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T Ohta

Publications and source records attributed to T Ohta.

At least 37 records · Page 2Linked to original sources
PubMed2004

Chaos in an exact relativistic three-body self-gravitating system.

We consider the problem of three-body motion for a relativistic one-dimensional self-gravitating system. After describing the canonical decomposition of the action, we find an exact expression for the three-body Hamiltonian, implicitly determined in terms of the four coordinates and momentum degrees of freedom in the system. Nonrelativistically these degrees of freedom can be rewritten in terms of a single particle moving in a two-dimensional hexagonal well. We find the exact relativistic generalization of this potential, along with its post-Newtonian approximation. We then specialize to the equal-mass case and numerically solve the equations of motion that follow from the Hamiltonian. Working in hexagonal-well coordinates, we obtain orbits in both the hexagonal and three-body representations of the system, and plot the Poincaré sections as a function of the relativistic energy parameter eta. We find two broad categories of periodic and quasiperiodic motions that we refer to as the annulus and pretzel patterns, as well as a set of chaotic motions that appear in the region of phase space between these two types. Despite the high degree of nonlinearity in the relativistic system, we find that the global structure of its phase space remains qualitatively the same as its nonrelativistic counterpart for all values of eta that we could study. However, the relativistic system has a weaker symmetry and so its Poincare section develops an asymmetric distortion that increases with increasing eta. For the post-Newtonian system we find that it experiences a chaotic transition in the interval 0.21<theta<0.26, above which some of the near-integrable regions degenerate into chaos.

Journal Article↗
PubMed2004

Fluvoxamine, a selective serotonin reuptake inhibitor, suppresses tetrahydrobiopterin in the mouse hippocampus.

In the present study, we investigated the effects of fluvoxamine, a selective serotonin reuptake inhibitor, on brain tetrahydrobiopterin (BH4) levels. We directly measured levels of BH4 by Tani and Ohno's direct method as well as the serotonin (5-HT) turnover ratio, i.e. 5-hydroxyindoleacetic acid (5-HIAA)/5-HT, after sub-acute s.c. injection of fluvoxamine in the hippocampus of mice. Our animal model incorporated two risk factors of depression, social isolation and acute environmental change. Male ddY mice (6W) were housed in isolation (1 per cage; 35 days), injected with fluvoxamine (20 or 40 mg/kg; days 29-35), and exposed to novelty stress (20 min; day 35). In the stress session, behavioral parameters, i.e. total distance and rearing behavior, were measured. Isolation housing increased both behaviors. Fluvoxamine attenuated rearing behavior, but did not influence total distance. Isolation housing increased BH4 levels. Novelty stress increased BH4 levels in group housing, although it did not change them in isolation housing. Fluvoxamine suppressed BH4 levels. In isolation housing, fluvoxamine increased 5-HT turnover ratios, while it decreased them in group housing. In conclusion, fluvoxamine, housing condition, and novelty stress regulated BH4 levels. Fluvoxamine may have changed behavior and 5-HT turnover by suppressing BH4 levels as well as by inhibiting 5-HT reuptake.

Animals↗
PubMed2004

Gluteal compartment syndrome after abdominal aortic aneurysm repair.

A 66-year-old man underwent emergency surgery for a ruptured abdominal aortic aneurysm associated with right common and internal iliac aneurysms. Postoperatively, his right buttock was distended and tender to compression. A CT scan revealed an extremely swollen right gluteus maximus with decreased density. Macromyoglobinuria was noted, and creatine kinase and myoglobin were elevated: 87,800 IU/l and 144,300 ng/ml, respectively. Renal function had deteriorated and he was treated with hemodialysis until the 15th postoperative day. The patient recovered without any discomfort to the buttock or intermittent claudication. To our knowledge this is the first documented case of gluteal compartment syndrome after the repair of an abdominal aortic aneurysm.

Aged↗
PubMed2004

Acute myelogenous leukemia in a donor after granulocyte colony-stimulating factor-primed peripheral blood stem cell harvest.

This article describes the first case of acute myeloid leukemia (AML) in a healthy donor at 14 months after granulocyte colony-stimulating factor (G-CSF)-primed peripheral blood stem cell (PBSC) harvest. In September 2001, a healthy 61-year-old female was given G-CSF prior to PBSC harvest for her brother with multiple myeloma. In spite of successful engraftment, the recipient died from a disease relapse. In November 2002, the donor, admitted with high fever and leukocytosis with 98.5% blastoid cells, was diagnosed as having AML (M1). Her leukemia cells were positive for CD13, CD33, and G-CSF receptor without chromosomal abnormality and responded to G-CSF in vitro. During chemotherapy, she died of progressive pneumonia. If our case is truly the first, the incidence of leukemia in donors may not be higher than that of naturally occurring leukemia. However, efforts towards an international long-term study, or at least to report every case similar to ours, would be required to be conclusive.

