Biomedical subjects

Masayuki Yokota

Publications and source records attributed to Masayuki Yokota.

17 recordsLinked to original sources

PubMed2006

Surface shape measurement by phase-shifting digital holography with a wavelength shift.

Surface contouring by phase-shifting digital holography is proposed and verified by experiments and numerical simulations. Digital holograms are recorded before and after mode hopping of a laser diode subject to current tuning, and the difference of the reconstructed phases at each wavelength is computed to deliver surface contours of a diffusely reflecting surface. Since normal incidence on the object is employed, the method does not need the removal of the tilt component and is free from the shadowing effect as advantages over the dual-incidence method proposed before by the first author.

Journal Article↗

PubMed2006

Image reconstruction only by phase data in phase-shifting digital holography.

We describe data compression in phase-shifting digital holography. We demonstrate by experimentation that an image of a diffusely reflecting object can be reconstructed only by phase data of the derived complex amplitude. It is shown that reduction of the bit depth of the phase data does not seriously damage the image even down to 1 bit. We observe enhancement of halo in the image with low bit depths. This tendency is verified quantitatively by a one-dimensional simulation. Our procedure for smoothing the images that result from the data-compression methods is shown to be effective.

Journal Article↗

PubMed2006

Relationship of hypotension and cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage.

OBJECTIVES: Changes in systemic arterial blood pressure and the degree of cerebral vasospasm were investigated in 125 patients with aneurysmal subarachnoid hemorrhage. METHODS: Systemic arterial blood pressure was measured every 2 hours in each patient for a period of more than 2 weeks, and a fall in systemic blood pressure (FBP) was defined as a decrease of >40 mmHg of systolic blood pressure between two consecutive measurements. RESULTS: A total of 91 FBPs occurred in 52 (41.6%) of 125 patients despite specific post-operative management to prevent hypovolemia. Five (5.5%) of the 91 FBPs occurred just before the onset of symptomatic vasospasm. Symptomatic vasospasm was observed in 36 (69.2%) of 52 patients with FBP and in 32 (43.8%) of 73 patients without FBP (p<0.01, chi-squared test). A hypodense area on computed tomographic scans in association with cerebral vasospasm was observed in 25 (48.1%) of 52 patients with FBP and in 21 (28.8%) of 73 patients without FBP (p<0.05). DISCUSSION: We conclude that FBP might result from delayed cerebral vasospasm and/or brain dysfunction owing to subarachnoid hemorrhage itself.

Aged↗

PubMed2006

Regioselective alkylation of 2-alkyl-5,6,7,8-tetrahydro-3h-cycloheptimidazol-4-ones and 2-alkyl-3h-cycloheptimidazol-4-ones.

Regioselective alkylation of 2-alkyl-5,6,7,8-tetrahydro-3H-cycloheptimidazol-4-one (1) and 2-alkyl-3H-cycloheptimidazol-4-one (2) was investigated. 3-[2'-(1-tert-Butyl-1H-tetrazol-5-yl)biphenyl-4-ylmethyl]-2-propyl-5,6,7,8-tetrahydro-1H-cycloheptimidazol-4-one (6) was preferentially obtained under the conditions by using NaH in DMF or THF. On the other hand, 3-[2'-(1-tert-butyl-1H-tetrazol-5-yl)biphenyl-4-ylmethyl]-2-propyl-5,6,7,8-tetrahydro-3H-cycloheptimidazol-4-one (5), the synthetic intermediate compound of Pratosartan, was obtained selectively in the presence of n-Bu(4)NBr in toluene by using aqueous sodium hydroxide as a base. In this reaction, it was found that the concentration of the alkaline solution influences its regioselectivity. This selectivity was observed even for aldehyde and ester derivatives.

Alkylation↗

PubMed2005

Spatial resolution of calpain-catalyzed proteolysis in focal cerebral ischemia.

Transient forebrain ischemia induces calpain-mediated degradation of the neuronal cytoskeleton, alpha-fodrin, and this results in ischemic neuronal death. In this study, we investigated the spatial distribution and temporal changes of calpain-catalyzed alpha-fodrin proteolysis in focal cerebral ischemia and examined the effects of a calpain inhibitor. Ischemia was induced in gerbils by 3-h middle cerebral artery occlusion followed by reperfusion. Animals were divided into four groups: a sham-operated group, an ischemic group, a vehicle-treated group, and a calpain inhibitor-treated group. Intravenous injections of vehicle or calpain inhibitor I were administered 30 min before ischemia. Infarct volumes were measured 1 day after reperfusion and the spatial distribution of calpain-catalyzed alpha-fodrin proteolysis was investigated by immunohistochemistry 15 min, 1 h, 4 h, and 1 day after reperfusion. Infarct volume (mean +/- SD) in the ischemic group and the vehicle-treated group was 204.6 +/- 19.1 mm3 and 212.4 +/- 16.3 mm3, respectively, and the calpain inhibitor I reduced the infarct volume [149.4 +/- 25.2 mm3 (P < 0.05)]. Immunoblot analysis demonstrated that calpain inhibitor reduced proteolysis. Ischemia induced fodrin proteolysis in the ischemic core and the peri-infarct zone within 15 min after reperfusion, with proteolysis developing quickly in the ischemic core and more slowly in the peri-infarct zone. Proteolysis preceded neuronal death in the peri-infarct zone. Calpain inhibitor I ameliorated neuronal death in the peri-infarct zone but not in the ischemic core. Thus, calpain plays a pivotal role on focal ischemia as well as in global ischemia.

