Slicing Conditions Research Articles

Post-Newtonian Equations of Motion in the Flat Universe

Using the (3 + 1) formalism, we derive the post-Newtonian (PN) equations of motion in a flat unvierse. To derive the equations of motion, we must carefully consider two points, one being the choice of the density in the Newtonian order (ρN) and the other the choice of the gauge condition. In choosing ρN, we require that the density fluctuation ρN - ρ0 agrees with a gauge invariant quantity in the linear approximation theory. As a gauge condition, we propose the cosmological post-Newtonian (CPN) slice condition with the pseudo transverse-traceless gauge condition, by which the evolution of the geometric variables derived in the PN approximation in the early stage of universe agrees with that of the gauge invariant quantities in the linear approximation. In the derived equations of motion, the force is calculated from six potentials which satisfy the Poisson equations. Hence, our formalism can be easily applied to numerical simulations in which the standard technique (e.g., particle-mesh method) is used. We apply the PN formula to the one-dimensional (1D) Zel'dovich solution to demonstrate that our strategy works well, and also to determine the effect of the PN forces on the evolution of the large-scale structure. It is found that the behavior of the density fluctuation and metric quantities in the early stage obtained by the present formalism agrees with that of the gauge invariant quantities in the linear approximation, although they do not always agree within the previous formalism due to the appearance of spurious gauge modes. We also discuss the evolution of the non-linear density fluctuation with very large scale, which may be affected by the PN correction in the last stage of the evolution.

Acute dopamine depletion potentiates independent stimulatory and inhibitory D 1 DA receptor-mediated control of striatal acetylcholine release in vitro

Fractional release of [ 3H]ACh was evaluated under basal and evoked conditions in striatal slices from normal and acutely dopamine-depleted adult rats for the influence of D 1- and D 2-DA receptor agonists. The D 1 ligand had no effect on normal slices but DA depletion unmasked two independent but simultaneous supersensitive responses: augmentation of K +-evoked and inhibition of glutamate-evoked release. The D 2 ligand inhibited evoked release in normal slices and this effect was not potentiated. This is a new cholinergic model of acute D 1 receptor supersensitivity.

Numerical black holes: A moving grid approach.

Spherically symmetric (1D) black-hole spacetimes are considered as a test for numerical relativity. A finite difference code, based in the hyperbolic structure of Einstein's equations with the harmonic slicing condition is presented. Significant errors in the mass function are shown to arise from the steep gradient zone behind the black hole horizon, which challenge the Computational Fluid Dynamics numerical methods used in the code. The formalism is extended to moving numerical grids, which are adapted to follow horizon motion. The black hole exterior region can then be modeled with higher accuracy.

N-acetylbenzidine and N,N'-diacetylbenzidine formation by rat and human liver slices exposed to benzidine.

The extent to which N-acetylbenzidine and N,N'-diacetylbenzidine are formed may influence benzidine-induced carcinogenesis. This study compared the formation of these metabolites by rat and human liver slices. The relationship between the NAT2 genotype and the formation of these acetylated products was also evaluated in humans. In rat liver slices incubated with 0.05 mM [3H]benzidine for 1 h (n = 3), N-acetylbenzidine and N,N'-diacetylbenzidine represented 8.8 +/- 3.6 and 73 +/- 2.5% respectively of the total radioactivity recovered by HPLC. No unmetabolized benzidine was observed. This suggests that an equilibrium exists between benzidine, N-acetylbenzidine and N,N'-diacetylbenzidine in rat liver slice incubations which favors N,N'-diacetylbenzidine formation. In the presence of 0.1 mM paraoxon, a deacetylase inhibitor, N-acetylbenzidine and N,N'-diacetylbenzidine increased to 13 +/- 0.6 and 79 +/- 0.3% respectively. Within 2 h after incubating human liver slices with 0.014 mM [3H]benzidine (n = 8), benzidine, N-acetylbenzidine and N,N'-diacetylbenzidine represented 19 +/- 5, 34 +/- 4 and 1.6 +/- 0.5%, respectively, of the total radioactivity recovered by HPLC. Thus in the human, conditions in liver slices favor N-acetylbenzidine rather than N,N'-diacetylbenzidine formation. With paraoxon, benzidine, N-acetylbenzidine and N,N'-diacetylbenzidine represented 2 +/- 0.4, 24 +/- 4 and 51 +/- 3%, respectively. This resulted in a 32-fold increase in N,N'-diacetylbenzidine formation. Individuals with rapid NAT2 genotypes formed 1.4-fold more N-acetylbenzidine than slow acetylators. However, this increase was not significant. There was no apparent correlation of N,N'-diacetylbenzidine formation with NAT2 genotype. Similar results were observed when human slices were incubated with 0.09 mM [3H]benzidine. Deacetylase, perhaps more than N-acetyltransferase, influences hepatic metabolism and subsequent carcinogenesis of benzidine in man. These results help explain the species and organ specificity of benzidine carcinogenesis.

