Determination of neutron energy spectrum at KAMINI shielding experiment location.

The neutron spectrum at KAMINI reactor south beam tube end has been determined using multifoil activation method. This beam tube is being used for characterizing neutron attenuation of novel shield materials. Starting from a computed guess spectrum, the spectrum adjustment/unfolding procedure makes use of minimization of a modified constraint function representing (a) least squared deviations between the measured and calculated reaction rates, (b) a measure of sharp fluctuations in the adjusted spectrum and (c) the square of the deviation of adjusted spectrum from the guess spectrum. The adjusted/unfolded spectrum predicts the reaction rates accurately. The results of this new procedure are compared with those of widely used SAND-II code.

Measurement and prediction of neutron spectra in the Kalpakkam mini reactor (KAMINI).

Kalpakkam mini (KAMINI) reactor is the newest research reactor built in India. Operated at the Indira Gandhi Centre for Atomic Research, Kalpakkam, it has the unique distinction of being the only operating pool-type reactor in the world at present fuelled by 233U and aluminium alloy. Neutron spectra have been measured by the multi-foil irradiation method at the beam tube ends of this reactor. The spectra unfolding have been done, by using SAND-II computer code. Thus the total and thermal flux at the beam tube ends have been measured. The theoretical spectrum generated by the computer codes SMAXY and COMESH and WIMS cross-section data library was compared with the measured spectrum for one of the beam tubes and found to match well. A new 620-group cross-section data library generated at our centre was tested with SAND-II for the same set of measurements. Use of the new library results in slightly higher measured total fluxes and smoother spectra shapes.

Regional metabolic alterations in Alzheimer's disease: an in vitro 1H NMR study of the hippocampus and cerebellum.

The concentrations of selected metabolites in the hippocampus and cerebellum of 13 Alzheimer's diseased (AD) and four nondemented postmortem brains were measured using high resolution 1H NMR spectroscopy. For both the hippocampal region and the cerebellum, the putative neuronal marker N-acetyl aspartate (NAA) was significantly lower in AD brains relative to the nondemented brains. For the hippocampal region, the NAA concentration correlated inversely with semiquantitative assessments of neuronal loss and neurofibrillary tangles. The gamma-aminobutyric acid levels in both hippocampus and cerebellum of an age- and a postmortem interval-matched subset of AD brains were lower than those of the controls. Because the cerebellum is generally thought to be unaffected by AD, the NAA decrease in the Alzheimer cerebellum may be due to lesions of either the Alzheimer or non-Alzheimer type in contralateral cerebrum.

An in vitro 1H nuclear magnetic resonance study of the temporoparietal cortex of Alzheimer brains.

The concentrations of selected metabolites in the posterior temporoparietal cortex of 13 Alzheimer's diseased (AD) and four nondemented postmortem brains (of individuals between the ages of 63 and 95) were determined using high-resolution 1H nuclear magnetic resonance (NMR) spectroscopy. The estimates for glutamate and inositol for AD brains did not show any statistically significant difference (P > 0.05) from those for the nondemented brains. The putative neuronal marker N-acetyl aspartate (NAA), creatine, and GABA were decreased in AD brains compared with the nondemented brains. The estimates for creatine, glutamate, and GABA showed significant linear correlations with those of NAA. Creatine, glutamate, GABA, and NAA appeared to be negatively correlated with the neurofibrillary tangles. Our results support a neuronal loss in the posterior temporoparietal cortices of AD brains.

In vivo 7Li nuclear magnetic resonance study of lithium pharmacokinetics and chemical shift imaging in psychiatric patients.

New data are presented on the application of 7Li in vivo nuclear magnetic resonance (NMR) spectroscopy to human studies. The technique was used to monitor the between-dose pharmacokinetics of lithium (Li) in brain for three patients on Li therapy. Brain Li concentrations were at their highest from 0 to 2 hours after the peak occurred in serum concentration. Elimination from brain tissue took longer than elimination from muscle, and no signal could be detected from brain at 10 days after termination of therapy. A birdcage radiofrequency coil for 7Li was constructed and used to measure the 7Li spin-lattice relaxation time of 4.6 seconds in vivo in human head, and to acquire preliminary spectroscopic images of a phantom and human brain.

Fluoxetine and trifluoperazine in human brain: a 19F-nuclear magnetic resonance spectroscopy study.

Fluorine-19 (19F) is a nonradioactive isotope that is well-suited to nuclear magnetic resonance spectroscopy (NMRS) and is a constituent of several medications used to treat psychiatric illnesses. Fluoxetine, a trifluorinated agent, generated a signal from brain that was readily measured by 19F-NMRS. Estimated brain concentrations ranged from 1.3-5.7 micrograms/ml in six subjects at a steady state dose of 40 mg/day. Enhanced sensitivity of 19F has been obtained by conforming the surface coil to the shape of the forehead. Hence, at the current state of development, 19F-NMRS can be applied to clinical questions relevant to concentrations of fluoxetine in brain. We also report observation of NMRS signals from fluorinated neuroleptics in a number of patients at steady state. These signals continue to be difficult to obtain, although a correlation between dose and estimated brain concentrations is suggested.