Animals↗

PubMed2004

A non-enzymatic derived arachidonyl peroxide, 8-iso-prostaglandin F2 alpha, in cerebrospinal fluid of patients with aneurysmal subarachnoid hemorrhage participates in the pathogenesis of delayed cerebral vasospasm.

We performed serial measurements of 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a non-enzymatic derived arachidonyl peroxide, in the cerebrospinal fluid (CSF) of 34 patients with subarachnoid hemorrhage (SAH). Patients were treated with open or endovascular surgery within 48 h of onset. Delayed cerebral vasospasm was verified by the presence of a low-density area on CT scan indicating focal cerebral infarction occurring after symptomatic delayed vasospasm. Concentrations of 8-iso-PGF2alpha in the CSF of 15 patients exhibiting delayed cerebral vasospasm were compared with those of 19 patients who did not exhibit vasospasm. The concentrations of 8-iso-PGF2alpha in the CSF of patients showing vasospasm were 42.4+/-37.1 pg/ml (mean+/-S.D., n=12) on Days 0-2, 66.4+/-41.0 pg/ml (n=14) on Days 3-5, 118.5+/-89.9 pg/ml (n=15) on Days 6-8, 86.2+/-70.2 pg/ml (n=11) on Days 9-11, 48.8+/-31.8 pg/ml (n=10) on Days 12-14, 27.8+/-20.1 pg/ml (n=7) after Day 20, while the concentrations in patients not showing vasospasm were 24.8+/-12.0 pg/ml (n=18) on Days 0-2, 25.7+/-15.2 pg/ml (n=19) on Days 3-5, 47.5+/-52.3 pg/ml (n=18) on Days 6-8, 56.7+/-72.0 pg/ml (n=13) on Days 9-11, 34.2+/-53.1 pg/ml (n=15) on Days 12-14, 20.1+/-18.2 pg/ml (n=10) after Day 20. CSF concentrations of 8-iso-PGF2alpha on Days 3-5 and Days 6-8 were significantly higher in patients showing vasospasm as compared to patients not showing vasospasm. CSF levels of 8-iso-PGF2alpha in patients showing vasospasm gradually increased in the days after onset of SAH and peaked on Days 6-8. Levels returned to normal after Day 20. These values on Days 3-5, Days 6-8, and Days 9-11 were significantly higher than the value after Day 20. Considering these data and the biological activities of 8-iso-PGF2alpha, such as development of inflammation, membrane perturbation and vasoconstriction, we conclude that 8-iso-PGF2alpha may play a role in delayed cerebral vasospasm after SAH.

Adult↗

PubMed2004

Incorporation of arachidonic and linoleic acid hydroperoxides into cultured human umbilical vein endothelial cells.

The current study assessed the differential incorporation of 12-hydroperoxyeicosatetraenoic acid (12-HPETE), arachidonic acid (AA), 12-hydroxyeicosatetraenoic acid (12-HETE) and the linoleic acid (LA) oxidation products, 13-hydroxyoctadecadienoic acid (13-HODE) and 13-hydroperoxyoctadecadienoic acid (13-HPODE), into human umbilical vein endothelial cells (HUVEC). Approximately 80-90% of AA (10(-8)-10(-5)M) and 80% of LA (10(-8)-10(-5)M) were incorporated into HUVEC within 12h, while less than 50% of the hydroxy metabolites (12-HETE, 12-HPETE, 13-HODE, 13-HPODE) were incorporated into HUVEC over 48h. Further, treatment of HUVEC with either 12-HPETE or 13-HPODE (concentrations of 10(-5)M) had no effect on cell number at a 48h time point when compared with control. These results demonstrate that exogeneous hydroxy metabolites are incorporated into HUVEC to a lesser degree than were endogenous fatty acids. Further, we speculate that 12-HPETE and 13-HPODE are rapidly metabolized to substances without significant cytotoxic effects.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

PubMed2004

Attenuation of vascularity by preoperative radiosurgery facilitates total removal of a hypervascular hemangioblastoma at the cerebello-pontine angle: case report.

