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Hiroki Taniguchi

Publications and source records attributed to Hiroki Taniguchi.

13 recordsLinked to original sources
PubMed2006

Palladium-catalyzed asymmetric silaboration of allenes.

An enantioselective silaboration of allenes was achieved using an achiral silylborane in the presence of a palladium catalyst bearing a chiral monodentate phosphine ligand. (R)-2-Bis(3,5-dimethylphenyl)phosphino-1,1'-binaphthyl gave the highest enantioselectivities in the addition of (diphenylmethylsilyl)pinacolborane to the internal C=C bond of terminal allenes at 0 degrees C, giving the corresponding beta-borylallylsilanes in high yields with high enantiomeric excesses. The enantioselectivity depended on the bulkiness of substituents of allenes: the enantiomeric excesses were found to be 91-93% ee (R = tert- and sec-alkyl), 88-90% ee (R = aryl), and 80-82% ee (R = prim-alkyl and Me) at 0 degrees C. Perfect chirality transfer was observed in the intramolecular cyclization reactions of the functionalized allylsilanes, affording highly enantioenriched cyclic alkenylboranes, which underwent Suzuki-Miyaura coupling with aryl halides.

Journal Article↗
PubMed2006

New radiofrequency coil integrated with a stereotactic frame for intraoperative MRI-controlled stereotactically guided brain surgery.

Mislocalization errors caused by MR image distortions or brain shift are one of the main causes of complications after stereotactically guided neurosurgical procedures. A special device, which could ameliorate such effects and provide intraoperative acquisition of MR images of sufficient diagnostic accuracy, was developed. It is composed of a radiofrequency receiver coil integrated with a modified Komai stereotactic frame and a Sugita four-pin head holder. Clinical testing revealed that the use of the device during stereotactically guided procedures under the control of low magnetic field strength (0.3 T) intraoperative MRI ameliorates the effects of brain shift, and permits to obtain informative tissue samples and to perform aggressive removal of the lesion without any damage of the eloquent cerebral structures. The possibility of an easy shift from a stereotactically guided to a routine microneurosurgical procedure represents an additional benefit of the developed device.

Adolescent↗
PubMed2006

Classic cadherins regulate tangential migration of precerebellar neurons in the caudal hindbrain.

Classic cadherins are calcium dependent homophilic cell adhesion molecules that play a key role in developmental processes such as morphogenesis, compartmentalization and maintenance of a tissue. They also play important roles in development and function of the nervous system. Although classic cadherins have been shown to be involved in the migration of non-neuronal cells, little is known about their role in neuronal migration. Here, we show that classic cadherins are essential for the migration of precerebellar neurons. In situ hybridization analysis shows that at least four classic cadherins, cadherin 6 (Cad6), cadherin 8 (Cad8), cadherin11 (Cad11) and N-cadherin (Ncad), are expressed in the migratory streams of lateral reticular nucleus and external cuneate nucleus (LRN/ECN) neurons. Functional analysis performed by electroporation of cadherin constructs into the hindbrain indicates requirement for cadherins in the migration of LRN/ECN neurons both in vitro and in vivo. While overexpression of full-length classic cadherins, NCAD and CAD11, has no effect on LRN/ECN neuron migration, overexpression of two dominant negative (DN) constructs, membrane-bound form and cytoplasmic form, slows it down. Introduction of a DN construct does not alter some characteristics of LRN/ECN cells as indicated by a molecular marker, TAG1, and their responsiveness to chemotropic activity of the floor plate (FP). These results suggest that classic cadherins contribute to contact-dependent mechanisms of precerebellar neuron migration probably via their adhesive property.

Animals↗
PubMed2006

Direct visualization of nucleogenesis by precerebellar neurons: involvement of ventricle-directed, radial fibre-associated migration.

Nuclei are aggregates of neurons distributed in the central nervous system and are fundamental functional units that share anatomical and physiological features. Despite their importance, the cellular basis that leads to nucleogenesis is only poorly understood. Using exo utero electroporation with an enhanced yellow fluorescent protein (EYFP) gene, we show that the precerebellar neurons derived from the lower rhombic lip (lRL) undergo multiple migration steps to form nuclei. After the unilateral transfer of EYFP to the lRL of embryonic day 12.5 mice, EYFP-labelled neurons migrate tangentially from the lRL in two distinct streams, one towards the ventral metencephalon and the other towards the ventral myelencephalon. These neurons cross the ventral midline and then become radially directed. Labelled neurons in the tangential migratory streams form contralateral clusters in the external cuneate nucleus (ECN) and lateral reticular nucleus (LRN) in the myelencephalon, and bilateral clusters in the pontine grey nucleus (PGN) and reticulotegmental nucleus (RTN) in the metencephalon. Before forming the clusters, EYFP-labelled neurons begin to migrate radially towards the ventricle in close apposition to nestin-positive radial fibres, and then they aggregate as they detach from the fibres. Inhibition of cadherin function in ECN and LRN progenitors caused ipsilateral formation of the ECN and LRN, implying that the transition of their migration from tangential to radial involves a cell-intrinsic mechanism. These observations suggest that nucleogenesis of precerebellar neurons is a result of multi-phasic migration, and that ventricle-directed radial glia-guided migration is a key step for nucleogenesis.

