A magnetic heterostructure of topological insulators as a candidate for an axion insulator.

The axion insulator which may exhibit an exotic quantized magnetoelectric effect is one of the most interesting quantum phases predicted for the three-dimensional topological insulator (TI). The axion insulator state is expected to show up in magnetically doped TIs with magnetizations pointing inwards and outwards from the respective surfaces. Towards the realization of the axion insulator, we here engineered a TI heterostructure in which magnetic ions (Cr) are modulation-doped only in the vicinity of the top and bottom surfaces of the TI ((Bi,Sb)2Te3) film. A separation layer between the two magnetic layers weakens interlayer coupling between them, enabling the magnetization reversal of individual layers. We demonstrate the realization of the axion insulator by observing a zero Hall plateau (ZHP) (where both the Hall and longitudinal conductivity become zero) in the electric transport properties, excluding the other possible origins for the ZHP. The manifestation of the axion insulator can lead to a new stage of research on novel magnetoelectric responses in topological matter.

Characteristics of a granular electronic system in Heusler-type Fe2+xV1-xAl.

We report comprehensive measurements of the magnetic, transport, and thermal properties of the Heusler-type compound Fe2+xV1-xAl, with x values near the ferromagnetic quantum critical point, xc âˆ¼ 0.05. At T âˆ¼ 60 K, a prominent Schottky-like anomaly appeared in the specific heat; this anomaly was correlated with a smaller pseudo-gap formation in magnetic susceptibility, magnetoresistance, and thermoelectric power. Furthermore, a magnetic anomaly observed in the magnetic susceptibility and resistivity at T âˆ¼ 4 K was suppressed significantly by applying a magnetic field. A magnetically inhomogeneous phase arose below T âˆ¼ 60 K, which appeared to consist of ferromagnetic and paramagnetic clusters.

Electronic structure of the band-filling-controlled CaVO3 and LaVO3 compounds.

We studied the electronic structure of the band-filling CaVO(3) and LaVO(3) compounds. The experimental techniques were photoemission (PES) and x-ray absorption (XAS) spectroscopy. The experimental results were analyzed using an extended cluster model. The ground states of CaVO(3) and LaVO(3) are highly covalent and contain a considerable 3d(n + 1)L contribution. The CaVO(3) compound is in the charge transfer regime (Δ < U), whereas the LaVO(3) material is in the intermediate regime (Δ âˆ¼ U). The spectral weight distributions reveal that CaVO(3) is a coherent metal and that LaVO(3) is a p-d insulator. The photoemission of CaVO(3) shows the coherent peak (3d(1)C) and the incoherent feature (3d(1)L). The spectrum of insulating LaVO(3) presents only the incoherent structure (3d(2)L), whereas the coherent peak is replaced by the Mott-Hubbard screening (3d(2)D). This transfer of spectral weight is responsible for the opening of the experimental bandgap. The incoherent feature contains a considerable O 2p character and cannot be attributed to the lower Hubbard band. Further, the relative V 3d-O 2p cross section helps to explain the photon energy dependence of the PES spectra. The addition spectra of both CaVO(3) and LaVO(3) are dominated by the 3d(n + 1) final state configuration. The distribution of spectral weight is mainly dictated by intra-atomic exchange and crystal field splittings. The coherent contribution is less important than in photoemission, and is greatly diminished in the O 1s x-ray absorption spectra.

Pyrogenic cytokines injected into the rat cerebral ventricle induce cyclooxygenase-2 in brain endothelial cells and also upregulate their receptors.

Peripheral immunological insults induce interleukin (IL)-1 beta and IL-6 in the brain. To elucidate the mechanism(s) of fever evoked by these brain-derived cytokines, and possible interactions between them, we examined in rats: (i) whether cyclooxygenase-2 is responsible for fever evoked by central injection of these cytokines; (ii) if so, where in the brain cyclooxygenase-2 is induced; (iii) where the receptors for these cytokines are located; and (iv) how the expression of these receptors is influenced by the cytokines. Intracerebroventricular injection of these cytokines evoked fever that was suppressed by a cyclooxygenase-2 inhibitor. Brain endothelium was the site of cyclooxygenase-2 induction by these cytokines. IL-1 receptor (IL-1R) was constitutively expressed in brain endothelium, and its mRNA was further upregulated by either cytokine. IL-6R mRNA was constitutively expressed in the cerebral cortex, and was newly induced in as yet unidentified cells in brain blood vessels by either cytokine. Messenger RNAs for cyclooxygenase-2, IL-1R, and IL-6R were often observed in the same blood vessels. These results suggest that COX-2 induced in brain endothelium is, at least in part, involved in the fever evoked by these cytokines, and that one possible interaction between these two cytokines is mutual upregulation of their receptors in the endothelium or perivascular cells, resulting in augmentation of their actions.

