, but Cdk5 is not active in developing forebrain in p35 mutants. It appears that migration of cortical interneurons from the ganglionic eminence (GE) is a Cdk5-independent process. However, my results have suggested that: (i) radial inward migration of interneurons, from LI into the CP, might be a Cdk5-dependent mechanism (ii) prenatal cortical interneurons and projection neurons do not communicate directly. Intriguingly, ErbB4 is highly expressed on the surface of migrating cortical interneurons. Two intracellular isoforms of the rat ErbB4 exist, with one having a unique tyrosine residue for binding PI3-kinase. I have shown that, although ErbB4 signalling is necessary for migration of cortical interneurons from the GE, this process could occur through a PI3K-independent mechanism. The hypothesis that the ErbB4 receptor signals via the Cdk5 pathway was also tested. I found that: (i) Roscovitine, a Cdk5 specific inhibitor, impairs the neuronal chemotactic response to NRGlp (ii) Cdk5 phosphorylates ErbB4 threonine (1152) in vitro. Third, splitting of the preplate layer (PPL) in p35 mutants was studied. In these animals the PPL splits incompletely, which results in misplaced subplate neurons and reeler-Uke positioning of thalamocortical axons. In summary, my experiments have provided novel information about some signalling molecules, and their receptors, that are involved in the migration of cortical neurons.
42

Spike output and synaptic plasticity in a feed-forward inhibitory microcircuit in the cerebellar cortex

Mittmann, Wolfgang Matthias Oliver January 2006 (has links)
Feed-forward inhibitory circuits are common building blocks in the mammalian brain and lead to excitatory input also activating inhibitory input to a common postsynaptic neuron. Such circuits are important for regulating neuronal excitability and timing of activity in the brain. In this thesis I have explored the mechanisms and consequences of feed-forward inhibition in the rat cerebellar cortex, which is known to be involved in coordination and timing of movement. Voltage clamp recordings from Purkinje cells in cerebellar slices exhibit a biphasic current waveform in response to stimulation of parallel fibres, consisting of an excitatory postsynaptic current (EPSC) followed by an inhibitory postsynaptic current (IPSC). The latency difference between the two components - only 1.4 ms - and the complete block of the biphasic response by glutamate receptor antagonists confirmed the second component as feed forward inhibition (FFI). The rapid onset of FFI shortens EPSPs, which enhances spike precision and limits summation of independent inputs. Next, I showed that the latency of FFI does not change with distance along active parallel fibres. This suggests that desynchronisation of action potentials travelling along the parallel fibres is insufficient to cause feed-forward inhibition to arrive ahead of excitation, a theory previously used to explain the observed lack of 'beams' of active Purkinje cells along the parallel fibres. Instead, it is argued that this may result from spatial or temporal spread of activity in the granule cell layer leading to early arrival of inhibition. Both excitation and inhibition in Purkinje cells are subject to plastic changes induced by climbing fibre activation. In a feed-forward network, what is the net effect of this plasticity on the output of the cerebellar cortex First I showed that both inhibition and excitation undergo long-term depression (LTD) to a similar extent when paired with climbing fibre input. This plasticity was reflected in corresponding changes in Purkinje cell spike output triggered by independent inhibitory and excitatory inputs: parallel fibre LTD reduced, and LTD of inhibition increased the number of spikes evoked by the respective inputs. To examine the net effect of simultaneous plasticity of inhibition and excitation on Purkinje cell output with a feed-forward input, I simulated synaptic inputs with dynamic clamp and systematically changed the ratio of excitation and inhibition as well as the amplitude of both components. Depressing both components as observed when pairing the isolated components with the climbing fibre, reduced spike output for feed-forward inputs with small inhibitory components, while for inputs with stronger inhibition the spike output increased. Finally, I showed that pauses after spike bursts evoked by strong parallel fibre inputs in the absence of inhibition scaled with input strength. A classical climbing fibre LTD protocol reduced these pauses, which thus encode information stored by synaptic plasticity for downstream neurons. These findings are discussed in the context of classical theories of cerebellar learning, which are concluded to require revision or refinement.
43

