The molecular mechanisms that coordinate postnatal brain enlargement, synaptic properties and cognition remain an enigma. This study demonstrates that neuronal complexity controlled by p21-activated kinases (PAKs) is a key determinant for postnatal brain enlargement and synaptic properties. Double knockout (DK) mice lacking both PAK1 and PAK3 were severely impaired in postnatal brain growth, resulting in a dramatic reduction in brain volume at maturity. Remarkably, the reduced brain was accompanied by minimal changes in total cell count, due to a significant increase in cell density. However, the DK neurons have smaller soma, markedly simplified dendritic arbors/axons and reduced synapse density. Surprisingly, the DK mice were elevated in basal synaptic responses due to enhanced individual synaptic potency, but severely impaired in bi-directional synaptic plasticity. The PAK1/3 action is likely mediated by cofilin-dependent actin regulation because the activity of cofilin and the properties of actin filaments were specifically altered in the DK mice.

Frequenin (Frq) and its mammalian homologue, Neuronal Calcium Sensor 1 (NCS-1), are calcium-binding proteins, which regulate neurotransmitter release. However, reports are contradictory, and little is known about Frq's cellular mechanisms. The Drosophila nervous system can be used to gain a better understanding of the function of Frq. There are two Frq-encoding genes in Drosophila. The temporal and spatial expression patterns of the two genes are very similar, and the proteins they encode, Frq1 and Frq2, are 95% identical in amino acid sequence. Loss-of-function phenotypes were studied using three different procedures: creating a deletion designed to remove the entire frq1 gene and part of the frq2 gene; using an interfering C-terminal peptide to prevent Frq binding to its intracellular targets; and using RNAi to reduce frq1 and frq2 transcript levels. Deletion of the entire frq1 gene and part of the frq2 gene resulted in impaired neurotransmitter release and enhanced nerve terminal growth. To discriminate chronic from acute loss-of-function effects, the effects of transgenic expression and forward-filling an interfering C-terminal peptide into presynaptic terminals were compared. In both cases, a reduction in quantal content per bouton occurred, demonstrating that this trait does not result from homeostatic adaptations during development. The chronic treatment also enhanced nerve terminal growth. Conversely, gain-of-function conditions yielded an increase in quantal content and a reduction in nerve terminal growth. Frqs' effects on transmitter output were not due to changes in the number of active zones, nor were they due to changes in the size of the readily releasable pool of vesicles. Oregon Green 488 BAPTA-1 conjugated to 10 kDa Dextran was forward-filled into presynaptic boutons to detect changes in presynaptic Ca2+ signals. Ca2+ responses to presynaptic nerve impulses demonstrated that Frq modulates neurotransmitter release by regulating Ca2+ entry. Gain-of-function phenotypes remained present in a PI4KB null background, demonstrating that Frq's effects were not due to an interaction with PI4KB. All effects seen for all studies were identical for both Frqs, indicating that the two Frq proteins are likely functionally redundant. Overall, Frqs have two distinct functions: one on neurotransmission, primarily by regulating Ca2+ entry, and another on axonal growth and synaptic bouton formation.

In addition to acting in synaptic transmission, neurotransmitters have been shown to play roles in the development of nervous system. Developing neurons extend neurites to connect to their target cells, and growth cones at the tip of growing neurites are critical for pathfinding. Although evidence for the regulation of axonal growth and growth cone guidance by neurotransmitters and neuromodulators is emerging, less is known about the mechanisms by which neurotransmitters affect developing neurons. Here, I focus on three neurotransmitters/ neuromodulators and describe their actions (a) at the level of growth cone, especially on filopodia, which serve as sensors that allow growth cones to probe the environment they are traversing, and (b) on how neurotransmitters modulate neuronal electrical properties, which, in itself, have been shown to affect neurite extension. The goals of this dissertation are to investigate 1) the cholinergic modulation of neuronal activity and its effects on growth cone motility; 2) the excitatory modulation of neuronal excitability by nitric oxide (NO); and 3) the inhibitory modulation of neuronal activity by dopamine (DA). The work uses a well-established model system to investigate growth cone motility and neuronal activity: identified neurons from the pond snail Helisoma trivolvis studied in cell culture or in the intact ganglion in situ. The study of B5 neurons demonstrates that acetylcholine (ACh) induces filopodial elongation, which is mediated by opening of nicotinic ACh receptors, membrane depolarization, and elevation of intracellular Ca level in growth cones. This dissertation also shows that NO inhibits two types of Ca-activated K channels to depolarize the membrane potential of B19 neurons. Additionally, the study reveals that DA serves as an inhibitory neurotransmitter to hyperpolarize and silence the electrical activity of firing B5 neurons via a D2-like receptor/PLC/K channel pathway. Taken together, this dissertation elucidates novel cellular mechanisms through which neurotransmitters can regulate growth cone motility and neuronal electrical properties, further supporting evidence for potential roles of neurotransmitters in axon pathfinding and synaptic transmission in vivo.