Protective effect of prostaglandin I(2) analogs on ischemic delayed neuronal damage in gerbils.

We found a novel subtype of prostaglandin (PG) I(2) receptor (IP(2)) expressed in the central nervous system. Recently we have demonstrated that (15R)-16-m-tolyl-17,18,19, 20-tetranorisocarbacyclin (15R-TIC) and 15-deoxy-16-m-tolyl-17,18,19, 20-tetranorisocarbacyclin (15-deoxy-TIC), IP(2)-specific ligands, significantly prevented high (50%) oxygen-induced apoptotic neuronal death in cultured hippocampal neurons. We report here a potent neuroprotective effect of such analogs on delayed neuronal death of hippocampal CA1 neurons following transient ischemia for 3 min in gerbils. (15S)-16-m-tolyl-17,18,19,20-tetranorisocarbacyclin (15S-TIC), which nonselectively acts both on the PGI(2) receptor expressed in the peripheral tissue (IP(1)) and on IP(2), also showed a neuroprotective effect on such an ischemic model at higher doses than those for 15R-TIC and 15-deoxy-TIC. These PGI(2) analogs did not affect brain temperature, indicating that the agents showed the neuroprotective effect not by a hypothermic effect, but rather by the direct action on neurons.

[Intensive and high-dose chemotherapy with peripheral blood stem cell transfusion for pediatric malignant brain tumor].

In this study, the newly developed marrow-rescue therapy during myelosuppression is utilized. In this therapy, peripheral blood stem cell transfusion (PBSCT) is administered following high-dose chemotherapy. Harvest of peripheral blood stem cells (PBSC) during myelosuppression following marrow-ablative chemotherapy is a safe, reliable procedure in children with leukemia. And administration of these cryopreserved PBSC is useful in reducing myelosuppression following intensive/ultra high-dose chemotherapy. In this study, several courses of intensive chemotherapy (1 course: VP-16 300mg/m2 x 5 days + carboplatin 400-500mg/m2 x 3 days) and one course of ultra-high dose chemotherapy (1 course: VP-16 400mg/m2 x 8 days + carboplatin 800mg/m2 x 5 days + MCNU 250, 200mg/m2 x each day) with PBSC transfusion were applied in four cases of pediatric malignant brain tumors (2 cases of medulloblastoma, one case of pineoblastoma and anaplastic ependymoma) after surgical reduction. With PBSC transfusion, myelosuppression following high-dose chemotherapy could be overcome without serious complication in all cases. Three cases showed complete remission and one showed partial remission after the operation and intensive chemotherapy. However, CSF dissemination appeared in two cases and they died 20 and 28 months after the onset respectively. Intensive/ultra high-dose chemotherapy with PBSC transfusion is a safe procedure in children with malignant brain tumors. This procedure may enable the postponement of radiation for pediatric malignant brain tumor cases under three years of age.

[Clinicopathological study on choroid plexus tumors: immunohistochemical features and argyrophilic nucleolar organizer regions values].

Immunohistochemical features and numbers of argyrophilic nucleolar organizer regions (Ag-NORs) were investigated on 6 cases with choroid plexus tumors: 3 adult and one pediatric cases with choroid plexus papilloma (CPP) and 2 pediatric cases with choroid plexus carcinoma (CPC) clinicopathologically. One of the 2 children with CPC developed a recurrence with dissemination to the CSF and died 2 years postoperatively (case 6), while the other survived following surgery (case 5). This outcome suggested the existence of biological differences in these tumors. We conducted an immunohistochemical examination of prealbumin, S-100 protein, glial fibrillary acidic protein (GFAP), cytokeratin (CKER), and epithelial membrane antigen (EMA) using avidin-biotin complex (ABC) methods and the silver colloid staining technique for Ag-NORs. All 4 CPP were positive for prealbumin and S-100 protein, with 3 of them being strongly positive; 3 of 4 were positive for GFAP and 2 were positive for CKER and EMA. Two cases of CPC were weakly positive for prealbumin. However the part of reserved papillary structure of case 5 was strongly positive for it. The tumor of the survived child was positive for S-100, GFAP, CKER, while negative for EMA. A positivity for S-100 protein and prealbumin was associated with a good outcome, whereas that for GFAP, CKER, and EMA was not. The mean number of Ag-NORs in the 2 cases with CPC exceeded that in cases with CPP. Of the 2 cases with CPC, fetal one (case 6) showed a higher number of Ag-NORs than the survived patient.(ABSTRACT TRUNCATED AT 250 WORDS)

[MRI findings and endocrinological dysfunction in hemorrhagic pituitary adenoma].