Analysis of memory consolidation and reconsolidation in the mouse hippocampus

von Hertzen, Laura Sisko Johanna January 2005 (has links)
Our brain processes enormous amounts of information subserving the formation and retrieval of memory. A fresh memory is an unstable trace that is stabilised by a process termed consolidation. This depends on de novo transcription. Reactivating a stabilised memory returns it to a labile state, and triggers a second consolidation process, termed reconsolidation, re-stabilising the memory again. This study used two transcriptional screens to determine the molecular relationship between consolidation and reconsolidation. Three immediate-early genes were identified to be regulated in the hippocampus after contextual fear conditioning in the mouse: Serum and Glucocorticoid regulated Kinase 1 (SGKl), SGK3 and Nerve Growth Factor Inducible gene B (NGFI-B). The up-regulation of SGKl expression was triggered by the environment, and thus SGK-1 might be important for the formation of a contextual representation. The up- regulation of SGK3 and NGFI-B expression was specific to the context-shock association, suggesting a role for these genes in the consolidation of the context-shock association. Re-exposure of the mice to the context reiterated the upregulation of SGKl and SGK3 expression, demonstrating that some transcriptional events after contextual conditioning are recapitulated during reconsolidation, and showing for the first time that an expression change specific to the context-shock association (SGK3) can be subsequently recapitulated during reconsolidation. It was also established that the transcriptional changes induced by retrieval depended on the remoteness of the reactivated memory. In contrast to SGKl and SGK3, NGFI-B was not regulated during reconsolidation, and therefore was specific to memory consolidation. This consolidation-specific regulation of NGFI-B was confined to hippocampal area CAl and required ?CaMKll autophosphorylation. This finding suggests a link between synaptic activity and gene regulation in memory formation. Functional studies of NGFI-B showed that NGFI-B was important for hippocampus-dependent memory formation. The discovery of this consolidation-specific transcript indicates that reconsolidation is only a partial recapitulation of consolidation at the transcriptional level.
44

fMRI investigation of a model of direct cortical stimulation in rodent brain

Austin, Vivienne Catherine Marie January 2003 (has links)
No description available.
45

Investigating stimulus induced metabolic changes in human visual cortex using functional magnetic resonance spectroscopy at 7T

Lin, Yan January 2011 (has links)
This thesis concerns the investigation of metabolic changes in 1H metabolite levels in the human visual cortex due to visual stimulation using proton magnetic resonance spectroscopy (1H-MRS) at 7T. The work described in this thesis has been undertaken by the author and collaborators at the Sir Peter Mansfield Magnetic Resonance Centre at the University of Nottingham. Detection of functional changes in 1H metabolites may enable a greater understanding of neurotransmitter activity and metabolic pathways used for energy synthesis during activation of brain tissue. Previous 1H MRS studies of the activated human brain mainly focused on observing lactate (Lac) changes. More recent studies by Mangia et al, taking advantage of the increased signal and spectral resolution at 7T, have investigated the change in the level of Lac, glutamate (Glu), Aspartate (Asp) and Glucose (Glc) during activation. However, Mangia, did not measure significant change in the level of gamma aminobutyric acid (GABA) and Glutamine (Gln), which might be expected to change due to increased neurotransmitter cycling rates during activation. Given that the metabolite changes observed due to visual stimulation were relatively small. We used a long, intense visual stimulus, designed to retain attention, to confirm and quantify the changes in the levels of Glu, GABA, and Gln, and to further investigate the Lac and Asp response to visual stimulation. Our present results using a moving stimulus of full-screen flickering contrast-defined wedges, have demonstrated many more metabolic changes throughout two different time scales of stimulation. Small (2~11%) but significant stimulation induced increases in Lac, Glu and glutathione (GSH) were observed along with decreases in Asp, GIn and glycine (Gly). In addition, decreases in (intracellular) Glc and increases in GABA were seen but did not reach significance. The opposite changes in Glu and Asp are indicative of increased activity of the malate-aspartate shuttle, which taken together with the opposite changes in Glc and Lac reflect the expected increase in brain energy metabolism. The increases in Glu and GABA coupled with the decrease in GIn can be interpreted in terms of increased activity of the Glu/Gln and Gln/Glu/GABA neurotransmitter cycles. An entirely new observation is the increase of GSH during prolonged visual stimulation. The similarity of its time course to that of Glu suggests that it may be a response to the increased release of Glu or to the increased production of reactive oxygen species. Gly is also a precursor of GSH and a decrease on activation is consistent with increased GSH synthesis. Together these observations constitute the most detailed analysis to date of functional changes in human brain metabolites. Interestingly, the Lac response was confined to the first visual stimulus. It is possible that processes triggered during the first period of visual stimulation, could continue for a while after stimulation has ended. If this is an important mechanism of the activity-stimulated brain Lac response, shortening the duration of the first stimulus might lead to an increase in Lac response during the second period of stimulation. With this in mind, we designed a repeated visual stimulation paradigm, varying the duration of the first stimulation (shorter than 9.9-min, based on our previous results), to see the effect on the Lac response during the second visual stimulation period. A gradual increase in Lac under the prolonged stimulation, following the first brief stimulation (1s, 16s and 48s, respectively), was observed and maintained until the end of these periods. Lac responses during the second stimulation period looked similar whether the first stimulation was 1s or 16s. With the increase of first visual stimulus duration (48s), the Lac response under the second stimulation period was slightly diminished. No significant Lac accumulation can be evident to the second stimulation, when the initial stimulation was 288s. The averaged Lac level was considerably below baseline after cessation of the first 288s stimulus. It is possible that the increased glycolytic flux, triggered during the initial longer stimulation, would still continue for a while during recovery, accounting for the decreased brain Lac level during resting periods from stimulation. Further experiments are ongoing, varying the duration of the second resting periods, to see the effect on the Lac response to the second stimulation.
46