Female↗
PubMed2004

A newly designed disposable introducer sheath for a ventricular fiberscope.

We have developed a disposable plastic introducer sheath for use with a flexible endoscope during intraventricular procedures. The sheath is composed of a thin polypropylene tube passing through the center of a plastic stopper. The tube serves as a sheath through which the fiberscope is introduced into the ventricle. The stopper seats in the burr hole and prevents downward and lateral movement of the tube. The sheath can be placed safely in the ventricle with a drainage catheter used as an introducing guide. We used this sheath system in 10 patients and found it very useful. Manipulation of the fiberscope was not hindered, copious irrigation was allowed, and the sheath remained stable on the skull. This new introducer sheath may contribute to the increased use of a flexible endoscope in neuroendoscopic procedures.

Cerebral Ventricles↗
PubMed2004

Genome architecture studied by nanoscale imaging: analyses among bacterial phyla and their implication to eukaryotic genome folding.

The proper function of the genome largely depends on the higher order architecture of the chromosome. Our previous application of nanotechnology to the questions regarding the structural basis for such macromolecular dynamics has shown that the higher order architecture of the Escherichia coli genome (nucleoid) is achieved via several steps of DNA folding (Kim et al., 2004). In this study, the hierarchy of genome organization was compared among E. coli, Staphylococcus aureus and Clostridium perfringens. A one-molecule-imaging technique, atomic force microscopy (AFM), was applied to the E. coli cells on a cover glass that were successively treated with a detergent, and demonstrated that the nucleoids consist of a fundamental fibrous structure with a diameter of 80 nm that was further dissected into a 40-nm fiber. An application of this on-substrate procedure to the S. aureus and the C. perfringens nucleoids revealed that they also possessed the 40- and 80-nm fibers that were sustainable in the mild detergent solution. The E. coli nucleoid dynamically changed its structure during cell growth; the 80-nm fibers releasable from the cell could be transformed into a tightly packed state depending upon the expression of Dps. However, the S. aureus and the C. perfringens nucleoids never underwent such tight compaction when they reached stationary phase. Bioinformatic analysis suggested that this was possibly due to the lack of a nucleoid protein, Dps, in both species. AFM analysis revealed that both the mitotic chromosome and the interphase chromatin of human cells were also composed of 80-nm fibers. Taking all together, we propose a structural model of the bacterial nucleoid in which a fundamental mechanism of chromosome packing is common in both prokaryotes and eukaryotes.

Bacterial Proteins↗
PubMed2004

Changes in the concentrations of tetrahydrobiopterin, the cofactor of tyrosine hydroxylase, in blood under physical stress and in depression.

This paper studies changes in the concentrations of tetrahydrobiopterin (BH4), the cofactor of tyrosine hydroxylase, in blood under physical stress and in depression. BH4 was found to be transiently released from the sympathetic nerves under severe physical stress but continuously released in depression with an increased oxidation rate of BH4 to B.

Adolescent↗
PubMed2003

Identification of four highly conserved genes between breakpoint hotspots BP1 and BP2 of the Prader-Willi/Angelman syndromes deletion region that have undergone evolutionary transposition mediated by flanking duplicons.

Prader-Willi and Angelman syndromes (PWS and AS) typically result from an approximately 4-Mb deletion of human chromosome 15q11-q13, with clustered breakpoints (BP) at either of two proximal sites (BP1 and BP2) and one distal site (BP3). HERC2 and other duplicons map to these BP regions, with the 2-Mb PWS/AS imprinted domain just distal of BP2. Previously, the presence of genes and their imprinted status have not been examined between BP1 and BP2. Here, we identify two known (CYFIP1 and GCP5) and two novel (NIPA1 and NIPA2) genes in this region in human and their orthologs in mouse chromosome 7C. These genes are expressed from a broad range of tissues and are nonimprinted, as they are expressed in cells derived from normal individuals, patients with PWS or AS, and the corresponding mouse models. However, replication-timing studies in the mouse reveal that they are located in a genomic domain showing asynchronous replication, a feature typically ascribed to monoallelically expressed loci. The novel genes NIPA1 and NIPA2 each encode putative polypeptides with nine transmembrane domains, suggesting function as receptors or as transporters. Phylogenetic analyses show that NIPA1 and NIPA2 are highly conserved in vertebrate species, with ancestral members in invertebrates and plants. Intriguingly, evolutionary studies show conservation of the four-gene cassette between BP1 and BP2 in human, including NIPA1/2, CYFIP1, and GCP5, and proximity to the Herc2 gene in both mouse and Fugu. These observations support a model in which duplications of the HERC2 gene at BP3 in primates first flanked the four-gene cassette, with subsequent transposition of these four unique genes by a HERC2 duplicon-mediated process to form the BP1-BP2 region. Duplicons therefore appear to mediate genomic fluidity in both disease and evolutionary processes.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Neurons but not glial cells show reciprocal imprinting of sense and antisense transcripts of Ube3a.

