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In vivo MRS is a non-invasive measurement technique used not only in humans, but also in animal models using high-field magnets. MRS enables the measurement of metabolite concentrations as well as metabolic rates and their modifications in healthy animals and disease models. Such data open the way to a deeper understanding of the underlying biochemistry, related disturbances and mechanisms taking place during or prior to symptoms and tissue changes. In this work, we focus on the main preclinical (1)H, (31)P and (13)C MRS approaches to study brain metabolism in rodent models, with the aim of providing general experts’ consensus recommendations (animal models, anesthesia, data acquisition protocols). An overview of the main practical differences in preclinical compared with clinical MRS studies is presented, as well as the additional biochemical information that can be obtained in animal models in terms of metabolite concentrations and metabolic flux measurements. The properties of high-field preclinical MRS and the technical limitations are also described.

The ability to avoid blue-light radiation is crucial for bacteria to survive. In Halorhodospira halophila, the putative receptor for this response is known as photoactive yellow protein (PYP). Its response to blue light is mediated by changes in the optical properties of the chromophore para-coumaric acid (pCA) in the protein active site. PYP displays photocycle kinetics with a strong pH dependence for ground-state recovery, which has remained enigmatic. To resolve this problem, a comprehensive pK(a) determination of the active-site residues of PYP is required. Herein, we show that Glu-46 stays protonated from pH 3.4 to pH 11.4 in the ground (pG) state. This conclusion is supported by the observed hydrogen-bonded protons between Glu-46 and pCA and Tyr-42 and pCA, which are persistent over the entire pH range. Our experimental results show that none of the active-site residues of PYP undergo pH-induced changes in the pG state. Ineluctably, the pH dependence of pG recovery is linked to conformational change that is dependent upon the population of the relevant protonation state of Glu-46 and the pCA chromophore in the excited state, collaterally explaining why pG recovery is slow.

Quantity and quality of soil organic matter (SOM) affect physical, chemical, and biological soil properties, and are pivotal to productive and healthy grasslands. Thus, we analyzed the distribution of soil aggregates and assessed quality, quantity, and distribution of SOM in two unimproved and improved (two organic and two conventional) grasslands in subarctic Iceland, in Haplic and Histic Andosols. We also evaluated principal physicochemical and biological soil properties, which influence soil aggregation and SOM dynamics. Macroaggregates (>250 µm) in topsoils were most prominent in unimproved (62–77%) and organically (58–69%) managed sites, whereas 20–250 µm aggregates were the most prominent in conventionally managed sites (51–53%). Macroaggregate stability in topsoils, measured as mean weight diameter, was approximately twice as high in organically managed (12–20 mm) compared with the conventionally managed (5–8 mm) sites, possibly due to higher organic inputs (e.g., manure, compost, and cattle urine). In unimproved grasslands and one organic site, macroaggregates contributed between 40% and 70% of soil organic carbon (SOC) and nitrogen to bulk soil, whereas in high SOM concentration sites free particulate organic matter contributed up to 70% of the SOC and nitrogen to bulk soil. Aggregate hierarchy in Haplic Andosols was confirmed by different stabilizing mechanisms of micro- and macroaggregates, however, somewhat diminished by oxides (pyrophosphate-, oxalate-, and dithionite-extractable Fe, Al, and Mn) acting as binding agents for macroaggregates. In Histic Andosols, no aggregate hierarchy was observed. The higher macroaggregate stability in organic farming practice compared with conventional farming is of interest due to the importance of macroaggregates in protecting SOM and soils from erosion, which is a prerequisite for soil functions in grasslands that are envisaged for food production in the future.

A method for in vivo carbon-edited detection with proton echo-planar spectroscopic imaging (ICED PEPSI) is described. This method is composed of an echo-planar based acquisition implemented with C-13-H-1 J editing spectroscopy and is intended for high temporal and spatial resolution in vivo spectroscopic imaging of C-13 turnover, from D-[1,6-C-13]glucose to glutamate and glutamine, in the brain. At a static magnetic field strength of 7 T, both in vitro and in vivo chemical shift imaging data are presented with a spatial resolution of 8 mu L (i.e., 1.25 x 1.25 x 5.00 mm(3)) and a maximum spectral bandwidth of 5.2 ppm in H-1. Chemical shift imaging data acquired every 11 minutes allowed detection of regional [4-(CH2)-C-13]glutamate turnover in rat brain. The [4-(CH2)-C-13]glutamate turnover curves, which can be converted to tricarboxylic acid cycle fluxes, showed that the tricarboxylic acid cycle flux (V-TCA) in pure gray and white matter can range from 1.2 +/- 0.2 to 0.5 +/- 0.1 mu mol/g/min, respectively, for morphine-anesthetized rats. The mean cortical V-TCA from 32 voxels of 1.0 +/- 0.3 mu mol/g/min (N = 3) is in excellent agreement with previous localized measurements that have demonstrated that V-TCA can range from 0.9-1.1 mu mol/g/min under identical anesthetized conditions. (C) 1999 Wiley-Liss, Inc.

[1] Fire-derived black carbon (BC: charcoal and soot) has been thought to be a passive player in soils, contributing to the refractory soil organic carbon (SOC) pool, but playing no role in pedogenesis and regional short-term carbon cycling. This model, however, is at odds with recent results on the role of charcoal in soil fertility and its detection in the dissolved organic carbon (DOC) pool. For example, if BC simply accumulated passively in soils, its pattern of accumulation should match a simple model correlating fire frequency to BC storage. Instead, soil type, climate, biota, and land use practices all appear to play roles in controlling whether BC accumulates or is lost from soils. We summarize current knowledge of BC-soil interactions and construct a new paradigm describing the controls on BC storage in soils. We reconcile the refractory-labile BC paradox by proposing a model where BC storage is controlled by (1) fire frequency, (2) ecosystem presence or absence of aromatic precursor carbon and appropriate combustion conditions, (3) biological or physical mixing to remove BC from the soil surface, where it is vulnerable to combustion in future fires, (4) the presence or absence of soil mineral fractions able to sorb BC into the long-term stable carbon pool, and (5) the presence of microbial communities capable of degrading aromatic carbon. We also recognize that soil BC/SOC ratios are strongly influenced by land-use practices and add (6) human activities as a final control.