Μελέτη της αποσιώπησης του γονιδίου της Geminin στα πρόδρομα κύτταρα του εγκεφαλικού φλοιού κατά την δέκατη τέταρτη εμβρυϊκή ημέρα (Ε14,5) του μυός

Κυρούση, Χριστίνα 29 August 2011 (has links)
Ο εγκεφαλικός φλοιός των θηλαστικών σχηματίζεται από το πιο πρόσθιο τμήμα του νευρικού σωλήνα, τον προσεγκέφαλο. Η ανάπτυξη του εγκεφαλικού φλοιού είναι μια διαδικασία που περιλαμβάνει την σωστή οργάνωση των πρόδρομων νευρικών κυττάρων σε συγκεκριμένες περιοχές του αναπτυσσόμενου φλοιού καθώς επίσης και την εμφάνιση τους σε καθορισμένη χρονική στιγμή κατά την πορεία της ανάπτυξης. Κατά την νευρογένεση όλοι οι νευρώνες του εγκεφαλικού φλοιού προέρχονται από το νευροεπιθήλιο που βρίσκεται δίπλα από τις πλευρικές κοιλίες. Τα νευροεπιθηλιακά κύτταρα αρχικά διαιρούνται με σκοπό την δημιουργία ικανού αριθμού πρόδρομων κυττάρων που θα μπορέσουν να δώσουν γένεση στον αναπτυσσόμενο φλοιό. Αργότερα, τα κύτταρα αυτά, διαφοροποιούνται προς τις άλλες κατηγορίες πρόδρομων κυττάρων και προς τους διαφοροποιημένους νευρώνες. Η ανάπτυξη του εγκεφαλικού φλοιού είναι μια διαδικασία που απαιτεί τον έλεγχο της ισορροπίας μεταξύ του πολλαπλασιασμού και της διαφοροποίησης των πρόδρομων νευρικών κυττάρων. Η Geminin έχει δειχτεί ότι ρυθμίζει τον κυτταρικό πολλαπλασιασμό και την διαφοροποίηση αποτελώντας έναν συνδετικό κρίκο μεταξύ των δυο αυτών διαδικασιών. Με σκοπό να διερευνήσουμε τον in vivo ρόλο της Geminin στη διατήρηση και διαφοροποίηση των πρόδρομων νευρικών κυττάρων του εγκεφαλικού φλοιού του μυός, αδρανοποιήσαμε το γονίδιο της Geminin ειδικά στα κύτταρα του αναπτυσσόμενου εγκεφαλικού φλοιού. Τα αποτελέσματα μας έδειξαν ότι η απαλοιφή της Geminin έχει ως αποτέλεσμα την επέκταση της κοιλιακής ζώνης του φλοιού ως συνέπεια της παραγωγής μεγαλύτερου αριθμού πρόδρομων κυττάρων στην κορυφαία περιοχή του φλοιού. Επιπλέον η απώλεια του γονιδίου της Geminin αυξάνει τον καθορισμό των βασικών προγονικών κυττάρων της υποκοιλιακής ζώνης του φλοιού. Ως άμεσο επακόλουθο η αύξηση του αριθμού των πρόδρομων κυττάρων στις νευρογενετικές ζώνες του φλοιού είναι η παραγωγή μεγαλύτερου αριθμού πλήρως διαφοροποιημένων νευρικών κυττάρων στον εγκεφαλικό φλοιό. Η μελέτη μας αναδεικνύει την Geminin ως μόριο κλειδί κατά την πορεία της ανάπτυξης του εγκεφαλικού φλοιού, στον καθορισμό του σωστού αριθμού των πρόδρομων κυττάρων, στην πορεία διαφοροποίησης αυτών και τελικά στον σχηματισμό του σωστού αριθμού των πλήρως διαφοροποιημένων νευρώνων. / The mammalian cerebral cortex originates from the most anterior part of the neural tube, the prosencephalon. The cortical development is a process that involves the correct orchestration of the different neuronal progenitor lineage of the cortex, which involves the regional patterning of progenitors and their temporal specification during neurogenesis. During neurogenesis, the cortical neurons are originated from the neuroepithelium that lies next to the lateral vesicles. At the beginning, the neuroepithelial cells divide in order to expand their population and to create the essential number of progenitor cells that would give rise to the neurons and glia that comprise the cortex, a procedure called self-renewal. Later on, the neuroepithelial cells start to switch from divisions that generate additional progenitor cells to divisions that generate committed progenitors or postmitotic cells. The development of cerebral cortex is a process that requires coordination of proliferation and differentiation of progenitor cells. It has been proposed that Geminin regulates both cell proliferation and differentiation. In order to investigate the in vivo role of Geminin in the maintenance and the differentiation of the neuronal progenitors of the cerebral cortex, we specifically inactivated the mouse Geminin gene in the developing cortex. Our results indicate that deletion of Geminin results in the expansion of the ventricular zone that leads to the production of a higher number of the apical cortical progenitors at the middle stage of cortical neurogenesis. In addition, the depletion of Geminin influences the number of basal progenitor of the subventricular zone. The increase of the apical and basal progenitor cells results in the overproduction of differentiated neurons of the developing cortex. Our work demonstrates Geminin as an important molecule for the development of the mouse cerebral cortex, regulating the correct number of cortical progenitors and the generation of the correct number of neurons and glial cells of the cerebral cortex.
47

Processing symbols in the ventral visual cortex : functional architecture and anatomical constraints

