Tetrahydrobiopterin deficiency and brain nitric oxide metabolism

Tetrahydrobiopterin is an essential cofactor for the aromatic amino acid monooxygenase group of enzymes. Inborn errors of tetrahydrobiopterin metabolism result in hyperphenylalaninaemia and impaired catecholamine and serotonin turnover. Tetrahydrobiopterin is also a cofactor for all known isoforms of nitric oxide synthase (NOS). The effect of tetrahydrobiopterin deficiency on brain nitric oxide metabolism has to date been given little consideration. In this thesis the effect of tetrahydrobiopterin deficiency on brain nitric oxide metabolism has been studied using a mouse model of tetrahydrobiopterin deficiency, the hph-1 mouse. Tetrahydrobiopterin was measured in 10 and 30 day old mice in whole brain and cerebellum. At both age points there was a significant -50% reduction in tetrahydrobiopterin content for whole brain and cerebellum in the hph-1 mouse compared to corresponding control mice. NOS activity was measured in whole brain from 10 and 30 day old hph-1 and control mice. No difference was observed in enzyme activity when tetrahydrobiopterin was included in the incubation medium. However, omission of tetrahydrobiopterin from the reaction buffer resulted in significantly lower NOS activity in the hph-1 mouse group compared to controls. Tetrahy-drobiopterin was also shown to have a potent effect on the affinity of brain NOS for arginine. The Km for arginine was virtually identical for the control and hph-1 mouse when tetrahydrobiopterin was included in the reaction buffer. In the absence of cofactor, the for arginine was three fold greater for control and five fold higher for hph-1 preparations. The accumulation of cGMP from slices prepared from the cerebellum was measured in both groups of mice at both 10 and 30 days using the glutamate analogue, kainate. In the 10 day old hph-1 mouse there was a significant 50% reduction in cGMP levels under basal and stimulated conditions. In the 30 day old hph-1 mouse there was a significant 30% reduction in cGMP accumulation in both basal and activated states. Whole brain amino acid levels were measured. In the 10 day old hph-1 mouse confounding hyperphenylalaninaemia may affect the availability of the NOS substrate, arginine. In the 30 day old hph-1 mouse, which has normal phenylalanine levels, reduced citrulline levels may indicate reduced NOS activity. Reduced levels of tetrahydrobiopterin and also arginine, have been shown to lead to superoxide formation by nitric oxide synthase. Superoxide can react with nitric oxide to form the oxidising species, peroxynitrite, which has been shown to damage of the mitochondrial electron transport chain. Mitochondrial function together with the antioxidant, glutathione, were analysed in both hph-1 and control mice at 10 and 30 days to measure oxidative stress. However, no differences were observed between the two groups. In summary, partial deficiency of tetrahydrobiopterin appears to lead to impaired brain NOS function leading to an impairment of the nitric oxide/cGMP pathway

Shocked H2 and Fe+ Dynamics in the Orion Bullets

Observations of H2 velocity profiles in the two most clearly defined Orion bullets are extremely difficult to reconcile with existing steady-state shock models. We have observed [FeII] 1.644um velocity profiles of selected bullets and H2 1-0 S(1) 2.122um velocity profiles for a series of positions along and across the corresponding bow-shaped shock fronts driven into the surrounding molecular cloud. Integrated [FeII] velocity profiles of the brightest bullets are consistent with theoretical bow shock predictions. However, observations of broad, singly-peaked H2 1-0 S(1) profiles at a range of positions within the most clearly resolved bullet wakes are not consistent with molecular shock modelling. A uniform, collisionally broadened background component which pervades the region in both tracers is inconsistent with fluorescence due to the ionizing radiation of the Trapezium stars alone.Comment: 20 pages including 18 figures, published in MNRA