Regulation of the oxidative phosphorylation rate in the intact cell.

The mechanisms that underlie the balance between the consumption and oxidative generation of ATP in the intact cell are not well-defined. Cytosolic inorganic phosphate (Pi) and ADP levels, the cytosolic ATP/ADP ratio, and the cytosolic phosphorylation potential (PP) have all been proposed as major regulatory variables, the latter as a component of a "near-equilibrium" thermodynamic regulatory scheme. Therefore, the potential regulatory roles of these variables in the intact cell were evaluated with 31P NMR and Langendorff perfused rat hearts; in this preparation, the tissue oxygen consumption rate (MVO2) can be varied over a wide range. When the exogenous carbon source was varied, none of the proposed regulatory parameters, i.e., the ATP/ADP ratio, PP, or cytosolic ADP level, were found to be uniquely related to MVO2. Rather, ADP levels at a given MVO2 decreased progressively for the exogenous carbon sources in the following order: glucose, glucose + insulin, palmitate + glucose, lactate, pyruvate + glucose, and octanoate + glucose. In the octanoate and pyruvate groups, MVO2(-1) was linearly dependent upon [ADP]-1 with apparent Km values being in the range previously observed in isolated mitochondria. A similar trend was observed in the MVO2-[Pi] relationship. The present findings suggest that exogenous carbon sources which effectuate deregulation of intramitochondrial NADH generation lower cytosolic ADP and Pi to levels which are limiting to the rate of oxidative phosphorylation. For other carbon sources, the processes controlling the rate of NADH generation also participate in determining the rate of oxidative ATP synthesis. However, this control must be exerted kinetically rather than through a near-equilibrium thermodynamic mechanism as indicated by the present data and prior kinetic studies of the ATP synthetic process in both isolated mitochondria and intact myocardium [La Noue, K. F., et al. (1986) Biochemistry 25, 7667-7675; Kingsley-Hickman, P., et al. (1987) Biochemistry 26, 7501-7510].

Alterations in oxidative function and respiratory regulation in the post-ischemic myocardium.

In the normal and post-ischemic, isovolumic Langendorff perfused rat hearts, 31P NMR spectra and mechanical performance were evaluated over a wide range of myocardial oxygen consumption rates (MVO2). Hearts were perfused with either glucose and insulin, palmitate and glucose, or pyruvate and glucose as exogenous carbon sources. After ischemia at 38 degrees C until the onset of ischemic contracture and subsequent reperfusion, the "free" ADP levels were significantly reduced as compared to controls. In the control palmitate + glucose and glucose + insulin groups, the ADP levels were virtually independent of approximately 2.5-fold variation in MVO2; in contrast, they changed 4-fold with a approximately 30% variation in MVO2 in the post-ischemic myocardium following ischemia to contracture. In the pyruvate + glucose group, ADP levels varied with MVO2 in controls and post-ischemia; however, MVO2-ADP relationship was significantly altered following ischemia. Analysis of these observations within the concept of kinetic regulation of oxidative phosphorylation yielded the following significant conclusions: 1) the mode of respiratory regulation changed from a non-ADP to an "ADP:Pi limited" domain with non-pyruvate carbon sources; 2) respiratory regulation was in the ADP:Pi limited domain before and after ischemia in the pyruvate + glucose group; however, the Km for the relationship between MVO2 and ADP was reduced following the ischemia/reperfusion insult; 3) the post-ischemic oxidative capacity (Vmax for MVO2) was significantly reduced in all groups and this reduction would limit maximal post-ischemic mechanical performance.

31P NMR studies of ATP synthesis and hydrolysis kinetics in the intact myocardium.

