Browsing by Subject "Hippocampus"

Now showing 1 - 5 of 5
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    Actin Isoforms in neuronal structure and function
    (2011-07) Cheever, Thomas R.
    The actin cytoskeleton plays critical roles in nearly every aspect of neuronal development and function. During these processes, the localized polymerization of actin is one mechanism employed to carryout crucial tasks for normal neuronal function. While the activity of actin binding proteins is generally thought to be the primary mediator of spatially restricted actin polymerization, another prominent mechanism involves the local translation of β-actin, one of two actin isoforms expressed in neurons. The localized translation of β-actin has been shown previously to be essential for growth cone guidance in cultured neurons. Additionally, defects in the localization of β-actin have been implicated in the motor neuron disease Spinal Muscular Atrophy (SMA). However, no study to date has directly examined the role of β-actin in a mammalian in vivo system. Although the functions of β-actin were thought to be critical for all neurons, the work described in this thesis indicates that specific functions of β-actin are surprisingly confined to select populations in the central nervous system (CNS). β-actin is not required for motor axon regeneration or motor neuron function, but is required for the proper structure of the hippocampus, cerebellum, and corpus callosum, as well as hippocampal-associated behaviors. Thus, the work described here provides the first direct demonstration of specific roles for β-actin in vivo and presents a model to translate provocative findings in cell culture to the mammalian CNS.
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    Early iron deficiency anemia alters structure in pyramidal neuron apical dendrites and cytoskeletal modifiers associated with dendrite development in the hippocampus.
    (2009-09) Brunette, Katyarina Efimenko
    Using a dietary model in Sprague Dawley rats of gestational/neonatal iron deficiency, our lab has demonstrated structural, biochemical, electrophysiological and behavioral changes in the developing hippocampus. The high energy demands of the developing hippocampus make it particularly vulnerable to iron deficits. At gestational day two, the pregnant dams were given iron deficient (ID) chow to induce approximately 50 % brain iron deficiency by postnatal day (P)15. Our dietary model allowed us to observe changes during ID at P15 and P30 and also after iron repletion at P70. Dendritic changes have been demonstrated with MAP-2 staining, but this stain only allowed for measurement of the first portion of the apical dendrite. Therefore, the Golgi stain was used to allow for tracing of the entire apical dendritic trees, with quantification using Sholl analysis to observe the growth trajectory. The objective was to determine how apical dendrite growth is altered, short term and long term, by early iron deficiency. Approximately 20 neurons were traced from each of the three time points and two dietary conditions. Four or more animals were used from each group. Results show early iron deficiency altered dendritic developmental trajectory. Distance to peak branching was shorter in the ID and formerly ID animals as well as thinner third generation branches at P15. Also at P70 in FID animals, peak branching density was decreased. Decreased transcript levels were seen in the IDA and formerly IDA animals. Altered transcript levels of various cytoplasmic and transmembrane proteins critical to structural growth (RhoA, Rac1, Cdc42, Cypin, Cofillin, Profilin, Crmp1, Cxcr4) support altered morphology and contribute to reduced plasticity of the system. Early iron deficiency affects apical dendrite development and results in long term decreased cytoskeletal plasticity, these findings may underlie some of the functional deficits seen in this condition.
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    Early-Life Iron Deficiency Anemia Alters the Development and Long-Term Expression of Parvalbumin and Perineuronal Nets in the Rat Hippocampus
    (2015-06) Callahan, Liam
    Early-life iron deficiency anemia (IDA) alters the expression of genes involved in neuronal structural plasticity of the hippocampus, contributing to delayed maturation of electrophysiology, and learning and memory behavior in rats. Structural maturity in multiple cortical regions is characterized by the appearance of parvalbumin-positive (PV+) GABAergic interneurons and perineuronal nets (PNNs). Appearance of PV+ interneurons and PNNs serve as cellular markers for the beginning and end of a critical developmental period, respectively. ID rats had reduced PV mRNA expression and protein levels compared to IS controls. While there were no differences in the number of PV+ neurons at P30 or P65, the percentage of PV+ cells surrounded by PNNs was greater in ID rats as compared to IS controls. The alterations of these critical period biomarkers in the ID group are consistent with later maturation of the acutely ID hippocampus and lower plasticity in the adult formerly-ID hippocampus.