Assembly dynamics of PML nuclear bodies in living cells

The mammalian cell nucleus contains a variety of organelles or nuclear bodies which contribute to key nuclear functions. Promyelocytic leukemia nuclear bodies (PML NBs) are involved in the regulation of apoptosis, antiviral responses, the DNA damage response and chromatin structure, but their precise biochemical function in these nuclear pathways is unknown. One strategy to tackle this problem is to assess the biophysical properties of the component parts of these macromolecular assemblies in living cells. In this study we determined PML NB assembly dynamics by live cell imaging, combined with mathematical modeling. For the first time, dynamics of PML body formation were measured in cells lacking endogenous PML. We show that all six human nuclear PML isoforms are able to form nuclear bodies in PML negative cells. All isoforms exhibit individual exchange rates at NBs in PML positive cells but PML I, II, III and IV are static at nuclear bodies in PML negative cells, suggesting that these isoforms require additional protein partners for efficient exchange. PML V turns over at PML Nbs very slowly supporting the idea of a structural function for this isoform. We also demonstrate that SUMOylation of PML at Lysine positions K160 and/or K490 are required for nuclear body formation in vivo.We propose a model in which the isoform specific residence times of PML provide both, structural stability to function as a scaffold and flexibility to attract specific nuclear proteins for efficient biochemical reactions at the surface of nuclear bodies

Aerial Cable-car Systems for Public Transport in Low-income Urban Areas: Lessons from Medellin, Colombia

In 2004 the first urban aerial cable-car public transport system was introduced in the city of Medellín, Colombia. The imaginative application of ski-slope technology to high-gradient, low-income urban areas attracted widespread attention from city authorities throughout Latin America, as well as Europe and Asia. However a second cable introduced in 2008 has had far less impact, confirming the suspicion that, to be worthwhile, cable-car systems require specific minimum conditions in terms of urban morphology and population density, as well as concerted complementary action by city authorities in order to ensure that mobility benefits help improve the living conditions, economic opportunities and social inclusion of the affected area populations. This paper outlines the technical and financial aspects of the cable-car systems employed in Medellin, and examines the urban conditions and planning considerations required to ensure the full integration and maximisation of social, economic and political benefits for catchment area populations, and provides pointers to successful application in other cities of the world

Evaluation of image tubes in astronomy

It is to be hoped that the methods described in the first part of this thesis will be extensively applied to imaging devices and to photographic emulsions, since this is the only way in which an unambiguous figure for the performance of the detector may be derived. Lack of attention to such concepts has produced many pitfalls, notably the enormous (and imaginary) gains reported earlier for various types of image tube, which, when they were not realised in practice, produced some considerable despondency.The work of Shaw(60) on aerial films is an out- standing example of thorough application of Information Theory to the photographic process. His results are formally the same as those of Chapter I of this thesis.The results derived enable a prediction of signal-to-noise-ratio (accuracy) and information gain for the image tube under any conditions of exposure. The results also point to the necessity of knowing, for instance, the IMF of the spectrograph used with the detector, in order to fully exploit the storage capacity of the detector.Part II of this work has described the manner in which the Spectracon, as a particular example of an astronomical image tube, may be brought into routine use as part of the observational astronomer's instrument capability.Much is still to be achieved in this field. In particular, the emulsions are in no way comparable in standard (understandably, they are still a laboratory - rather than commercial - commodity) with the best astronomical emulsions. Similarly, such is the experimental complexity in building a tube, that to produce a flawless cathode and window ( and both are focal surfaces) is asking a great deal. But it is not asking for the impossible, and it is foreseeable that in time such difficulties will be eliminated.There remains the problem of the small area of the cathode. In effect, while the information storage capacity of the image tube is considerably greater than that of astronomical emulsions, its limited area rather nullifies this advantage in that, with suitable coding, all the information in the small cathode area could be spread onto one large astronomical plate. However, to do this the exposing intensity must be reduced, and this, because of the nonlinearity of the photographic process, reduces the efficiency.Thus the crucial advantage in using an image tube must be in exploiting its higher detecting efficiency. If programs consist in looking at small regions of spectrum (or of sky), then the advantages of the image tube are obvious. Some of this work has already been reported in a paper read to the 3rd Symposium on Photoelectronic Imaging Devices

Instructional Support for Enhancing Students’ Information Problem Solving Ability

Brand-Gruwel, S., & Gerjets, P. (Eds.). (2008). Instructional Support for Enhancing Students’ Information Problem Solving Ability [Special issue]. Computers in Human Behavior, 24(3).This special issue discusses European research on instructional support to foster students’ ability to solve information-based problems. In this introduction, the concept of information problem solving (IPS) and research in this field of interest will be placed in the broader perspective, which is called information behavior. The focus of this special issue is an educational one and the papers all go into a specific kind of instructional support. The main research questions, findings and conclusions of the six contributions will be outlined. It is concluded that the most important directions for future research deal with how instructional support for different aspect of the process, like for instance how to regulated the process, best can be designed in order to make the instruction adaptive and fit to the learners needs