Animals↗
PubMed2005

Intelligent operating theater using intraoperative open-MRI.

Malignant brain tumors vary among patients and are characterized by their irregular shapes and infiltration. Localization of functional areas in the brain also differs among patients, and excess removal of tumor near eloquent areas may increase the risk of damage of function, such as motor paresis and speech disturbance. Recent progress in magnetic resonance (MR) imaging technology has enabled acquisition of intraoperative images and totally changed the neurosurgery of malignant brain tumors. Before, surgeons could merely speculate about the results of surgical manipulation and have no certainty about procedure outcomes until postoperative examination. Because intraoperative MR images allow visualization of the size of residual tumor(s) and the positional relationship between the tumor(s) and eloquent areas, surgeons are now able to achieve safe and reliable surgery. As an example, positional error on preoperative MR images caused by shifting of the brain (brain shift), a long-standing annoyance for surgeons, has been resolved using intraoperative MR images for surgical navigation, allowing precise resection. Two types of open-MR imaging scanner, a 0.2- or 0.3-tesla hamburger-type scanner with a horizontal gap and a 0.12- or 0.5-tesla double doughnut-type scanner with a vertical gap, are now available in the operating theater, and 1.5-tesla bore-type scanners are available. A 3.0-tesla bore-type scanner is planned. Intraoperative MR imaging includes diffusion-tensor and diffusion-weighted imaging, which allows visualization of nerve fibers in the white matter, especially the pyramidal tract. Such images are valuable aids in the precise resection of residual lesions of malignant brain tumors near eloquent areas without injuring motor function.

Brain Neoplasms↗
PubMed2004

Relationships between oxygen and glucose metabolism in human liver tumours: positron emission tomography using (15)O and (18)F-deoxyglucose.

BACKGROUND: Recently, investigators have measured glucose utilization in liver tumours using F-deoxyglucose positron emission tomography (FDG PET) in order to characterize tumours and predict therapeutic effects. However, the detectability of liver tumours by this method remains unclear. In addition, no study has examined the association between oxygen and glucose metabolism in liver tumours using PET. AIM: To evaluate these associations in human liver tumours in vivo using O and FDG. METHODS: Thirteen patients with liver tumours were studied: six with hepatocellular carcinoma (HCC), one with cholangiocarcinoma (CCC) and six with metastatic colon cancer (MET). We measured regional tumour blood flow (Ft), regional oxygen extraction fraction (OEF) and regional metabolic rate of oxygen (MRO2) using O PET. Using FDG PET, we determined a standardized uptake value (SUV) for liver tumours as an index of glucose metabolism. RESULTS: The mean values (mean+/-SE) for Ft, OEF, MRO2 and SUV were 42.5+/-7.0 ml x (100 g) x min, 43.4+/-4.9%, 2.57+/-0.39 ml x (100g) x min and 4.01+/-0.36, respectively. SUV for MET (4.44+/-0.48) was higher than that for HCC (3.52+/-0.59), and the blood flow in MET [31.4+/-4.1 ml x (100 g) x min] was lower than that in HCC [57.1+/-12.4 ml x (100 g) x min]. Significant negative correlations were noted between MRO2 and SUV (r=-0.741, P=0.004), and between Ft and SUV (r=-0.713, P=0.006). No correlation was apparent between Ft and OEF (r=-0.348, P=0.24), or between OEF and SUV (r=-0.023, P=0.94). CONCLUSION: O and FDG PET showed a significant negative correlation between MRO2 and SUV in human liver tumours. In addition, MRO2 depends on Ft rather than on OEF.

Adult↗
PubMed2003

Oxygen-15 positron-emission tomography for predicting selective delivery of a chemotherapeutic agent to hepatic cancers during angiotensin II-induced hypertension.

PURPOSE: Selective drug delivery is important for successful chemotherapy. In patients with hepatic cancer, we used (15)O-carbon dioxide (steady-state) and (15)O-water (dynamic) positron emission tomography (PET) to evaluate changes in blood flow induced by angiotensin (AT) II in the liver parenchyma, hepatic tumors, and spleen. METHODS: The study group comprised 13 patients, 6 with hepatic metastasis and 7 with hepatocellular carcinoma. PET was performed before and during AT II administration to induce hypertension. RESULTS: Steady-state PET images showed a preferential increase in blood flow to hepatic tumor compared with liver parenchyma during hypertension. In dynamic PET, tumor blood flow was maintained during induced hypertension while hepatic arterial blood flow, portal blood flow, total hepatic blood flow, and splenic blood flow decreased to 71.4% (not significant), 65% (P<0.01), 67.2% (P<0.001), and 72.3% (P<0.01) of the respective baseline values. CONCLUSION: AT II-induced hypertension produced a relative increase in tumor blood flow. Oxygen-15 PET should be useful for predicting preferential drug delivery to hepatic cancers.

