23,320 research outputs found

    Facilitatory actions of guanidine on synaptic transmission in mammalian brain slices

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    Guanidine administration may be beneficial in the treatment of amyotrophic lateral sclerosis and related diseases; however, the actions of guanidine on the mammalian central nervous system have not been investigated. We studied the effects of this compound on neuronal properties and synaptic transmission in isolated slices of guinea pig olfactory cortex using intra- and extracellular recording mothods. Addition of guanidine to the superfusate (≥300 μ ) produced the following effects. (a) Excitatory and inhibitory postsynaptic potentials, evoked by stimulation of the lateral olfactory tract, were increased in amplitude and duration; (b) the amplitude and frequency of spontaneously occurring postsynaptic potentials was significantly increased; (c) membrane potential and input resistance remained virtually unchanged; and (d) the duration of the lateral olfactory tract compound action potential was prolonged. These results suggest that guanidine enhances the release of excitatory and inhibitory neurotransmitters in the mammalian cortex and this effect may be beneficial in human central nervous system diseases in which the efficiency of synaptic transmission is reduced

    Method of making contamination-free ceramic bodies

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    Ceramic structures having high strength at temperatures above 1000 C after sintering are made by mixing ceramic powders with binder deflocculants such as guanidine salts of polymeric acids, guanidine salts of aliphatic organic carboxylic acids or guanidine alkylsulfates with the foregoing guanidine salts. The novelty of the invention appears to lie in the substitution of guanidine salts for the alkalai metal salt components or organic fatty acids of the prior art binder-deflocculant, ceramic processing aids whereby no undesirable metal contaminants are present in the final ceramic structure. Guanidine alkylsulfates also replace the Na or K alkylsulfates commonly used with binder-deflocculants in making high temperature ceramic structures

    Effects of guanidine on synaptic transmission in the spinal cord of the frog

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    The effects of guanidine on motoneurons of the isolated frog spinal cord were studied by adding the drug to the solution bathing the cord during intracellular recording. Guanidine (5·10–4 M) did not alter the membrane potential of motoneurons. The main effect was a marked increase of the amplitudes and frequencies of small spontaneously occurring inhibitory postsynaptic potentials. The hyperpolarizing component of postsynaptic potentials evoked by stimulation of dorsal roots was also enhanced by guanidine. Higher concentrations of guanidine (5·10–3 M) resulted in a very large and irreversible increase of the small spontaneously occurring inhibitory potentials, which now appeared in a regular, rhythmic pattern. The effects of guanidine could easily be blocked by increasing the magnesium ions (15 mM) in the bath solution. These results indicate that guanidine facilitates the release of an inhibitory transmitter in afferent terminals of the frog spinal cord either by a direct action on these terminals or indirectly by an action on nerve endings impinging on inhibitory interneurons

    Lethal Mutagenesis of Picornaviruses with N-6-Modified Purine Nucleoside Analogues

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    RNA viruses exhibit extraordinarily high mutation rates during genome replication. Nonnatural ribonucleosides that can increase the mutation rate of RNA viruses by acting as ambiguous substrates during replication have been explored as antiviral agents acting through lethal mutagenesis. We have synthesized novel N-6-substituted purine analogues with ambiguous incorporation characteristics due to tautomerization of the nucleobase. The most potent of these analogues reduced the titer of poliovirus (PV) and coxsackievirus (CVB3) over 1,000-fold during a single passage in HeLa cell culture, with an increase in transition mutation frequency up to 65-fold. Kinetic analysis of incorporation by the PV polymerase indicated that these analogues were templated ambiguously with increased efficiency compared to the known mutagenic nucleoside ribavirin. Notably, these nucleosides were not efficient substrates for cellular ribonucleotide reductase in vitro, suggesting that conversion to the deoxyriboucleoside may be hindered, potentially limiting genetic damage to the host cell. Furthermore, a high-fidelity PV variant (G64S) displayed resistance to the antiviral effect and mutagenic potential of these analogues. These purine nucleoside analogues represent promising lead compounds in the development of clinically useful antiviral therapies based on the strategy of lethal mutagenesis

    A monoclonal antibody that blocks the activity of a neurite regeneration-promoting factor: studies on the binding site and its localization in vivo

