Depolarization-activated potentiation of the T fiber synapse in the blue crab

The blue crab T fiber synapse, associated with the stretch receptor of the swimming leg, has a nonspiking presynaptic element that mediates tonic transmission. This synapse was isolated and a voltage clamp circuit was used to control the membrane potential at the release sites. The dependence of transmitter release on extracellular calcium, [Ca]o, was studied over a range of 2.5-40 mM. A power relationship of 2.7 was obtained between excitatory postsynaptic potential (EPSP) rate of rise and [Ca]o. Brief presynaptic depolarizing steps, 5-10 ms, presented at 0.5 Hz activated EPSP's of constant amplitude. Inserting a 300-ms pulse (conditioning pulse) between these test pulses potentiated the subsequent test EPSPs. This depolarization-activated potentiation (DAP) lasted for 10-20 s and decayed with a single exponential time course. The decay time course remained invariant with test pulse frequencies ranging from 0.11 to 1.1 Hz. The magnitude and decay time course of DAP were independent of the test pulse amplitudes. The magnitude of DAP was a function of conditioning pulse amplitudes. Large conditioning pulses activated large potentiations, whereas the decay time constants were not changed. The DAP is a Ca-dependent process. When the amplitude of conditioning pulses approached the Ca equilibrium potential, the magnitude of potentiation decreased. Repeated application of conditioning pulses, at 2-s intervals, did not produce additional potentiation beyond the level activated by the first conditioning pulse. Comparison of the conditioning EPSP waveforms activated repetitively indicated that potentiation lasted transiently, 100 ms, during a prolonged release. Possible mechanisms of the potentiation are discussed in light of these new findings.The blue crab T fiber synapse, associated with the stretch receptor of the swimming leg, has a nonspiking presynaptic element that mediates tonic transmission. This synapse was isolated and a voltage clamp circuit was used to control the membrane potential at the release sites. The dependence of transmitter release on extracellular calcium, [Ca]o, was studied over a range of 2.5-40 mM. A power relationship of 2.7 was obtained between excitatory postsynaptic potential (EPSP) rate of rise and [Ca]o. Brief presynaptic depolarizing steps, 5-10 ms, presented at 0.5 Hz activated EPSP's of constant amplitude. Inserting a 300-ms pulse (conditioning pulse) between these test pulses potentiated the subsequent test EPSPs. This depolarization-activated potentiation (DAP) lasted for 10-20 s and decayed with a single exponential time course. The decay time course remained invariant with test pulse frequencies ranging from 0.11 to 1.1 Hz. The magnitude and decay time course of DAP were independent of the test pulse amplitudes. The magnitude of DAP was a function of conditioning pulse amplitudes. Large conditioning pulses activated large potentiations, whereas the decay time constants were not changed. The DAP is a Ca-dependent process. When the amplitude of conditioning pulses approached the Ca equilibrium potential, the magnitude of potentiation decreased. Repeated application of conditioning pulses, at 2-s intervals, did not produce additional potentiation beyond the level activated by the first conditioning pulse. Comparison of the conditioning EPSP waveforms activated repetitively indicated that potentiation lasted transiently, 100 ms, during a prolonged release. Possible mechanisms of the potentiation are discussed in light of these new findings.NS-07942 - NINDS NIH HHS; NS-13742 - NINDS NIH HH

Temperature and density measurements in the base region of a clustered rocket model using an electron beam technique

Temperature and density measurements in base region flow field of clustered rocket engine model using electron beam techniqu

Plasmodium falciparum glutamate dehydrogenase a is dispensable and not a drug target during erythrocytic development

<p>Background: Plasmodium falciparum contains three genes encoding potential glutamate dehydrogenases. The protein encoded by gdha has previously been biochemically and structurally characterized. It was suggested that it is important for the supply of reducing equivalents during intra-erythrocytic development of Plasmodium and, therefore, a suitable drug target.</p> <p>Methods: The gene encoding the NADP(H)-dependent GDHa has been disrupted by reverse genetics in P. falciparum and the effect on the antioxidant and metabolic capacities of the resulting mutant parasites was investigated.</p> <p>Results: No growth defect under low and elevated oxygen tension, no up-or down-regulation of a number of antioxidant and NADP(H)-generating proteins or mRNAs and no increased levels of GSH were detected in the D10(Delta gdha) parasite lines. Further, the fate of the carbon skeleton of [(13)C] labelled glutamine was assessed by metabolomic studies, revealing no differences in the labelling of a-ketoglutarate and other TCA pathway intermediates between wild type and mutant parasites.</p> <p>Conclusions: First, the data support the conclusion that D10(Delta gdha) parasites are not experiencing enhanced oxidative stress and that GDHa function may not be the provision of NADP(H) for reductive reactions. Second, the results imply that the cytosolic, NADP(H)-dependent GDHa protein is not involved in the oxidative deamination of glutamate but that the protein may play a role in ammonia assimilation as has been described for other NADP(H)dependent GDH from plants and fungi. The lack of an obvious phenotype in the absence of GDHa may point to a regulatory role of the protein providing glutamate (as nitrogen storage molecule) in situations where the parasites experience a limiting supply of carbon sources and, therefore, under in vitro conditions the enzyme is unlikely to be of significant importance. The data imply that the protein is not a suitable target for future drug development against intra-erythrocytic parasite development.</p&gt