The human UBE3A gene shows brain-specific partial imprinting, and lack of a maternally inherited allele causes Angelman syndrome (AS), which is characterized by neurobehavioral anomalies. In several AS model mice, imprinted Ube3a expression is detected predominantly in the hippocampus, cerebellar Purkinje cells and the olfactory bulb. Therefore, imprinting of mouse Ube3a is thought to be region-specific with different levels of silencing of the paternal Ube3a allele in different brain regions. To determine cell types of imprinted Ube3a expression, we analyzed its imprinting status in embryonic brain cells by using primary cortical cell cultures. RT-PCR and immunofluorescence were performed to determine the allelic expression of the gene. The Ube3a gene encodes two RNA transcripts in the brain, sense and antisense. The sense transcript was expressed maternally in neurons but biallelically in glial cells in the embryonic brain, whereas the antisense transcript was expressed only in neurons and only from the paternal allele. Our data present evidence of brain cell type-specific imprinting, i.e. neuron-specific imprinting of Ube3a in primary brain cell cultures. Reciprocal imprinting of sense and antisense transcripts present only in neurons suggests that the neuron-specific imprinting mechanism is related to the lineage determination of neural stem cells.

Angelman Syndrome↗
PubMed2003

Chaos in a relativistic 3-body self-gravitating system.

We consider the 3-body problem in relativistic lineal [i.e., (1+1)-dimensional] gravity and obtain an exact expression for its Hamiltonian and equations of motion. While general-relativistic effects yield more tightly bound orbits of higher frequency compared to their nonrelativistic counterparts, as energy increases we find in the equal-mass case no evidence for either global chaos or a breakdown from regular to chaotic motion, despite the high degree of nonlinearity in the system. We find numerical evidence for mild chaos and a countably infinite class of nonchaotic orbits, yielding a fractal structure in the outer regions of the Poincaré plot.

Journal Article↗
PubMed2003

The Lotus japonicus Sen1 gene controls rhizobial differentiation into nitrogen-fixing bacteroids in nodules.

A Lotus japonicus mutant, Ljsym75, which forms ineffective symbiotic nodules and defines a new locus involved in the process of nitrogen fixation, was characterized in detail in order to identify the stage of developmental arrest of the nodules. No nitrogen-fixing activity was detectable in Ljsym75 nodules at any stage during plant development, and plant growth was markedly retarded. Ljsym75 plants formed twice as many nodules as the wild-type Gifu, and this phenotype was not influenced by the application of low concentrations of nitrate. Although the ineffective nodules formed on Ljsym75 were anatomically similar to effective Gifu nodules, Ljsym75 nodules senesced prematurely. Microscopic examination revealed that bacteria endocytosed into Ljsym75 nodules failed to differentiate into bacteroids. Moreover, the bacteria contained no nitrogenase proteins, whereas leghemoglobin was detected in the cytosol of the nodules. These results indicate that Ljsym75 is required for bacterial differentiation into nitrogen-fixing bacteroids in nodules, and thus the Ljsym75 gene was renamed sen1 (for stationary endosymbiont nodule). Linkage analysis using DNA markers showed that Sen1 is located on chromosome 4.

Chromosome Mapping↗
PubMed2003

Adsorption of thiolates to singly coordinated sites on Au111 evidenced by photoelectron diffraction.

The adsorption structure of methylthiolate (CH3S) adsorbed on Au(111), a long-standing controversial issue, has been unambiguously determined by scanned-energy and scanned-angle S 2p photoelectron diffraction. The methylthiolate molecules are found to occupy atop sites with a S-Au distance of 2.42 +/- 0.03 A. The angular distribution of the S 2p photoelectrons due to forward scattering reveals that the S-C bond is inclined by approximately 50 degrees from the surface normal towards both the [211] and [121] (nearest-neighbor thiolate) directions.

Journal Article↗
PubMed2003

Effects of intravascular perfusion of cooled crystalloid solution on cold-induced brain injury using an extracorporeal cooling-filtration system.