The origin of the nuclear magnetic resonance (NMR)-measurable ATP in equilibrium Pi exchange and whether it can be used to determine net oxidative ATP synthesis rates in the intact myocardium were examined by detailed measurements of ATP in equilibrium Pi exchange rates in both directions as a function of the myocardial oxygen consumption rate (MVO2) in (1) glucose-perfused, isovolumic rat hearts with normal glycolytic activity and (2) pyruvate-perfused hearts where glycolytic activity was reduced or eliminated either by depletion of their endogenous glycogen or by use of the inhibitor iodoacetate. In glucose-perfused hearts, the Pi----ATP rate measured by the conventional two-site saturation transfer (CST) technique remained constant while MVO2 was increased approximately 2-fold. When the glycolytic activity was reduced, the Pi----ATP rate decreased significantly, demonstrating the existence of a significant glycolytic contribution. Upon elimination of the glycolytic component, the measured Pi----ATP rates displayed a linear dependence on MVO (micromoles of O consumption rate) with a slope of 2.36 +/- 0.15 (N = 8, standard error of the mean). This linear relationship is expected if the rate determined by CST is the net rate of ATP synthesis by the oxidative phosphorylation process, in which case the slope must equal the P:O ratio. The ATP----Pi rates and rate:MVO ratios measured by the multiple-site saturation transfer method at two MVO2 levels were equal to the corresponding Pi----ATP rates and rate:MVO ratios obtained in the absence of a glycolytic contribution. The following conclusions are drawn from these studies: (1) unless the glycolytic contribution to the ATP in equilibrium Pi exchange is inhibited or is specifically shown not to exist, the myocardial Pi in equilibrium ATP exchange due to oxidative phosphorylation cannot be studied by NMR; (2) at moderate MVO2 levels, the reaction catalyzed by the two glycolytic enzymes glyceraldehyde-3-phosphate dehydrogenase and 3-phosphoglycerate kinase is near equilibrium; (3) the ATP synthesis by the mitochondrial H+-ATPase occurs unidirectionally (i.e., the reaction is far out of equilibrium); (4) the "operative" P:O ratio in the intact myocardium under our conditions is significantly less than the canonically accepted value of 3.

Difference circular dichroism studies of copper and nickel binding to D-penicillamine in the presence of human serum albumin.

The binding of copper and nickel to D-penicillamine in the presence of human serum albumin (HSA) has been studied using difference circular dichroism (CD). The difference CD spectra due to penicillamine in HSA-Cu2+-penicillamine systems at pH 6 are indicative of ternary complexes between HSA, copper and penicillamine. On the other hand, the difference spectra due to penicillamine in HSA-Ni2+-penicillamine systems resemble that due to the Ni2+-penicillamine complex, indicating that mostly binary complexes are formed. The formation of stable complexes between penicillamine and copper or nickel (whether they are of the binary or mixed ligand type) may be important in the therapeutic action of this drug.

Chloride ion nuclear magnetic resonance spectroscopy probe studies of copper and nickel binding to serum albumins.

The binding of Cu2+ and Ni2+ to bovine, dog, and human serum albumin has been studied by the 35Cl NMR probe technique. The number of primary copper sites were estimated to be 1.3 for human serum albumin, 3.1 for bovine serum albumin, and 6.6 for dog serum albumin. A similar number of primary nickel sites was determined for each of these albumins. On the basis of the chloride probe experiments, it appears that both copper and nickel have the same binding sites on albumin.

Copper and nickel binding to canine serum albumin. A circular dichroism study.

The binding of copper and nickel to canine serum albumin has been studied using circular dichroism. In the 320-700 nm region, only a single positive extremum was observed at about 664-667.5 nm for copper bound to canine serum albumin. The intensity of this extremum was found to increase until a Cu2+/albumin molar ratio of 3 was reached. Further addition of Cu2+ led to a decrease in ellipticity. The absence of any extrema in the 560-570 and 480-510 nm regions showed that histidines were not involved in copper binding to canine albumin. In the case of nickel, initial binding was found to take place at the N-terminal tripeptide. At higher nickel to albumin molar ratios, circular dichroism spectra indicated the presence sulfur containing ligands but showed no evidence for the involvement of histidines. Canine serum albumin was found to bind six or more Cu2+ and Ni2+ ions with affinities that are lower than for human or bovine serum albumin.

A proton nuclear magnetic resonance study of the interaction of cadmium with human erythrocytes.

The binding of Cd2+ by molecules in the intracellular region of human erythrocytes has been studied by 1H-NMR spectroscopy. From changes in spin-echo Fourier transform NMR spectra for both intact and hemolyzed erythrocytes to which CdCl2 was added, direct evidence was obtained for the binding of Cd2+ by intracellular glutathione and hemoglobin. Time-courses were measured by 1H-NMR for the uptake of Cd2+ by intact erythrocytes in saline/glucose solution and in whole blood. In both cases, the uptake, as indicated by changes in the 1H-NMR spectrum for intracellular glutathione, plateaus after about 30 min. The effectiveness of the disodium salt of EDTA and of various thiol-chelating agents for releasing glutathione from its Cd2 + complexes in hemolyzed erythrocytes was also studied. EDTA was found to be more effective than thiols, and dithiols more effective than monothiols.

Ion-specific electrode study of copper binding to serum albumins.

The binding of copper to bovine, human, rabbit, rat, and porcine albumin has been studied using a cupric ion-specific electrode. The results were analyzed in terms of Scatchard expression assuming two classes of independent binding sites. The high-affinity constants for copper binding to the albumin show the same trend as the first association constants for nickel binding, namely, rabbit greater than human greater than rat greater than pig. Despite the similarity in the primary amino acid sequence for human and bovine serum albumin, the former has only one high-affinity site for copper, while the latter has more than three sites.