Adult↗
PubMed2003

Differential diagnosis of gallbladder cancer using positron emission tomography with fluorine-18-labeled fluoro-deoxyglucose (FDG-PET).

BACKGROUND AND OBJECTIVES: The purpose of this paper is to evaluate the utility of positron emission tomography (PET) with fluorine-18-labeled fluoro-deoxyglucose (FDG) in the preoperative differential diagnosis of gallbladder tumors. We performed PET studies of gallbladder tumors in order to predict the malignancy of these tumors preoperatively. METHODS: Sixteen patients who had protuberant lesions in the gallbladder and who were scheduled to undergo surgery were studied with PET using FDG. Focally increased FDG uptake in the gallbladder region was considered malignant. The FDG-PET findings were compared with the histological findings of surgical pathology. RESULTS: Sensitivity of FDG-PET was 75% (6/8 patients). One of two false-negative cases suffered from diabetes mellitus, and in the other case, the lesion was small. Specificity was 87.5% (7/8 patients). A case with xanthogranulomatous cholecystitis (XGC) was the only false-positive case. CONCLUSIONS: FDG-PET may be able to provide important information for evaluating the malignancy of gallbladder tumors.

Adenocarcinoma↗
PubMed2002

Crossing the ventral midline causes neurons to change their response to floor plate and alar plate attractive cues during transmedian migration.

Neuronal migration is required for the establishment of specific neural structures, such as layers and nuclei. Neurons migrate along specific migratory routes toward their final destinations, sometimes across long distances. However, the cellular and molecular interactions that control neuronal migration are largely unknown. Here, we examined the mechanism underlying the transmedian migration of precerebellar neurons using a flat whole-mount preparation of the rat embryo. These neurons were initially attracted by the floor plate (FP) at the ventral midline. However, after crossing the midline, they lost their responsiveness to the FP and became attracted by the alar plate (AP). Although the loss of responsiveness to FP cues was caused by an encounter of migrating cells with the FP, the gain of responsiveness to AP cues occurred irrespective of their encounter with the FP. These results identify a crucial change in the response of migrating cells to attractive guidance cues during the transmedian migration of precerebellar neurons.

Animals↗
PubMed2002

Quantitative measurement of regional blood flow in hepatic focal nodular hyperplasia. Findings on positron emission tomography.

The blood flow through normal liver parenchyma and a pathologically proven hepatic region of focal nodular hyperplasia (FNH) of the lateral lobe, was measured in a single patient in a quantitative manner using regional dynamic positron emission tomography (PET) imaging with O-15 carbon dioxide (steady state) and O-15 water (dynamic state). The steady state PET images revealed higher radioactivity concentration in the lateral lobe than in the surrounding normal liver parenchyma. Regional and total blood flow in the region of FNH, as determined by the dynamic state method, was 292.2 ml/100g/min and 330.2 ml/min, respectively. It was determined that the region of FNH in this patient had higher blood flow than that described previously for liver tumors such as hepatocellularcarcinoma and colorectal hepatic metastases.

Journal Article↗
PubMedDate not supplied

Changes in hepatic parenchymal blood flow with colorectal metastases: increase in arterial and decrease in portal blood flow.

BACKGROUND/AIMS: We investigated the changes in arterial and portal blood flow in the non-tumorous liver parenchyma in the presence of colorectal hepatic metastases using the H(2)15O dynamic positron emission tomography method. METHODOLOGY: Thirty-eight patients were classified into colorectal hepatic metastases (MET), hemangioma (HEM), and no liver tumor (NR) groups. We quantitatively measured arterial blood flow and portal blood flow in each anatomical segment of the non-tumorous liver parenchyma. RESULTS: In the MET, HEM and NR groups, the non-tumorous arterial blood flow was 39.89, 32.77 and 28.85 mL/100 g/minute. Each non-tumorous portal blood flow was 71.61, 100.39 and 94 mL/100 g/minute. We observed a significant difference in arterial blood flow between MET and NR (p = 0.0296), although there was no significant difference in total blood flow among three groups. In MET, we discovered a significant correlation between tumor and non-tumorous arterial blood flow in the liver parenchyma (r = 0.7120, p = 0.0209). Non-tumorous arterial blood flow and PBF were 39.07 and 62.74 mL/100 g/minute in the segment with metastases, and 41.95 and 66.23 mL/100 g/minute without metastases. There were no significant differences in any blood flow between those with and without metastasis. CONCLUSIONS: The presence of hepatic metastases increased arterial blood flow with a compensatory decrease in portal blood flow within the non-tumorous liver parenchyma, irrespective of the number, location and size of the metastatic lesions.

Adult↗