In addition to acting in synaptic transmission, neurotransmitters have been shown to play roles in the development of nervous system. Developing neurons extend neurites to connect to their target cells, and growth cones at the tip of growing neurites are critical for pathfinding. Although evidence for the regulation of axonal growth and growth cone guidance by neurotransmitters and neuromodulators is emerging, less is known about the mechanisms by which neurotransmitters affect developing neurons. Here, I focus on three neurotransmitters/ neuromodulators and describe their actions (a) at the level of growth cone, especially on filopodia, which serve as sensors that allow growth cones to probe the environment they are traversing, and (b) on how neurotransmitters modulate neuronal electrical properties, which, in itself, have been shown to affect neurite extension. The goals of this dissertation are to investigate 1) the cholinergic modulation of neuronal activity and its effects on growth cone motility; 2) the excitatory modulation of neuronal excitability by nitric oxide (NO); and 3) the inhibitory modulation of neuronal activity by dopamine (DA). The work uses a well-established model system to investigate growth cone motility and neuronal activity: identified neurons from the pond snail Helisoma trivolvis studied in cell culture or in the intact ganglion in situ. The study of B5 neurons demonstrates that acetylcholine (ACh) induces filopodial elongation, which is mediated by opening of nicotinic ACh receptors, membrane depolarization, and elevation of intracellular Ca level in growth cones. This dissertation also shows that NO inhibits two types of Ca-activated K channels to depolarize the membrane potential of B19 neurons. Additionally, the study reveals that DA serves as an inhibitory neurotransmitter to hyperpolarize and silence the electrical activity of firing B5 neurons via a D2-like receptor/PLC/K channel pathway. Taken together, this dissertation elucidates novel cellular mechanisms through which neurotransmitters can regulate growth cone motility and neuronal electrical properties, further supporting evidence for potential roles of neurotransmitters in axon pathfinding and synaptic transmission in vivo.

Ce travail étudie le potentiel des RNA pour l'estimation détaillée des coûts de projet dans le domaine des infrastructures municipales. En général, pour l'entrepreneur en construction civile, l'obtention d'un contrat se joue lors des soumissions publiques. Subséquemment, l'estimation des coûts de travaux constitue la pierre angulaire de ce processus de soumission. Cette tâche s'avère vite laborieuse considérant le nombre élevé d'éléments dont il faut tenir compte, et de plus, la valeur de chacun de ces éléments est fonction de plusieurs variables difficilement contrôlables. Il a été démontré que l'attribution du taux de productivité d'une équipe de travail est la source majeure d'erreur lors de la préparation des estimations détaillées. Nous avons bâti un modèle de prédiction du taux de productivité d'une équipe d'installation de réseaux d'aqueduc et d'égouts. Les données qui ont servi à valider empiriquement le modèle proposé émanent de projets exécutés dans la région de Laval et des Basses-Laurentides. Un historique de données est construit à partir des rapports journaliers de surveillance des travaux de 43 projets de génie urbain. Afin d'explorer la capacité des RNA à imiter le jugement et l'expérience d'un estimateur chevronné. Deux forums de discussion ont eu lieu avec trois estimateurs du domaine pour déterminer les facteurs qui influencent le taux de productivité de l'équipe d'excavation de tranchées. Ces discussions ont permis de déterminer le jeu optimal des données d'entrée des RNA. Trois estimateurs chevronnés ont également calculé manuellement le taux de productivité à partir des plans et devis de chacun des deux projets testés. Pour ces deux projets, les résultats de prédiction des RNA sont comparés aux résultats des trois estimateurs ainsi qu'au taux de productivité réel obtenu au chantier. Les RNA obtiennent des résultats supérieurs au niveau de la précision par rapport aux résultats des estimateurs. Des recommandations sont faites pour la préparation des futurs rapports journaliers de surveillance de travaux afin de rendre les données plus accessibles aux RNA. Ainsi, d'autres recommandations sont faites pour des recherches futures qui permettraient d'introduire le processus de prédiction dans les logiciels commerciaux d'estimation détaillée du coût de projet. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Réseau de neurones artificiels (RNA), Estimation, Génie civil, Prédiction.