Bouhali, Florence 28 November 2017 (has links)
Le cortex visuel ventral chez l’homme se compose d’une mosaïque de régions spécialisées dans la reconnaissance de différentes catégories d’objets. Selon une organisation reproductible, certaines régions répondent préférentiellement aux visages, alors que d’autres sont plus activées par les maisons et les lieux, par les outils, ou encore par les parties du corps. Plusieurs facteurs ont été invoqués pour expliquer la préférence d’une région pour une catégorie donnée, tels que des biais pour le traitement de certaines caractéristiques visuelles (préférence pour la position fovéale ou périphérique des stimuli, pour leur fréquence spatiale haute ou basse), le degré d’exposition et d’expertise (expertise pour les voitures par exemple), ou la connectivité anatomique vers des réseaux cérébraux spécialisés dans le traitement d’un domaine particulier. Chez les enfants, l’apprentissage de la lecture de mots ou d’autres systèmes symboliques culturels provoque le développement de régions corticales dédiées, telles que l’aire de la forme visuelle des mots (VWFA), au sein d’une voie ventrale en partie déjà stabilisée. Ce développement ontologique tardif pour la reconnaissance de symboles, indépendamment de contraintes phylogénétiques propres à la lecture, facilite l’étude de ce qui façonne la spécialisation fonctionnelle au sein de la voie ventrale. Dans cette thèse, nous avons étudié la représentation des mots et des partitions de musique au sein du cortex visuel ventral en combinant des méthodes d’imagerie par résonance magnétique fonctionnelle et de diffusion, à des taches comportementales. D’abord, nous montrons que la localisation de la VWFA chez les adultes correspond, en comparaison à des régions voisines du cortex ventral, à une région connectée de manière optimale à celles du langage qui traitent le contenu sémantique et phonologique. Ensuite, nous montrons que les régions ventrales qui sous-tendent le décodage orthographique sont fonctionnellement hétérogènes selon un axe latero-médial. Les régions médianes semblent encoder les graphèmes de façon sérielle, sous le contrôle de régions pariétales, pour les convertir en phonèmes. A l’inverse, les régions latérales traitent les mots de façon plus flexible pour accéder au lexique. Ces études mettent en évidence le rôle majeur de la connectivité anatomique dans le développement d’une spécialisation fonctionnelle pour les mots, avec la contribution de connectivités diverses qui participent à l’hétérogénéité fonctionnelle du système de la forme visuelle des mots. Enfin, nous observons que la maîtrise de la lecture musicale a d’importantes conséquences sur la latéralisation ventrale d’autres catégories. D’une part, la latéralisation à gauche augmente dans des régions latérales ventrales pour toutes les catégories. D’autre part, la latéralisation à droite augmente dans des régions fusiformes postérieures, notamment pour le traitement des visages et des maisons. Ces conséquences, similaires à celles provoquées par l’apprentissage de la lecture de mots, révèlent des processus à la fois de compétition et de transfert entre catégories. Ainsi, nos résultats suggèrent que des mécanismes communs pourraient expliquer comment une expertise culturelle peut recycler et modifier le cortex visuel. / The human ventral visual cortex hosts a mosaic of areas specialized in the recognition of different categories of objects. According to a reproducible pattern, some areas respond preferentially to faces, while others are more activated by places and buildings, by tools, or by body parts. Several factors have been proposed as major determinants of the preferred category of a given region, such as visual feature biases (preference for peripheral vs. foveal stimuli, or for high vs. low spatial frequencies), experience (e.g., car expertise) and white-matter connectivity to domain-specific brain networks. In children, learning to read words and other cultural symbols triggers the emergence of dedicated cortical areas, such as the visual word form area (VWFA), within a partially settled ventral pathway. This late ontological development for symbol recognition, free from reading-specific evolutionary constraints, facilitates the investigation of what shapes functional specialization in the ventral pathway. In the current work, we studied in particular the representation of words and musical scores in the ventral visual cortex, using functional magnetic resonance imaging (fMRI), diffusion-weighted imaging and behavioral tasks. First, we show that the location of the VWFA in adults corresponds to a region optimally connected to language regions supporting semantics and phonology, as compared to adjacent ventral cortex regions. Second, we demonstrate that ventral regions supporting orthographic decoding are heterogeneous along a medial-to-lateral axis. Medial regions seem to encode graphemes serially for phonological decoding, under the control of parietal regions. In contrast, lateral regions process words more flexibly for lexical access. These studies reveal a major role of white-matter connectivity in shaping functional specialization for words, with differential connections participating in the functional heterogeneity of the VWFA. Third, we observe that musical literacy has a large impact on lateralization patterns in the ventral stream. A domain general enhancement of leftward lateralization takes place in lateral ventral regions, together with a rightward shift in fusiform regions notably for the processing of faces and houses. These consequences probably reflect both competition between visual categories and transfer across them, and resemble the impact of reading acquisition. Together, our results show that common processes may explain how cultural expertise recycles and modifies the visual cortex.
48

Investigating the mechanism by which thalamocortical projections reach the cerebral cortex