Differential responses between CA1 pyramidal cells and dentate gyrus granule cells to ischemia-like conditions in rat hippocampal slices

Differential responses between CA1 pyramidal cells and dentate gyrus granule cells to ischemia-like conditions in rat hippocampal slices

Effect of potassium channel modulators on the release of glutamate induced by ischaemic-like conditions in rat hippocampal slices

The effects of the potassium channel openers lemakalim, RP 52891 and galanin and the potassium channel blockers glibenclamide and gliquidone were evaluated by the release of endogenous glutamate from rat hippocampal slices subjected to a brief period of ischaemia (2–10 min). Ischaemia was mimicked by incubating slices in a glucose free medium equilibrated with 95% N 2 5% CO 2 . These conditions evoked a release of glutamate which was insensitive to tetrodotoxin and Ca 2+ indicating a non-vesicular origin. The release of glutamate evoked by a 6- or 8-min period of ischaemia was reduced by 25–40% in the presence of lemakalim (10 μM), RP 52891 (10 μM) or galanin (0.3 μM), whereas it was enhanced by 60 to 100% in the presence of glibenclamide (1 μM) and gliquidone (2 μM). These observations suggest that cellular damage resulting from ischaemia induced excessive release of glutamate in the hippocampus may be partly reduced by potassium channel openers, and conversely increased by sulfonylureas.

A finite element method in space and time for relativistic spherical collapse

The finite element method is applied in space and time to spherically symmetric collapse in general relativity. The fluid equations are discretized with a weighted residual method in which isoparametric, bilinear approximations on quadrilaterals are used. The metric equations are constraint equations, and are approximated with cubic and linear functions on triangles. The time slices and nodal movement can be chosen arbitrarily, and a number of choices are investigated. These include a maximal slicing condition which requires an additional solution of a differential equation. The code is tested with the Riemann shock tube, and then compared with a mixed finite element/finite difference code and with a smoothed particle hydrodynamics code. Three particular simulations are used for comparisons: static, freefall collapse and collapse-and-bounce. The finite element method agrees well with the other codes, and will produce accurate results with extremely “bent” time slices.

The effects of the adenosine reuptake inhibitor soluflazine on synaptic potentials and population hypoxic depolarizations in area CA1 of rat hippocampus in vitro

Adenosine has recently been shown to play a potentially important role in the regulation of synaptic excitability during experimental hypoxia in the hippocampus of the rat. Endogenous adenosine, rapidly released at the initiation of a hypoxic episode, produced synaptic depression, which could protect sensitive neurons. In the present experiments, an inhibitor of the reuptake of adenosine, soluflazine (R64719) was employed to increase the levels of endogenous adenosine under normoxic and hypoxic conditions in slices of the hippocampus of the rat. Soluflazine produced a slow-onset, concentration-dependent depression of population excitatory postsynaptic potentials, which was reversed by the specific A 1 adenosine receptor antagonist, 8-cyclopentyltheophylline. During severe N 2-induced hypoxia, soluflazine significantly delayed hypoxic depolarization. These results suggest that inhibition of the reuptake of adenosine may have therapeutic potential in the amelioration of hypoxic/ischemic neuronal damage, particularly in the hippocampus.