A Scale Model Investigation of Rocket Exhaust Effects on an Improved Saturn V Booster Utilizing Solid Propellant Strap-Ons

Missions currently being considered by NASA beyond the Apollo manned lunar landing will require a larger payload capability than is available with the current generation of Saturn boosters. An attractive method of achieving the desired payload increase consists of adding large solid propellant rocket motors (strap-ons) to existing boosters to augment the thrust from the basic booster liquidpropellant engines. The soundness of this approach has already been demonstrated by such vehicles as the Titan III-C and Thrust Augmented Thor/Delta, where significant performance increases have been obtained within current state of the art and at minimum cost, while simultaneously retaining the proven reliability characteristics of the previously developed basic booster. The possibility of increasing the performance of the Saturn V booster through the addition of previously developed 120-inch solid-propellant rochet motor strap-ons to the S-IC first stage is currently being evaluated by the Marshall Space Flight Center of NASA. One of the items of concern with such a configuration is the possibility of a detrimental alteration in the base environment of the S-IC from that which will exist with only the basic complement of five F-l liquid propellant rockets. For example, interactions between the liquid propellant and/or solid propellant rocket exhaust plumes (a total of nine rocket exhausts are involved) may result in increased flow recirculation and attendant increases in base pressure and convective heating. Further, radiant heating to the base may also be significantly greater because of the presence of the aluminized solid propellant exhaust plumes. In addition to these potential flight problems, consideration must also be directed toward the launch stand environment. Rocket exhaust recirculation from the flame deflector can produce a severe thermal environment in the booster base region during the ignition and lift-off sequence, Launch stand components must also be suitably protected to withstand the 5000 °F exhaust gas impingement as the booster lifts off

The activities of protein kinase CK2 in oogenesis of `Xenopus laevis'

Protein kinases play important roles in regulating cellular functions in many organisms. This work deals specifically with the protein kinase CK2 (casein kinase II) and its role in regulating the activity of proteins involved in oocyte development in Xenopus laevis. Protein kinase CK2 is a tetrameric enzyme containing two catalytic subunits (alpha and alpha') and two identical regulatory subunits (beta) which forms the holoenzyme. CK2 phosphorylates many different proteins involved in many aspects of cellular functions. It phosphorylates serine and threonine sites and is considered to be a ubiquitous enzyme, expressed at different levels in different cell types. In this study CK2 activity was characterized in material from two sources: from isolated nuclei and messenger ribonucleoprotein (mRNP) particles from Xenopus oocytes. cDNAs expressing both the alpha and the beta subunits were cloned and antibodies were raised against the fusion protein containing the beta-subunit. The main objective of this study was to determine the effects that CK2 had on proteins involved in oocyte development. The interaction of CK2 with a protein known as histone deacetylase was studied in depth to determine how phosphorylation might influence its function and cellular compartmentalisation. Specifically, phosphorylation by CK2 is shown to improve the kinetics of nuclear unport, and the interaction of histone deacetylase with alpha-importin, a well-established nuclear transport protein, is revealed to be dependent on the phosphorylation state of histone deacetylase. Another aspect of this work is related to the association of CK2 with mRNP particles in the cytoplasm. mRNP particles function as long term storage units for mRNA to be used during oocyte maturation and early embryogenesis. It has been postulated that a protein kinase associated with these particles plays a role in controlling the binding of mRNA to proteins involved in translation repression (mRNA masking proteins). This study lends support to that theory, and the possible effects of CK2 phosphorylation on the masking "Y-box" proteins are discussed

Stimulus - response curves of a neuronal model for noisy subthreshold oscillations and related spike generation

We investigate the stimulus-dependent tuning properties of a noisy ionic conductance model for intrinsic subthreshold oscillations in membrane potential and associated spike generation. On depolarization by an applied current, the model exhibits subthreshold oscillatory activity with occasional spike generation when oscillations reach the spike threshold. We consider how the amount of applied current, the noise intensity, variation of maximum conductance values and scaling to different temperature ranges alter the responses of the model with respect to voltage traces, interspike intervals and their statistics and the mean spike frequency curves. We demonstrate that subthreshold oscillatory neurons in the presence of noise can sensitively and also selectively be tuned by stimulus-dependent variation of model parameters.Comment: 19 pages, 7 figure

Cross-continental emergence of Nannizziopsis barbatae disease may threaten wild Australian lizards

Members of the genus Nannizziopsis are emerging fungal pathogens of reptiles that have been documented as the cause of fatal mycoses in a wide range of reptiles in captivity. Cases of severe, proliferative dermatitis, debility and death have been detected in multiple free-living lizard species from locations across Australia, including a substantial outbreak among Eastern water dragons (Intellagama lesueurii) in Brisbane, Queensland. We investigated this disease in a subset of severely affected lizards and identified a clinically consistent syndrome characterized by hyperkeratosis, epidermal hyperplasia, dermal inflammation, necrosis, ulceration, and emaciation. Using a novel fungal isolation method, histopathology, and molecular techniques, we identified the etiologic agent as Nannizziopsis barbatae, a species reported only once previously from captive lizards in Australia. Here we report severe dermatomycosis caused by N. barbatae in five species of Australian lizard, representing the first cases of Nannizziopsis infection among free-living reptiles, globally. Further, we evaluate key pathogen and host characteristics that indicate N. barbatae-associated dermatomycosis may pose a concerning threat to Australian lizards