Chen, Yijing January 2012 (has links)
This thesis provides insights into the mechanism by which thalamocortical axons (TCAs) approach the cortex from their origin in the thalamus. Previous studies suggested that the reciprocal projections from the prethalamus and the ventral telencephalon guide TCAs to descend through the prethalamus and cross the diencephalic-telencephalic boundary (DTB), after which TCAs navigate through permissive corridor cells in the ventral telencephalon and cross the pallial-subpallial boundary (PSPB) before reaching their final targets in the cortex. The ‘Handshake Hypothesis’ proposed that pioneer axons from cortical preplate neurons guide TCAs into corresponding cortical areas. However, there is a lack of convincing evidence on whether TCAs need any guidance to cross the PSPB. In the current study, Adenomatous polyposis (Apc) gene is conditionally deleted from the cortex, by using Emx1Cre-APCloxP recombination technology. Apc is widely expressed in the nervous system including the cortical plate of the cortex and regulates axonal growth and neuronal differentiation. Deleting Apc may block neurite extension and/or affect the formation of attractive or repulsive cues in the cortex. By using DiI tracing as well as L1 immunohistochemistry techniques, I showed that in the Apc mutants cortical axons are absent and that TCAs initially navigate into the ventral telencephalon normally but fail to complete their journey into the cortex. They stop as they approach the PSPB, although the PSPB doesn’t seem to be directly affected by the mutation of Apc in the cortex. Additionally, Ig-Nrg1 (Neuregulin-1), the secreted protein that was suggested to play long-range roles in attracting TCAs towards the cortex, is present in the Apc mutant. This implies that Ig-Nrg1 is not sufficient for guiding TCAs into the cortex, and that additional guidance factors are needed. Moreover, my in vitro explant culture experiments show that the mutant cortex neither repel nor inhibit thalamic axonal outgrowth, indicating that the failure of TCAs in reaching the cortex is not due to the change of repulsive cues secreted by the mutant cortex. It rather indicates that the guidance factors for TCAs are likely to function through cell-cell contact mediated mechanisms. The Apc mutant cortex lacks these guidance factors, which might be the cortical axons. In conclusion, my data reveal a choice point for TCAs at the PSPB. Guidance factors from the cortex are needed for TCAs to cross the PSPB, which are absent in the Apc mutant. TCAs may need the direct contact with cortical axons and use them as an axonal scaffold to navigate into the cerebral cortex.
49

