GLUTAMATE DYSREGULATION AND HIPPOCAMPAL DYSFUNCTION IN EPILEPTOGENESIS

Epileptogenesis is the complex process of the brain developing epileptic acitivity. Due to the role of glutamate and the hippocampus in synaptic plasticity a dysregulation in glutamate neurotransmission and hippocampal dysfunction are implicated in the process of epileptogenesis. However, the exact causal factors that promote epileptogenesis are unknown. We study presynaptic proteins that regulate glutamate neurotransmission and their role in epileptogenesis. The presynaptic protein, tomosyn, is believed to be a negative regulator of glutamate neurotransmission; however, no one has studied the effects of this protein on glutamate transmission in vivo. Furthermore, evidence suggests that mice lacking tomosyn have a kindling phenotype. Thus, in vivo glutamate recordings in mice lacking tomosyn have the potential to elucidate the exact role of tomosyn in glutamate neurotransmission and its potential relationship to epileptogenesis. Here we used biosensors to measure glutamate in the dentate gyrus (DG), CA3, and CA1 of the hippocampus in tomosyn wild-type (Tom+/+), heterozygous (Tom+/-), and knock out (Tom-/-) mice. We found that, in the DG, that glutamate release increases as tomosyn expression decreases across genotype. This suggests that tomosyn dysregulation in the DG leads to an increase in glutamate release, which may explain why these mice have an epileptogenic phenotype

Linking Kindling to Increased Glutamate Release in the Dentate Gyrus of the Hippocampus Through the STXBP5/tomosyn-1 Gene

Introduction: In kindling, repeated electrical stimulation of certain brain areas causes progressive and permanent intensification of epileptiform activity resulting in generalized seizures. We focused on the role(s) of glutamate and a negative regulator of glutamate release, STXBP5/tomosyn-1, in kindling. Methods: Stimulating electrodes were implanted in the amygdala and progression to two successive Racine stage 5 seizures was measured in wild-type and STXBP5/tomosyn-1−/− (Tom−/−) animals. Glutamate release measurements were performed in distinct brain regions using a glutamate-selective microelectrode array (MEA). Results: Naïve Tom−/− mice had significant increases in KCl-evoked glutamate release compared to naïve wild type as measured by MEA of presynaptic release in the hippocampal dentate gyrus (DG). Kindling progression was considerably accelerated in Tom−/− mice, requiring fewer stimuli to reach a fully kindled state. Following full kindling, MEA measurements of both kindled Tom+/+ and Tom−/− mice showed significant increases in KCl-evoked and spontaneous glutamate release in the DG, indicating a correlation with the fully kindled state independent of genotype. Resting glutamate levels in all hippocampal subregions were significantly lower in the kindled Tom−/−mice, suggesting possible changes in basal control of glutamate circuitry in the kindled Tom−/−mice. Conclusions: Our studies demonstrate that increased glutamate release in the hippocampal DG correlates with acceleration of the kindling process. Although STXBP5/tomosyn-1 loss increased evoked glutamate release in naïve animals contributing to their prokindling phenotype, the kindling process can override any attenuating effect of STXBP5/tomosyn-1. Loss of this “braking” effect of STXBP5/tomosyn-1 on kindling progression may set in motion an alternative but ultimately equally ineffective compensatory response, detected here as reduced basal glutamate release

Calcineurin/NFAT Signaling in Activated Astrocytes Drives Network Hyperexcitability in A\u3cem\u3eβ\u3c/em\u3e-Bearing Mice

Hyperexcitable neuronal networks are mechanistically linked to the pathologic and clinical features of Alzheimer\u27s disease (AD). Astrocytes are a primary defense against hyperexcitability, but their functional phenotype during AD is poorly understood. Here, we found that activated astrocytes in the 5xFAD mouse model were strongly associated with proteolysis of the protein phosphatase calcineurin (CN) and the elevated expression of the CN-dependent transcription factor nuclear factor of activated T cells 4 (NFAT4). Intrahippocampal injections of adeno-associated virus vectors containing the astrocyte-specific promoter Gfa2 and the NFAT inhibitory peptide VIVIT reduced signs of glutamate-mediated hyperexcitability in 5xFAD mice, measured in vivo with microelectrode arrays and ex vivo brain slices, using whole-cell voltage clamp. VIVIT treatment in 5xFAD mice led to increased expression of the astrocytic glutamate transporter GLT-1 and to attenuated changes in dendrite morphology, synaptic strength, and NMDAR-dependent responses. The results reveal astrocytic CN/NFAT4 as a key pathologic mechanism for driving glutamate dysregulation and neuronal hyperactivity during AD