Calcium elevations induced by in vitro ischemia-like conditions in gerbil hippocampal and cerebellar slices

Calcium elevations induced by in vitro ischemia-like conditions in gerbil hippocampal and cerebellar slices

Identification and Characterization of Cysteinyl‐Leukotriene Formation in Tissue Slices from Human Intracranial Tumors: Evidence for Their Biosynthesis Under In Vivo Conditions

In previous studies, it had been shown that human gray and white matter tissue slices have the capacity to synthesize large amounts of cysteinyl-leukotrienes (cysteinyl-LT) in vitro. This study was initiated to investigate cysteinyl-LT formation by tissue slices from intracranial tumors in comparison with cyclooxygenase products such as prostaglandin (PG) F2 alpha and thromboxane (TX) B2. Tissue slices from meningiomas and astrocytomas were found to release large amounts of cysteinyl-LT spontaneously and even higher amounts after ionophore A 23187 stimulation, which could not be accounted for by blood possibly remaining in the tissue slices. Cysteinyl-LT were identified by their immunoreactive characteristics, their biological activity in the guinea pig ileum bioassay, and their retention time on reversed-phase HPLC. With increasing malignancy, astrocytomas were shown to have an increasing biosynthetic capacity for cysteinyl-LT and TXB2 in vitro. In comparison with meningioma patients, malignant astrocytoma patients had an enhanced urinary excretion of LTE4, the major urinary metabolite of cysteinyl-LT in humans, which dropped in level within 7 days after operation by 79%. A correlation exists between the in vivo cysteinyl-LT production in patients with malignant astrocytomas and that observed under basal conditions in the tissue slices in vitro. The results provide evidence that in malignant astrocytoma patients, the tumor tissue produces large amounts of cysteinyl-LT, which may be detected in the patients' urine.

N-methylaspartate receptors mediate epileptiform activity evoked in some, but not all, conditions in rat neocortical slices

Using intracellular recordings from pyramidal neurons in isolated slices of rat cerebral cortex epileptiform discharges evoked (1) in the presence of γ-aminobutyric acid antagonists, and (2) in the absence of Mg 2+ were compared. Depolarization shift responses recorded in the presence of bath applied picrotoxin, or electrophoretically applied picrotoxin or bicuculline, were similar in many respects to depolarization shifts reported previously, except that they could be evoked by stimuli subthreshold for evoking discernible postsynaptic potentials in these experiments. Large depolarizations evoked by repetitive activation of an N-methylaspartate receptor mediated synapse in the absence of Mg 2+, displayed several properties similar to those of depolarization shifts evoked in the presence of γ-aminobutyric acid antagonists, i.e. similar shape, latency, inability to follow high repetition rates and a similar voltage relation, suggesting activation of the same cellular mechanism. “Slow spikes” evoked as part of the response to electrophoretically applied N-methylaspartate were augmented, i.e. they were replaced by larger, longer, more complex events, when γ-aminobutyric acid antagonists were applied. The potentiated response, evoked in the absence of Mg 2+, was dependent on the activation of an N-methylaspartate receptor mediated synapse and was blocked by N-methylaspartate antagonists. In contrast, depolarization shifts could be evoked in the presence of large doses of N-methylaspartate antagonists, when γ-aminobutyric acid antagonists were applied. Spontaneous depolarizations similar to depolarization shifts were recorded when cells were exposed to low, tonic, electrophoretic applications of excitatory amino acids under control conditions. In addition, some potentiation of the N-methylaspartate receptor mediated excitatory postsynaptic potential was achieved in the presence of Mg 2+ when cells were depolarized by 10–20mV. Depolarization shifts evoked when bicuculline was applied electrophoretically to different parts of the dendritic field, some hundreds of microns from the soma, differed in shape, latency and time course and the depolarization shift evoked when bicuculline was applied at one site summed with the depolarization shift evoked when it was applied elsewhere. We conclude that different inputs are required to activate the responses evoked in the presence of γ-aminobutyric acid antagonists and in the absence of Mg 2+. The possibility that both involve activation of dendritic Ca 2+currents and that the magnitude of the response depends on the proportion of the dendritic field activated, is discussed.