The role of MeCP2 in activity-dependent brain processes

Mcleod, Faye Christine January 2012 (has links)
Rett syndrome (RTT) is a neurodevelopmental disorder that is caused by mutations in the X-linked gene MECP2 and results in cognitive impairment, epilepsy and motor dysfunction. Deletion or silencing of Mecp2 in the brain of mice recapitulates many of the main phenotypes of the disorder and has been fundamental in understanding the actions of MeCP2 although the precise molecular function remains unknown. MeCP2 is classically thought to have a role in repressing gene transcription through recruitment of histone deacetylase proteins. Studies have also shown that Mecp2 can be modified posttranslationally in response to neuronal activity. The aim of this thesis was to investigate the activity-dependent alterations in MeCP2 and the association this has with levels of acetylated histone proteins, a marker of active gene transcription thus gaining a better insight into how neuronal activity affects the function of MeCP2. Furthermore at the network level, a second objective was to characterise the effects loss of functional MeCP2 has on the regulation of network circuitry in the brain and in particular the development of epileptiform activities. To study this I focussed on the hippocampus in wild-type and Mecp2 mutant mice and in vivo administered the convulsant drug kainic acid (25mg/kg; IP) followed by seizure scoring and in vitro by application of various epileptogenic agents (kainic acid, bicuculline and 4-aminopyridine) to acute hippocampal slices. Having characterised the network properties, I then quantified protein alterations in phosphorylation of Mecp2, acetylated histone H3 and H4 and immediate early genes, c-Fos and Egr-1 in the hippocampus using western blot and quantitative immunohistochemistry techniques. Based on a modified seizure scale (eight stages with lower being less severe), administration of kainic acid in vivo to Mecp2-deficient male mice resulted in a higher seizure score (mean = 6 ± 0.7 vs. 4 ± 0.2 units in wild-type) and more rapid onset (77% of mice show seizures after 10 minutes compared to 5% of wild-type mice). Field recording data collected in vitro following application of kainic acid to hippocampal slice from Mecp2-deficient mice show a significant increase in gamma power oscillation (1059 ± 379µV2) compared to slices from WT mice (287 ± 178µV2) which had a lower mean power. Application of bicuculline revealed hippocampal slices from Mecp2-deficient mice had increased frequency of spontaneous epileptiform field events (1µM and 3µM bicuculline) and elevated duration of spontaneous and evoked epileptiform field events (10µM bicuculline). Similarly, 4-aminopyridine (4-AP) administration to hippocampal slices resulted in Mecp2-deficient mice displaying increased frequency of spontaneous field events (50µM 4-AP) and epileptic ictal-like events (88% of slices from Mecp2stop/y mice displayed these events compared to 43% of slices from WT mice). Furthermore there was an increase in spontaneous and evoked field events following application of 30µM and 10µM 4-AP. Western blot experiments using hippocampal extracts from WT and Mecp2-deficient male mice treated with the convulsant drug kainic acid or saline (vehicle control) revealed Mecp2 is highly phosphorylated at serine 421 (3.4 ± 0.5 fold, p< 0.01) upon induction of neuronal activity compared to saline controls but there was no change in histone H3 or H4 acetylated proteins. A complementary quantitative immunohistochemistry approach was used to assess variations in histone H3 or H4 acetylated proteins at the single cell level from heterozygous female mice (displaying a mosaic expression of Mecp2) treated with kainic acid or saline. These results revealed there was no difference in the levels of either acetylated histone H3 of H4 protein between Mecp2 positive and negative nuclei. However there was a clear cell-autonomous effect in terms of a 5% reduction in the nuclear volume of Mecp2-deficient cells. Quantification of immediate