P301L tau expression affects glutamate release and clearance in the hippocampal trisynaptic pathway

Individuals at risk of developing Alzheimer’s disease (AD) often exhibit hippocampal hyperexcitability. A growing body of evidence suggests perturbations in the glutamatergic tripartite synapse may underlie this hyperexcitability. Here, we used a tau mouse model of AD (rTg(TauP301L)4510) to examine the effects of tau pathology on hippocampal glutamate regulation. We found a 40% increase in hippocampal vGLUT, which packages glutamate into vesicles, and has previously been shown to influence glutamate release, and a 40% decrease in hippocampal GLT-1, the major glutamate transporter responsible for removing glutamate from the extracellular space. To determine whether these alterations affected glutamate regulation in vivo, we measured tonic glutamate levels, potassium-evoked glutamate release, and glutamate uptake/clearance in the dentate gyrus (DG), CA3, and CA1 regions of the hippocampus. P301L tau expression resulted in a 4- and 7-fold increase in potassium-evoked glutamate release in the DG and CA3, respectively, and significantly decreased glutamate clearance in all 3 regions. Both release and clearance correlated with memory performance in the hippocampal-dependent Barnes maze task. Alterations in mice expressing P301L were observed at a time when tau pathology was subtle and before readily detectable neuron loss. These data suggest novel mechanisms by which tau may mediate hyperexcitability

Deconstruction of Crystalline Networks into Underlying Nets: Relevance for Terminology Guidelines and Crystallographic Databases

This communication briefly reviews why network topology is an important tool (for understanding, comparing, communicating, designing, and solving crystal structures from powder diffraction data) and then discusses the terms of an IUPAC project dealing with various aspects of network topology. One is the ambiguity in node assignment, and this question is addressed in more detail. First, we define the most important approaches: the "all node" deconstruction considering all branch points of the linkers, the "single node" deconstruction considering only components mixed, and the ToposPro "standard representation" also considering linkers as one node but, if present, takes each metal atom as a separate node. These methods are applied to a number of metal organic framework structures (MOFs, although this is just one example of materials this method is applicable on), and it is concluded that the "all node" method potentially yields more information on the structure in question but cannot be recommended as the only way of reporting the network topology. In addition, several terms needing definitions are discussed

Straining and relaxation properties of wet paper during heating

The influence of increasing temperature on the strength and relaxation of wet press-dry paper was studied using a tensile tester equipped with a special heating chamber. The heating chamber made fast heating possible without detectable moisture loss. The results showed that temperature had a significant influence on the straining, relaxation and re-straining behavior of wet paper. The majority of observed changes due to increased temperature seem to originate from the softening of wet fibers. The observed short time scale phenomena in wet paper have practical significance for fiber webs dried under tension in paper machines. Straining–relaxation–de-straining cycles were used to analyze the effect of heating on the work of straining and apparent plastic and elastic work. Heating affected the amount of mechanical energy absorbed by the sample and the amount of elastic energy recoverable in a straining–relaxation–de-straining cycle. Increased temperature reduced the work of straining and both elastically and plastically absorbed energy. The hysteresis work of the examined wet papers was estimated to correspond to a 1–22 mK temperature change. This suggests that temperature changes in wet paper induced by straining play no role in practice. After mechanical conditioning, tensile stiffness in the re-straining of wet paper depended only marginally on temperature, whereas in initial straining the effect of temperature was clearly stronger. The linear thermal expansion coefficient of wet paper in the machine direction was estimated and the influence of moisture content on the linear thermal expansion coefficient of paper was found to be relatively small