Soil organic matter (SOM) in allophanic soils is supposed to accumulate due to protection caused by binding to allophane, aluminium and iron. We investigated a catena of allophanic and non-allophanic soils in Costa Rica to determine the effect of such binding mechanisms on SOM chemistry. These soils contain no contribution of black carbon. Molecular characterization of litter, extractable and dispersed organic matter was done by Curie-point pyrolysis-GC/MS. The molecular chemistry of the organic fractions indicates a strong decomposition of plant-derived organic matter and a strong contribution of microbial sugars and N-compounds to SOM. Both the decomposition of plant-derived SOM ¿ including that of relatively recalcitrant compounds ¿ and the relative contribution of microbial SOM were greater in allophanic samples than in non-allophanic ones. This suggests that chemical protection does not act on primary OM, although it may influence the accumulation of secondary OM in these soils. The effect of allophane on SOM contents in such perhumid soils is probably through incorporation of decomposition products and microbial SOM in very fine aggregates that ¿ in a perhumid environment ¿ remain saturated with water during much of the year. Greater concentrations of aliphatics are found in allophanic residues, but there is no evidence of any specific mineral-organic binding. The results do not support the existing theory of chemical protection of plant-derived components through binding to allophane, iron and aluminium.

NaOH and Na4P2O7 extractable organic matter fractions of two volcanic ash profiles (Azores Islands) were studied by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). The soils did not have melanic horizons and were not affected by burning. The pyrolysates of all samples were dominated by polysaccharide-derived compounds. The Na4P2O7 extractable fractions were relatively enriched by markers of lignin, proteins, and lipids. Only in the topsoils (A horizons) did lignin appear to be present in significant amounts and, although present with a high degree of side-chain oxidation, the distribution of lignin-derived products could be related to the overlying vegetation. A similar trend was observed for lipids, in particular the high abundance of C26 alkanol in profile EUR05 clearly reflecting grass. Below the topsoils, lignin and lipids were hardly detectable. With depth, markers of intact polysaccharides decreased relatively to smaller polysaccharide pyrolysis products. The same is true for chitin. Compared with other soils, the relative abundance of lignin and lipids was remarkably low. The occurrence of large amounts of polysaccharides including chitin points to an important in situ production of soil organic matter by fungi and/or arthropods. There is no indication of preservation of plant-derived organic matter by allophane or Al3+, but the presence of large amounts of (microbial) polysaccharides and chitin suggests that these secondary organic matter products are indeed stabilized.

To gain understanding about the process of global warming, it is essential to study the global C cycle. In the global C cycle, soil organic matter (SOM) is a major source and sink of atmospheric C. Turnover times of C in these soil organic compounds vary from hours to thousands of years. Clay minerals can stabilize SOM through the formation of organo-mineral bonds. The aim of this research was first, to determine the mean residence time (MRT) of organic matter that is bound to different clay mineral surfaces, and second, to explain the variance in the measured MRTs using multilinear regression. We especially studied organic matter that is bound to kaolinite or smectite. We analyzed the 14C activity of organic matter in the whole and heavy clay-size fraction of kaolinite- and smectite-dominated soils from N'Ropa, in northern Mozambique. The soils originated from natural savanna systems and bamboo forest. We assumed that C inputs and outputs are in equilibrium in such soils, so that the 14C age equals the MRT of the organic C. For both kaolinite- and smectite-dominated soils, the organic matter in the whole and heavy clay-size fraction and extracts had a fast turnover (400¿500 yr on average). The MRT of kaolinite-bound organic matter did not differ significantly from that of smectite-bound organic matter. Multiple linear regression indicates that the effective cation-exchange capacity (ECEC) is the main factor to explain variance in the MRT of the extracted SOM. These results agree with previously found trends in organic matter turnover of kaolinite and smectite-associated clay.

A method for in vivo carbon-edited detection with proton echo-planar spectroscopic imaging (ICED PEPSI) is described. This method is composed of an echo-planar based acquisition implemented with C-13-H-1 J editing spectroscopy and is intended for high temporal and spatial resolution in vivo spectroscopic imaging of C-13 turnover, from D-[1,6-C-13]glucose to glutamate and glutamine, in the brain. At a static magnetic field strength of 7 T, both in vitro and in vivo chemical shift imaging data are presented with a spatial resolution of 8 mu L (i.e., 1.25 x 1.25 x 5.00 mm(3)) and a maximum spectral bandwidth of 5.2 ppm in H-1. Chemical shift imaging data acquired every 11 minutes allowed detection of regional [4-(CH2)-C-13]glutamate turnover in rat brain. The [4-(CH2)-C-13]glutamate turnover curves, which can be converted to tricarboxylic acid cycle fluxes, showed that the tricarboxylic acid cycle flux (V-TCA) in pure gray and white matter can range from 1.2 +/- 0.2 to 0.5 +/- 0.1 mu mol/g/min, respectively, for morphine-anesthetized rats. The mean cortical V-TCA from 32 voxels of 1.0 +/- 0.3 mu mol/g/min (N = 3) is in excellent agreement with previous localized measurements that have demonstrated that V-TCA can range from 0.9-1.1 mu mol/g/min under identical anesthetized conditions. (C) 1999 Wiley-Liss, Inc.