<p>Perception arises from sensory inputs detected by peripheral organs and processed in the brain by complex neuronal circuits required for the integration of external information with internal states such as expectation and attention. Stimulus discrimination requires activation of primary sensory areas in the brain, but expectation is traditionally associated with the activation of higher-order brain areas. Sensory information obtained by tactile organs is represented along the primary areas that comprise the trigeminal thalamocortical pathway. In anesthetized animals, neuronal activity in the somatosensory system has been extensively described over the past century. However, it is still unclear how the different thalamocortical structures contribute to active tactile discrimination and represent relevant features of the stimulus. It is also unknown whether expectation modulates tactile representations in these regions. In this dissertation, I investigated neuronal ensemble activity recorded from freely behaving rats performing a whisker-based tactile discrimination t-+ask. Multielectrode arrays were chronically implanted to record simultaneously from the main stages of the trigeminal thalamocortical pathways involved in whisking: the primary somatosensory cortex (S1), the ventral posterior medial nucleus of the thalamus (VPM), the posterior medial complex (POm) and the zona incerta (ZI). In Chapter 1 I describe the behavior of rats performing the tactile discrimination task, which requires animals to associate two different tactile stimuli with two corresponding choices of spatial trajectory in order for reward to be delivered. I found that both cortical and thalamic neurons are dynamically engaged during execution of the task. The data reveal a very complex mosaic of responses comprising single or multiple periods of inhibition and excitation. Thalamocortical activity was modulated during whisker stimulation as well as after stimulus removal, up until reward delivery. To investigate whether reward expectation plays a role in tactile processing at early processing stages, I also recorded neuronal activity from rats performing a freely-rewarded version of the tactile discrimination task. Comparing data from regularly-rewarded and freely-rewarded sessions, I show in chapter 2 that the activity of single neurons in the primary somatosensory thalamocortical loop is strongly modulated by reward expectation. Stimulus-related information coded by primary thalamocortical neurons is high when a correct association between stimulus and response is crucial for reward, but decreases significantly when the association is irrelevant. These results indicate that tactile processing in primary somatosensory areas of the thalamus and cerebral cortex is directly affected by reward expectation.</p> / Dissertation

Sexual differentiation is divided into gonadal sexual differentiation and brain sexual differentiation in the teleosts. Gonadal sexual differentiation is regulated by brain sexual differentiation. Brain sexual differentiation is resulted from the neural development, which lead to the sexual dimorphism of both structure and functions of brain. The neural development is influenced by the genetic factors and the external environmental factors. The lower temperature induces a higher proportion of female while the elevated temperature induces a higher proportion of male in tilapia. In addition, there is sexual difference in effects of temperature on the activity of brain neurochemicals. Water temperature plays an important role on the development of central neurotransmitter systems and sexual differentiation during the developing period. In the present study, the primary neural culture cloned from the female and male tilapia¡AOreochromis mossambicus was used. The difference of the physiological characteristics between the neural cells derived from the females and males, were investigated. These results show that the elevated temperature has an effect to enhance the proliferation in both primary neural culture of females and males.

The Knife-Edge Scanning Microscope (KESM) enables imaging of an entire mouse brain at sub-micrometer resolution. By using the data sets from the KESM, we can trace the neuronal and vascular structures of the whole mouse brain. I investigated effective methods for automatic seedpoint selection on 3D data sets from the KESM. Furthermore, based on the detected seedpoints, I counted the total number of somata and traced the neuronal structures in the KESM data sets. In the first step, the acquired images from KESM were preprocessed as follows: inverting, noise filtering and contrast enhancement, merging, and stacking to create 3D volumes. Second, I used a morphological object detection algorithm to select seedpoints in the complex neuronal structures. Third, I used an interactive 3D seedpoint validation and a multi-scale approach to identify incorrectly detected somata due to the dense overlapping structures. Fourth, I counted the number of somata to investigate regional differences and morphological features of the mouse brain. Finally, I traced the neuronal structures using a local maximum intensity projection method that employs moving windows. The contributions of this work include reducing time required for setting seedpoints, decreasing the number of falsely detected somata, and improving 3D neuronal reconstruction and analysis performance.

No description available.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains vii, 79 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 70-78).