BACKGROUND: The surgical removal of solid, large, and deep-seated hemangioblastomas remains challenging because it is difficult to control bleeding during the procedure. We used preoperative radiosurgery in a solid, highly vascular hemangioblastoma at the left cerebello-pontine angle and present our angiographic, operative, and histologic findings. CASE DESCRIPTION: A 37-year-old paraplegic woman with multiple hemangioblastomas was re-admitted to our clinic with cerebellar ataxia 6 years after resection of a tumor at the fourth ventricle. A vertebral artery angiogram revealed that the 3.5 cm diameter hemangioblastoma at the left cerebello-pontine angle was highly vascular and fed by the left anterior inferior cerebellar artery and posterior inferior cerebellar artery. Nine months before surgical removal it was treated with stereotactic radiosurgery (gamma knife, margin dose 28 Gy) to inhibit tumor progression and to reduce its vascularity. The tumor was totally removed via the left lateral suboccipital approach; bleeding was well controlled and there were no complications. Pathologic examination of the content of the excised tumor revealed coagulation necrosis with hyaline degeneration of the tumor vessels, resulting in a marked decrease in its vascularity. CONCLUSION: Preoperative radiosurgery led to a marked reduction in the vascularity of this hypervascular hemangioblastoma and was useful for controlling bleeding from the tumor during resection. We succeeded to remove the vascular-rich hemangioblastma after the intentional preoperative radiosurgery. The pathologic changes induced by radiotherapy were confirmed by operative finding.

Adult↗

PubMed2004

Transoral penetration of a half-split chopstick between the basion and the dens.

A 6-year-old girl was admitted for transoral penetrating injury by a half-split chopstick. Subsequent CT imaging examinations showed that the chopstick had passed between the basion and the dens and reached the subarachnoid space just at the medulla oblongata. A sagittal reconstructed CT scan was useful for the evaluation of the injury. Imaging findings and their clinical relevance are discussed.

Brain Injuries↗

PubMed2003

Calpain induces proteolysis of neuronal cytoskeleton in ischemic gerbil forebrain.

We investigated the relationship between the activity of calcium-dependent protease (calpain) and the ischemic neuronal damage. We also investigated the mechanism of ischemic resistance in astrocytes. In gerbil, a 10-min forebrain ischemia was induced by occlusion of both common carotid arteries. The calpain-induced proteolysis of cytoskeleton (fodrin) was examined by immunohistochemistry. Immunolocalization of micro and m-calpain was also examined. Intact fodrin was observed both in neurons and astrocytes, but proteolyzed fodrin was not observed in normal brain. Fifteen minutes after ischemia, proteolysis of fodrin took place in putamen, parietal cortex and hippocampal CA1. The proteolysis extended to thalamus 4 h after ischemia after which the immunoreactivity faded down in all areas except hippocampus. On day 7, the proteolysis was still observed only in hippocampus. Neurons with the proteolysis of soma resulted in neuronal death. Throughout the experiment, the proteolysis was not observed in astrocytes. micro -Calpain was observed only in neurons but m-calpain was observed both in neurons and astrocytes. The ischemia induced only micro -calpain activation, which resulted in fodrin proteolysis of neurons with differential spatial distribution and temporal course. The proteolysis was developed rapidly and was completed within 24 h in all vulnerable regions except hippocampal CA1. The proteolysis preceded the neuronal death. The mechanism of the proteolysis seemed to be involved by Ca(2+) influx via glutamate receptor and rapid neuronal death seemed reasonable. The reason why neuronal death in CA1 evolved slowly was not clarified. In astrocytes, fodrin was not proteolyzed by m-calpain. The low Ca(2+)-sensitivity of m-calpain may be the reason of ischemic resistance in astrocytes.

Animals↗

PubMed2003

Faraday-effect optical current sensor with a garnet film/ring core in a transverse configuration.

A new scheme of the Faraday effectcurrent sensor of a magnetic ring-core type is reported. With this scheme a uniaxial magnetic garnet film is obliquely inserted into a very narrow gap in the ring core and a probe light beam is passed through the garnet film in the transverse direction to the core. It is experimentally demonstrated that this current sensor shows good sensitivity as well as good isolation from surrounding currents, particularly because of the very narrow core gap allowed. This transverse scheme is much simpler and less expensive than the known longitudinal scheme and can offer a practical optical current sensor of a ring-core type.

Journal Article↗

PubMed2003

Stabilization improvements of laser-diode closed-loop heterodyne phase-shifting interferometer for surface profile measurement.