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    Work from several laboratories has identified a proteoglycan complex secreted by a variety of non-neuronal cells that can promote neurite regeneration when applied to the surface of culture dishes. Using a novel immunization protocol, a monoclonal antibody (INO) was produced that blocks the activity of this outgrowth-promoting factor (Matthew, W. D., and P. H. Patterson, 1983, Cold Spring Harbor Symp. Quant. Biol. 48:625-631). We have used the antibody to analyze the components of the active site and to localize the complex in vivo. INO binding is lost when the complex is dissociated; if its components are selectively reassociated, INO binds only to a complex containing two different molecular weight species. These are likely to be laminin and heparan sulfate proteoglycan, respectively. On frozen sections of adult rat tissues, INO binding is present on the surfaces of glial cells of the peripheral, but not the central, nervous system. INO also binds to the basement membrane surrounding cardiac and skeletal muscle cells, and binding to the latter greatly increases after denervation. In the adrenal gland and kidney, INO selectively reacts with areas rich in basement membranes, staining a subset of structures that are immunoreactive for both laminin and heparan sulfate proteoglycan. In general, the outgrowth-blocking antibody binds to areas known to promote axonal regeneration and is absent from areas known to lack this ability. This suggests that this complex, which is active in culture, may be the physiological substrate supporting nerve regeneration in vivo

    The formation of glycocyamine in animal tissues

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    It was shown in preceding communications that glycocyamine is converted into creatine by surviving liver slices (1). Our findings indicated that the methylating agent is methionine or a derivative of methionine. Liver slices can methylate glycocyamine rapidly enough to permit assignment to the liver alone, if necessary, of the task of making good the loss of creatine and creatinine in the urine. This holds for the livers of all mammals studied. We found no evidence of this methylating mechanism in any other tissues, except possibly slight activity in the kidney. In the pigeon the kidney is as effective in this respect as the liver

    Lethal Mutagenesis of Poliovirus Mediated by a Mutagenic Pyrimidine Analogue

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    Lethal mutagenesis is the mechanism of action of ribavirin against poliovirus (PV) and numerous other RNA viruses. However, there is still considerable debate regarding the mechanism of action of ribavirin against a variety of RNA viruses. Here we show by using T7 RNA polymerase mediated production of PV genomic RNA, PV polymerase-catalyzed primer extension and cell-free PV synthesis that a pyrimidine ribonucleoside triphosphate analogue (rPTP) with ambiguous basepairing capacity is an efficient mutagen of the PV genome. The in vitro incorporation properties of rPTP are superior to ribavirin triphosphate. We observed a log-linear relationship between virus titer reduction and the number of rPMP molecules incorporated. A PV genome encoding a high-fidelity polymerase was more sensitive to rPMP incorporation, consistent with diminished mutational robustness of high-fidelity PV. The nucleoside (rP) did not exhibit antiviral activity in cell culture owing to the inability of rP to be converted to rPMP by cellular nucleotide kinases. rP was also a poor substrate for herpes simplex virus thymidine kinase. The block to nucleoside phosphorylation could be bypassed by treatment with the P nucleobase, which exhibited both antiviral activity and mutagenesis, presumably a reflection of rP nucleotide formation by a nucleotide salvage pathway. These studies provide additional support for lethal mutagenesis as an antiviral strategy, suggest that rPMP prodrugs may be highly efficacious antiviral agents, and provide a new tool to determine the sensitivity of RNA virus genomes to mutagenesis as well as interrogation of the impact of mutational load on the population dynamics of these viruses

    A comprehensive evaluation of the activity and selectivity profile of ligands for RGD-binding integrins

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    Integrins, a diverse class of heterodimeric cell surface receptors, are key regulators of cell structure and behaviour, affecting cell morphology, proliferation, survival and differentiation. Consequently, mutations in specific integrins, or their deregulated expression, are associated with a variety of diseases. In the last decades, many integrin-specific ligands have been developed and used for modulation of integrin function in medical as well as biophysical studies. The IC50-values reported for these ligands strongly vary and are measured using different cell-based and cell-free systems. A systematic comparison of these values is of high importance for selecting the optimal ligands for given applications. In this study, we evaluate a wide range of ligands for their binding affinity towards the RGD-binding integrins avĂź3, avĂź5, avĂź6, avĂź8, a5Ăź1, aIIbĂź3, using homogenous ELISA-like solid phase binding assay.Postprint (published version
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