Voltage-dependent currents in neurones of the nuclei of the solitary tract of rat brainstem slices

Neurones within the ventral and ventrolateral nuclei of the solitary tract were analyzed under single-electrode current- and voltage-clamp conditions in rat brainstem slices. We present direct and indirect evidence for the existence of five different sorts of membrane currents: a tetrodotoxin-sensitive sodium current, a tetrodotoxin-resistant calcium current, a calcium-dependent potassium current, a non-inactivating potassium current which is inhibited by muscarine, an inactivating potassium current, which is inhibited by 4-aminopyridine. These membrane properties do not produce spontaneous bursting in these neurones. Assuming that neurones with such properties belong to the respiratory network, we discuss how conductances of this type may be involved in mechanisms regulating central respiratory activity.

Effects of phencyclidine on the release and synthesis of newly formed dopamine

The effect of phencyclidine (PCP) on the release and synthesis of [ 3H]-dopamine ([ 3H]-DA) newly synthesized from [3,5- 3H]- l-tyrosine was studied under both basal and potassium-stimulated conditions in slices from the rat striatum. Phencyclidine (3–100 μM) stimulated the release of [ 3H]-DA during superfusion with low level potassium (4.5 mM) buffer, but had no effect on the release of [ 3H]-DA elicited by superfusion with buffer containing 40 mM potassium. On the other hand, phenycyclidine had no effect (except at 100 μm) on the spontaneous release of [ 3H]-H 2O (formed as a result of the hydroxylation of [3,5- 3H]- l-tyrosine), but inhibited the increase in formation of [ 3H]-H 2O normally associated with potassium-induced depolarization. These data are discussed in relation to results obtained with phencyclidine on other in vitro and in vivo models of dopaminergic function.

Action of the venom of the scorpion Tityus trinitatis on pancreatic insulin secretion

In vivo, canine pancreas was stimulated to secrete insulin by the venom of the scorpion Tityus trinitatis; the venom also caused a rise in plasma glucose level as well. The venom-induced insulin secretion was also observed under in vitro conditions in rat pancreative slices, and this stimulation was dose-related. Maximal effect was observed at 20 μg/ml. Atropine (3 × 10 −6 M) completely abolished both venom (20 μg/ml)- and acetylcholine (3 × 10 −7 M)-induced insulin secretion. It is suggested that the venom-induced insulin secretion is mediated through muscarinic cholinergic mechanisms.

An Analytic Solution of Initial Data for Slowly Rotating Dust Sphere under Maximal Slicing Condition

An Analytic Solution of Initial Data for Slowly Rotating Dust Sphere under Maximal Slicing Condition

Gravitational Collapse of Charged Dust Shell and Maximal Slicing Condition

The maximal slicing condition is a good time coordinate condition qualitatively when pursuing the gravitational collapse by the numerical calculation. The analytic solution of the gravitational collapse under the maximal slicing condition is given in the case of a spherical charged dust shell and the behavior of time slices with this coordinate condition is investigated. It is concluded that under the maximal slicing condition we can pursue the gravitational collapse until the radius of the shell decreases to about 0.7X (the radius of the event horizon).