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    Modulation of hippocampal endocannabinoid plasticity by homer proteins and Delta(9)-tetrahydrocannabinol.
    (2009-10) Roloff, Alan Mathhew
    The endocannabinoid (eCB) system comprised of lipophylic signaling molecules, postsynaptic production enzymes, and presynaptic G-protein coupled receptors (GPCR) has recently emerged as a key mediator in a broad range of neuronal plasticity. Initial interest in the system stemmed from, delta(9)-tetrahydrocannabinol (THC) the main psychoactive ingredient in the illicit drug marijuana which elicits various effects on the central nervous system (CNS) through interactions with the eCB system. Further study described a nearly ubiquitous yet tunable system that may underlie many CNS functions. Studying the eCB system offers insight into the basic science of synaptic transmission but more importantly the mechanism by which postsynaptic determinants may influence their synaptic inputs to adapt to changing CNS conditions. The objective of these studies was to determine the properties of THC that dictate its relationship to the intact eCB system and to characterize how specific members of the homer family of postsynaptic scaffolding proteins impact differing forms of eCB-mediated plasticity. Activation of the cannabinoid receptor-1 (CB1R) by THC or eCBs leads to several presynaptic consequences, but most importantly to inhibition of voltage-gated calcium channels (VGCC) and thus a reduction of action potential induced neurotransmitter release. In the first study presented here, we described a voltage-mediated switch by which THC acts as an agonist of CB1R or as an antagonist to effects at CB1R mediated by eCBs. Using patch clamp electrophysiology to study excitatory synaptic transmission we discovered that the rate at which the presynaptic neuron is depolarized has drastic effects on THC mediated inhibition. Excitatory postsynaptic currents (EPSCs) evoked at 0.1 Hz were suppressed by THC, however THC did not effect EPSCs evoke at 0.5 Hz. Experiments using other CB1R agonists Win55212,2 (Win-2) and 2-Arachydonylglycerol (2-AG) did not demonstrate sensitivity to stimulus rate. THC application at 0.5 Hz stimulation antagonized the inhibition produced by Win-2. THC but not Win-2 inhibited influx of calcium through VGCCs in a rate dependent manner. Win-2 but not THC shifted the voltage-dependent activation of tail currents. THC but not Win-2 mediated inhibition of VGCCs displayed mild prepulse facilitation. THC antagonized depolarization-induced suppression of excitation (DSE). These findings illustrate the complex interplay between THC and the eCB system and suggest that behavioral responses to THC may stem from a combination of both CB1R activation and inhibition of eCB action at CB1R. Postsynaptic induction of the eCB system and subsequent production of eCBs may be achieved via several interrelated molecular mechanisms that focus around glutamatergic ionotropic and metabotropic signaling and postsynaptic intercellular Ca2+ concentration ([Ca2+]i). Homer, a family of postsynaptic scaffolding proteins, is present in the hippocampus and has been found to organize many of the structural and mechanistic proteins necessary for several forms of synaptic plasticity. In the second study we describe a homer isoform-specific switch in eCB plasticity that primes neurons for ionotropic mediated production of eCBs but shifts them away from metabotropic eCB production. Transfection of hippocampal cultures with homer 1a (H1a) enhances DSE. Transfection of cultures with H1a inhibits metabotropic suppression of excitation (MSE). In combination experiments on the same neuron with DSE followed by MSE, DSE is enhanced and MSE is inhibited in H1a expressing neurons. Brain derived neurotrophic factor (BDNF) induces formation of H1a mRNA and leads to functional expression of H1a which dissociates homer 1c-GFP puncta. BDNF mediates an enhancement of DSE and inhibition of MSE similar to that found in H1a transfected neurons. These findings identify H1a as a crucial mediator of eCB signaling that may be induced by BDNF and can lead to an enhancement of depolarization mediated eCB production. The second study delineated how postsynaptic homer proteins can influence differential paths to activating eCB mediated synaptic plasticity. The physiological manifestations of eCB signaling have tentacles that extend from neurotransmitter release to higher brain function through the regulation of Ca2+ channels and induction of synaptic plasticity. These studies are directed toward understanding the way in which THC interacts with the eCB system, and the postsynaptic scaffolding protein complement which induces changes to eCB-mediated plasticity. Delineating these concepts may lead to better understanding of higher brain function and will offer new targets for therapeutic development.