Magnetic resonance image (MRI) findings, intraoperative macroscopic findings and endocrinological functions were reported in 13 cases of hemorrhagic pituitary adenoma (HPA) according to clinical severity. The cases were divided into 3 groups: (1) classical pituitary apoplexy (PA) (n = 2), (2) subacute PA (n = 4), (3) asymptomatic HPA (n = 7). Based on MRI intensity and intraoperative findings, there were 7 cases with hemorrhagic PA and 5 with necrotic cyst formation. MRI intensities predicted the cyst contents, either hemorrhagic or xanthochromic, more accurately than CT findings. In addition, two classical cases of the PA group disclosed niveau formation on MRI, but MRI intensity in the first case differed from that in the second case. Classical PA of the first case occurred during the pregnancy. MRI intensity in the case 7 months after the onset disclosed high intensity of the upper part and normointensity of the lower part. T1 weighted image and proton image showed homogeneous intensity. On the contrast, PA of the second case showed water-like intensity on the upper part and methemoglobin-like intensity on the lower part. These different MRI intensities suggest different etiologies of niveau formation. MRI findings in the first case may indicate the chronic stage of massive intratumoral hemorrhage but the mechanism may be the same in both cases. From MRI intensity and clinical course, the cause of niveau formation in the second case is similar to that found in the literature. That is, hemorrhage was thought to have occurred in the pre-existing cyst cavity.(ABSTRACT TRUNCATED AT 250 WORDS)

[Intracranial MR imaging of achondroplasia].

Intracranial MR imaging was performed in five patients with achondroplasia. All patients had narrowing of the subarachnoid space at the level of the foramen magnum that was mainly due to protrusion of the posterior aspect. Three patients had compressive deformities of the brainstem and/or upper cervical spine. Among them, two patients had deformities of the pons. Relative upward displacement of the brainstem was seen in all patients. Hydrocephalus was seen in three patients.

The association of hypopituitarism with small pituitary, invisible pituitary stalk, type 1 Arnold-Chiari malformation, and syringomyelia in seven patients born in breech position: a further proof of birth injury theory on the pathogenesis of "idiopathic hypopituitarism".

We report seven cases of hypopituitarism all having a history of breech delivery, asphyxia at birth, and syringomyelia. A small pituitary gland was found on MRI or CT in six cases, invisible pituitary stalk on MRI in five cases, and type 1 Arnold-Chiari malformation in six cases. A constellation of these abnormalities are best explained by traction of brain and spinal cord of the subjects exerted during breech delivery and further support the primary role of birth trauma in the genesis of "idiopathic hypopituitarism".

[A case of intraventricular cyst associated with normal pressure hydrocephalic condition].

A case of intraventricular cyst associated with normal pressure hydrocephalic condition (NPHC) is reported. A 72 year-old female, with 2-year-history of slowly progressing dementia and gait disturbance, was admitted to our hospital on September 19, 1989. On admission, she had mild dementia, unsteadiness of gait, and at times urinary incontinence. Cerebrospinal fluid (CSF) pressure was found to be 90mmH2O by lumbar tap. Plain computed tomographic (CT) scan and T1-weighted magnetic resonance image (MRI) showed asymmetrical enlargement of the trigon and posterior horn of the right lateral ventricle. CT cisternography showed a cyst in the trigon and in the posterior horn of the right lateral ventricle. T1-weighted MRI with Gd-DTPA demonstrated no enhancement of the cyst wall, and there was superior and posteromedial displacement of the choroid plexus at the trigon of the right lateral ventricle. The patient was diagnosed as having an intraventricular cyst in the right trigon with NPHC. Ventriculo-peritoneal shunt and partial removal of the cyst were performed. Histological examination of the cyst wall revealed collagenous strands and no epithelial cells. Developmental intracranial cysts, especially arachnoid or ependymal cysts, occasionally lack an epithelial layer, so their histological diagnosis is difficult. This case was considered to be an arachnoid cyst because there was adhesion between the cyst and the choroid plexus in the right trigon, and superior, posteromedial displacement of the choroid plexus, which indicated extension of the cyst from the extracerebral to the intracerebral region. NPHC was considered to be due to disturbance of CSF circulation caused by gradual expansion of the cyst.