Effects of HCO 3−/CO 2 on the cytochrome redox potential and metabolic responses of isolated rat cerebral cortex

The importance of HCO 3 −/CO 2 to the maintenance of stable metabolic conditions in rat cerebral cortex slices has been investigated. Replacement of bicarbonate buffered media with glycylglycine or phosphate buffered salines resulted in an increased lability of the cytochrome redox potential of brain slices as measured by dual wavelength spectroscopy. Depletion of reduced cytochrome in the electron transport chain was associated with changes in the metabolic responses of tissues to electrical stimulation or elevated concentrations of potassium. This appears primarily as a loss of the late reductive responses of the tissue nicotinamide adenine dinucleotides NAD(P)H to these stimuli and decreased lactic acid output of the tissues. The effects could be largely reversed in a combined glycylglycine and HCO 3 −/CO 2 buffered media. It is suggested that although the reduction of NAD(P) in response to stimulation may be substantially located in the cytosol, it is also modulated by the mitochondrial redox potential. It is suggested that the lability of the redox potential in the absence of HCO 3 −/CO 2 may be related to depletion of TCA cycle intermediates normally replaced by CO 2 fixation.

The existence of maximal slicings in asymptotically flat spacetimes

We consider Cauchy data (g, π) on IR3 that are asymptotically Euclidean and that satisfy the vacuum constraint equations of general relativity. Only those (g, π) are treated that can be joined by a curve of “sufficiently bounded” initial data to the trivial data (δ, 0). It is shown that in the Cauchy developments of such data, the maximal slicing condition tr π=0 can always be satisfied. The proof uses the recently introduced “weighted Sobolev spaces” of Nirenberg, Walker, and Cantor.

The effect of lithium on acetylcholine release and synthesis

When sodium concentration in Krebs solution was replaced by different concentrations of lithium to maintain isosmolarity, the acetylcholine release during resting conditions in rat cortex slices was increased depending on the lithium concentration. The maximal augmentation in ACh resting release was reached at a lithium concentration of 117.9 mM. This acetylcholine release proved to be tetrodotoxin (2.5 × 10 −7 g ml ) and noradrenaline (10 −6 g ml ) resistant. However, when sodium was partly replaced by lithium (117.9 mM LiCl and 25 mM NaCl) the synthesis was blocked completely. This inhibition can be attributed to the lithium ions present in the nerve terminals, since the acetylcholine release was unaffected at low sodium concentration (25 mM) when isosmolarity was maintained by glucose. Furthermore lithium (117.9 mM) reduced the acetylcholine output due to stimulation from the nerve terminals of guinea-pig ileum longitudinal muscle strip. It is suggested that lithium accumulating inside the nerve terminals inhibited the rate of synthesis of acetylcholine. The reduction of freshly synthetized acetylcholine led to a reduction of acetylcholine output due to stimulation.

Dihydrotestosterone in prostatic hypertrophy. I. The formation and content of dihydrotestosterone in the hypertrophic prostate of man.

To explore the relation between androgens and prostatic hypertrophy in man, the concentrations of testosterone, dihydrotestosterone, and androstenedione and the rate of conversion of testosterone to dihydrotestosterone have been measured in normal and hypertrophic prostate tissue. First, a double isotope derivative technique was adapted for the measurement of tissue androgen content in 15 normal and 10 hypertrophic prostates. Although there was no significant difference in the content of androstenedione and testosterone between the two types of tissue, the content of dihydrotestosterone was significantly greater in the hypertrophic tissue (0.60 +/-0.10 mug/100 g) than in the normal glands (0.13 +/-0.05 mug/100 g). Second, a regional study was performed in three normal prostates and four glands with early hypertrophy, and it was demonstrated that the dihydrotestosterone content was two and three fold greater in the periurethral area where prostatic hypertrophy usually commences than in the outer regions of the gland. Finally, the rate of conversion of testosterone to dihydrotestosterone has been measured under standardized conditions in tissue slices from 4 normal and 20 hypertrophic prostates. There was no significant difference in the rate of dihydrotestosterone formation between the two types of gland (6.0 +/-0.8 and 7.8 +/-0.5 mumumoles/15 mg of tissue per hr). While the mechanism by which dihydrotestosterone accumulation occurs remains unexplained, it is possible that the local accumulation of dihydrotestosterone may be involved in the pathogenesis of prostatic hypertrophy in man.