early gene signal in Mecp2+/- heterozygous female mice treated with kainic acid or saline using the same immunohistochemistry method showed there was no difference in the distribution of c-Fos intensities between Mecp2 positive and negative nuclei following any treatment. However there was a greater proportion of Mecp2-deficient nuclei (~20%) expressing c-Fos under saline control conditions and following neuronal activity. Furthermore there was a reduction in the percentage of Mecp2 negative nuclei in the top 25% of Egr-1 intensities in the CA1 following three hours of neuronal activity (33.5 ± 2.3% for Mecp2 negative nuclei and 19.1 ± 1.7% for Mecp2 positive nuclei). In summary my results show at the network level there is a reduction in seizure threshold and increase power of gamma oscillations in the hippocampus of Mecp2-deficient mice which could lead to a state of network hyperexcitability and switch activities from physiological oscillatory rhythms to more pathological ones. An imbalance in inhibitory neuron regulation could partially contribute to alterations in network excitability to overall promote epileptogenesis. At the cellular level I report that Mecp2 can become phosphorylated following induction of neuronal activity but this is not associated with alterations in global histone acetylation. Nonetheless Mecp2-deficient cells display a reduction in nuclear volume and have alterations in c-Fos and Egr-1 levels following induction of neuronal activity. Overall my data contribute to the understanding of how the presence or absence of MeCP2 affects network excitability and how in turn neuronal excitability affects MeCP2 phosphorylation, histone acetylation and the activation of immediate early genes.
50

Characterising structural and functional changes in the adolescent brain

Lloyd, William K. January 2012 (has links)
Brain maturation is an important factor in cognitive, emotional, behavioural and motor development during childhood and adolescence. This study uses multi-modal magnetic resonance imaging (MRI) techniques to assess neural representations of devel opment in both healthy and abnormally developing populations. A novel face emotion stimulus set, designed to assess distinct dimensions of facial emotion, particularly to assess the e ect of averted faces, is introduced in a pilot functional MRI study of an adult cohort. Results from this pilot study show that interactions between face direction and emotion can infuence which brain areas are recruited for emo- tion processing, suggesting that the neural correlates of judging facial emotion content are modulated by face direction. Facial emotion perception was assessed as a neural task to investigate dimensions of emotion processing, and emotion processing development, in a group of children and adolescents. A number of correlations were found between dimensions of the task and developmental measures such as age, pubertal development and intelligence. In particular, intelligence was shown to be positively associated with the increasing utilization of regions associated with cognitive control, such as the prefrontal cortex. A voxel-based morphometry (VBM) study explored potential structural correlates of adolescent development. Age was found to correlate with changes in local brain regions, however pubertal development was shown to be a more accurate measure of those changes. A diusion tensor imaging assessment of white matter using fractional anisotropy has demonstrated important developmental di erences in white matter be- tween males and females over childhood and adolescence. Findings also suggest diff erent relationships between intelligence and white matter for males and females. Developmental Coordination Disorder, a common childhood disorder characterised by deficits in learning and automating motor skills, was assessed as an example of ab normal brain development. VBM was used to show that kinematic metrics of a simple visuomotor task correlated with regional grey matter volumes.

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