BACKGROUND: We evaluated cerebral metabolic change during brain hypothermia with intravascular perfusion of cooled crystalloid solution using an extracorporeal cooling-filtration system and cerebroprotective effects of this hypothermia on brain injury in an animal model. METHOD: Microdialysis probes were implanted into the bilateral parietal cortices. A cold-induced brain injury was produced behind the microdialysis probe on the right parietal cortex. Immediately after injury in the cooled group (n=9), Ringer's solution cooled to 5 degrees C was infused into the right vertebral artery after occlusion of the bilateral common carotid and the left vertebral arteries. Excessive fluid was ultrafiltrated by a dialyzer. Brain temperature was maintained at about 20 degrees C for 60 minutes. In 7 dogs, three neck arteries were occluded for 60 minutes after injury without cooled fluid infusion. The extracellular concentrations of glutamate, lactate, and pyruvate were measured serially for 180 minutes after injury. FINDINGS: Extracellular glutamate concentrations in the cooled group did not increase, while there was a significant increase in the injured hemisphere as compared to the uninjured hemisphere in the non-cooled group ( P<0.05). Extracellular lactate concentrations increased slightly after occlusion in both groups. The depth of cortical injury was limited in the cooled group, but extended into the white matter in the non-cooled group up to 240 minutes after injury. INTERPRETATION: Occlusion of three main arteries induced ischaemia under critical threshold in canine brains. Under this condition, intravascular cooling with crystalloid solution suppressed accumulation of extracellular glutamate and reduced tissue damage in the early phase after cold-induced brain injury, as cerebroprotective effects. This information suggests that a method employing brain hypothermia via intra-arterial cooling with an extracorporeal cooling-filtration system has potential to achieve successful, safe, selective brain cooling.

Animals↗
PubMed2003

Conservative treatment of a second trimester cervicoisthmic pregnancy diagnosed by magnetic resonance imaging.

BACKGROUND: A cervicoisthmic pregnancy, which may be carried to term, is potentially dangerous for the pregnant woman. With ultrasonographic evaluation alone the diagnosis of a cervical pregnancy in the second trimester is difficult. CASE: A nulliparous 33-year-old woman at 21 weeks' gestation was diagnosed by ultrafast T2-weighted magnetic resonance imaging (MRI) to have a cervicoisthmic pregnancy. After the infant was delivered live by cesarean with a vertical fundal incision, methotrexate was infused into the placenta via the umbilical vein. The next day she received uterine artery methotrexate infusion and embolization with platinum coils. Eight months later there was no trace of the placenta on ultrasonography or MRI. She subsequently resumed normal menstrual cycles, conceived, and delivered a healthy infant at term by cesarean after 2 years. CONCLUSION: This report describes MRI and successful preservation of fertility with such an advanced cervicoisthmic pregnancy.

Adult↗
PubMed2003

Preventive effects of sequential treatment with alendronate and 1 alpha-hydroxyvitamin D3 on bone mass and strength in ovariectomized rats.

Because accumulating evidence has shown that bisphosphonates are unable to maintain their bone-sparing effects after the withdrawal of the drug, a replacement treatment is needed when bisphosphonate treatment cannot be continued for some reason. The present study investigated the preventive effects of alendronate followed by 1alpha(OH)D3 on the mass and mechanical strength of trabecular and cortical bones in ovariectomized rats. Sprague-Dawley rats were ovariectomized or sham-operated at 48 weeks of age. Ovariectomized rats treated with vehicle alone (OVX group) showed significant decreases in bone mineral density (BMD) and mechanical strength of the lumbar vertebra and the midfemur during a 20-week period after the operation as compared with sham-operated rats. These decreases were prevented by continuous treatment with alendronate (0.5 mg/kg/day, po) for 20 weeks (ALN-C group), whereas the values reverted to those of the OVX group when alendronate was withdrawn at 10 weeks (ALN-W group). The sequential treatment with alendronate and 1alpha(OH)D3 (0.05 microg/kg/day, po) for 10 weeks each (ALN --> 1alpha group) resulted in higher BMD and mechanical strength of the lumbar vertebra and the midfemur in this group than in the OVX and ALN-W groups. The increase in mechanical strength was proportional to that in BMD at both sites, suggesting that the stimulatory effects of these treatments on bone strength were due to those on bone mass. Analyses of histology, computed tomography, and biochemical markers confirmed the preventive effects of the sequential treatment. Therefore, we propose that 1alpha(OH)D3 may be a good choice to replace alendronate when alendronate treatment cannot be continued for some reason.

Aging↗
PubMed2003

GENIA corpus--semantically annotated corpus for bio-textmining.

MOTIVATION: Natural language processing (NLP) methods are regarded as being useful to raise the potential of text mining from biological literature. The lack of an extensively annotated corpus of this literature, however, causes a major bottleneck for applying NLP techniques. GENIA corpus is being developed to provide reference materials to let NLP techniques work for bio-textmining. RESULTS: GENIA corpus version 3.0 consisting of 2000 MEDLINE abstracts has been released with more than 400,000 words and almost 100,000 annotations for biological terms.

Abstracting and Indexing↗