To stabilize the phase-shifting Fizeau-type interferometer against environmental disturbances (namely, vibration and temperature variations), the feedback scheme that uses the current-induced frequency modulation of a laser diode (lambda = 633 nm) and the two-frequency optical heterodyne method has been investigated, with particular attention to improvement of the achievable stabilization. It is demonstrated that introduction of the proportional-integral control into the feedback system improves stabilization against the proportional control case; e.g., stabilization is improved 5 times for 100-nm(p-p) vibration at the frequency range at 30 Hz. The surface profile measurement for a sample mirror was conducted with a reproducibility of 6.8 nm in the root mean square under the subwavelength-amplitude vibration at 100 Hz.

Journal Article↗

PubMed2003

[A case of ruptured aneurysm of the middle cerebral artery associated with dural arteriovenous fistula in the anterior cranial fossa].

A 66-year-old man suffered from subarachnoid hemorrhage due to the rupture of a right middle cerebral artery aneurysm that was detected by 3D-CTA. He underwent an emergent clipping operation. Incidentally, postoperative DSA demonstrated dural arteriovenous fistula in the left anterior cranial fossa, which was fed by the left anterior ethmoidal artery and drained into the superior sagittal sinus via the cortical vein of the left frontal lobe. We performed electrocoagulation and division of the fistula at the second surgery. Subsequently, he underwent a ventriculo-peritoneal shunt and was discharged without any neurological deficits. We reviewed reported cases of rare association of ruptured cerebral aneurysm and dural arteriovenous fistula in the left anterior cranial fossa.

Aged↗

PubMed2002

Fiber-linked Faraday effect current sensor by use of a flint glass cell with dielectric-coated retardation-compensated total reflection surfaces.

A new type of Faraday effect optical current transformer has been developed that uses a single block of square flint glass with dielectric-coated total reflection surfaces as the sensing element. Numerical calculation has shown that the coating of two dielectric layers of 45.59-nm-thick Ta2O5 and 448.35-nm-thick SiO2 films on a flint glass surface produces zero retardation total reflection for the 45 degrees incident angle of light at lambda = 840 nm with great incident angle, wavelength, and film thickness tolerances. A fiber-linked current transformer has been constructed and experimentally demonstrated to exhibit high isolation from surrounding currents as well as high stability against mechanical disturbances.

Journal Article↗

PubMed2002

Carbapenem antibiotics inhibit valproic acid transport in Caco-2 cell monolayers.

The concomitant use of carbapenem antibiotics with valproic acid has been prohibited because carbapenems induced a decrease in plasma concentration of valproic acid in epileptic patients during valproic acid therapy. Our previous in vivo study in rats proposed that inhibition by carbapenem of the intestinal absorption of valproic acid might be a possible mechanism for the drug-drug interaction. To demonstrate the hypothesis, we examined the effects of imipenem and panipenem on intestinal transepithelial transport of valproic acid using Caco-2 cell monolayers. Imipenem and panipenem inhibited the transport of [14C]-valproic acid across the Caco-2 cell monolayers from apical-to-basolateral side in a concentration-dependent manner, although they had no effect on the uptake of [14C]-valproic acid by Caco-2 cells. The inhibition by the carbapenems of the valproic acid transport was found even when they were added to only the basolateral side. From these results, the carbapenems may inhibit the absorption of valproic acid at the basolateral membrane of intestinal epithelial cells, which contributes to the decrease in plasma concentration of valproic acid after oral administration.

Anticonvulsants↗

PubMed2002

Brain-specific angiogenesis inhibitor 1 (BAI1) is expressed in human cerebral neuronal cells.

Brain-specific angiogenesis inhibitor 1 (BAI1) is a p53-target gene specifically expressed in the brain. We examined the distribution of the endogenous BAI1 protein in normal human brain tissue using a polyclonal antibody against the extracellular region of BAI1. Immunohistochemical study demonstrated that BAI1 was expressed in neuronal cells of the cerebral cortex but not in astrocytes. BAI1 protein was localized in the cellular cytoplasm and membrane. It was predominantly localized in the cellular membrane when expressed in cultured cells by means of gene transfection. BAI1 protein may play an important role in neuronal functions such as synapse formation and signal transduction.

Adult↗

PubMed2002

Polymer-stabilized liquid crystal blue phases.

Blue phases are types of liquid crystal phases that appear in a temperature range between a chiral nematic phase and an isotropic liquid phase. Because blue phases have a three-dimensional cubic structure with lattice periods of several hundred nanometres, they exhibit selective Bragg reflections in the range of visible light corresponding to the cubic lattice. From the viewpoint of applications, although blue phases are of interest for fast light modulators or tunable photonic crystals, the very narrow temperature range, usually less than a few kelvin, within which blue phases exist has always been a problem. Here we show the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260-326 K). Furthermore, we demonstrate an electro-optical switching with a response time of the order of 10(-4) s for the stabilized blue phases at room temperature.

Journal Article↗