Serum levels of glycated albumin in non-diabetic and insulin-dependent diabetic children.

The serum levels of glycated albumin (GA) in 83 non-diabetic children and 26 children with insulin-dependent diabetes mellitus (IDDM) were measured by high-performance liquid chromatography (HPLC). In non-diabetic children over one year, the GA levels were found to be uninfluenced by age, while the fructosamine (FRA) levels increased with age. The mean level of GA in IDDM children was 39.1 +/- 9.1%, which was significantly higher than in non-diabetic children with values of 16.1 +/- 1.1% (p less than 0.01). The GA levels of non-diabetic and IDDM children did not overlap, whereas their FRA levels did overlap. The GA levels correlated with HbAlc levels (r = 0.74, p less than 0.01) and FRA levels (r = 0.66, p less than 0.01) in IDDM children. The GA levels were more closely correlated than the FRA levels with the blood glucose two and three weeks previously. Thus, the GA level is a useful indicator of short-term control in diabetes mellitus.

[A case of a basilar bifurcation aneurysm associated with common carotid artery occlusion].

A case of a basilar bifurcation aneurysm associated with common carotid artery occlusion is reported. A 40-year-old woman was admitted to our hospital with severe headache and nausea. On admission, no neurological abnormality was observed. CT scan showed thin subarachnoid hemorrhage in the basal cistern. Left vertebral angiograms revealed a basilar bifurcation aneurysm located in the high position. Also, the left internal and external carotid arteries were supplied through the anastomotic muscle branches of the left occipital and vertebral artery. The trunk of the left common carotid artery was not visualised from its origin on the aortogram. CT scan at the level of C6 showed thinning of the left common carotid artery and contrast enhancement study indicated occlusion. Neck clipping of the aneurysm was successfully performed by right trans-sylvian approach. Right zygomatic arch was removed to obtain a wider operative field for avoiding further retraction of the brain tissue. The postoperative course was uneventful except transient disorientation for two weeks. It has been well known that internal carotid artery occlusion may be associated with cerebral aneurysm in some cases. However, it seemed to be a rather rare case that the common carotid artery occlusion due to arteriosclerosis was associated with cerebral aneurysm. Hemodynamic factor was positively suggested for aneurysmal formation in this case.

Alterations in fructosamine and glycated albumin levels during childhood.

Age-related changes in the blood concentrations of glycated proteins during childhood and adolescence were examined by measuring the blood fructosamine (FA), glycated albumin (GA), glucose levels and total serum protein levels in 611 healthy children (325 boys and 286 girls) aged 0-18 years old. These levels were compared with those of 130 healthy adults. GA was measured by a newly developed, highly precise method of high-performance liquid chromatography (inter-assay coefficient of variation, 4.9%). The FA values of all groups of up to 15 years old (grouped in two year age brackets) were significantly lower than those of adults. The mean serum concentrations of GA in infants up to four years old were also significantly lower than in adults. A slight but statistically significant positive correlation was found between age and values of FA (r = 0.36, P less than 0.001), but not of GA (r = 0.04). Levels of total serum proteins showed a positive correlation with those of FA (r = 0.47, P less than 0.001) but a weak correlation with those of GA (r = 0.29). These results suggest that age should be taken into account when the FA levels of children and the GA values of infants are evaluated.

[The effect of aortic valve translocation and a few problems].

Aortic valve endocarditis is frequently associated with an aortic root abscess, so that it is difficult to insert a prosthetic valve. Between April, 1983 and June, 1988 we treated four out of seven patients with aortic valve endocarditis by translocation of the aortic valve, closure of the native coronary ostia, and placement of saphenous vein grafts on the coronary arteries. In each case, the operation was undertaken because of rapidly progressing heart failure. Infection was due to alpha-Streptococcus in two instances, to Staphylococcus epidermidis and fungus in the other cases. In one of the four patients, the prosthetic aortic valve was sutured to the ascending aorta and two saphenous vein grafts were placed on the proximal coronary arteries. In the other three patients, the composite Woven Dacron graft was used to replace the ascending aorta and two saphenous vein grafts were placed on the distal coronary arteries. One patient died one year postoperatively of LOS because of rapidly progressing coronary grafts ostial stenosis. The other three patients survived and doing well with satisfactory hemodynamic function and no infection. Translocation of the aortic valve for infective aortic valve endocarditis is a useful operative technique when conventional aortic valve replacement technique cannot be utilize.