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Y Z Xu

Publications and source records attributed to Y Z Xu.

At least 19 recordsLinked to original sources
PubMed2003

Stress-induced birefringence control in optical planar waveguides.

For what is to our knowledge the first time, the thermal-stress formula in analytical form is derived for the core layer in an optical planar waveguide by the thin-film approximation, which is based on a closed-form solution in multilayered isotropic structures off the edges. This formula indicates that elastic, thermal, and structural parameters can affect the magnitude of the stress. Using the formula, one can remove thermal stress and hence stress-induced birefringence by proper waveguide design.

Journal Article↗
PubMed2001

Photoactivation of DNA thiobases as a potential novel therapeutic option.

The thiopurines, 6-thioguanine and 6-mercaptopurine, are antileukemic agents that are incorporated into DNA following retrieval by the purine salvage pathway (see [1] for a review). Their toxicity requires active DNA mismatch repair (MMR), and thiopurine resistance is an acknowledged phenotype of MMR-defective cells [2, 3]. In addition to these direct cytotoxic effects, DNA thiobases have distinctive photochemical properties [4], the therapeutic potential of which has not been extensively evaluated. We report here that the thiopyrimidine nucleoside 4-thiothymidine is incorporated into DNA. It does not induce MMR-related toxicity, but it interacts synergistically with UVA light and dramatically sensitizes cultured human cells to very low, nonlethal UVA doses. 4-thiothymidine induced UVA dose enhancements of around 100-fold in DNA repair-proficient cells. Nucleotide excision repair-defective xeroderma pigmentosum cells were sensitized up to 1000-fold, implicating bulky DNA photoproducts in the lethal effect. The synergistic action of thiothymidine plus UVA required thymidine kinase, indicating a selective toxicity toward rapidly proliferating cells. Cooperative UVA cytotoxicity is a general property of DNA thiobases, and 6-thioguanine and 4-thiodeoxyuridine were also UVA sensitizers. Thiobase/UVA treatment may offer a novel therapeutic approach for the clinical management of nonmalignant conditions like psoriasis or for superficial tumors that are accessible to phototherapy.

Cell Line↗
PubMed2001

Vasopressin reverses aluminum-induced impairment of synaptic plasticity in the rat dentate gyrus in vivo.

Aluminum (Al), an important neurotoxin, contributes to a variety of cognitive dysfunction and mental diseases. Previous studies have demonstrated that Al impairs hippocampal long-term potentiation (LTP) in vitro and in vivo. In the present study, both LTP and LTD (long-term depression) were recorded in the same animal to investigate the Al-induced impairment of synaptic plasticity. Another aim of the present research was to verify whether the impairment of synaptic plasticity induced by Al could be reversed by vasopressin (VP) treatment. Neonatal Wistar rats were exposed to Al from parturition through adulthood (pre- and post-weaning) by the drinking of 0.3% aluminum chloride (AlCl(3)) solution. The input-output (I/O) function, paired-pulse reaction (PPR), excitatory postsynaptic potential (EPSP) and population spike (PS) amplitude were measured in the dentate gyrus (DG) of adult rats (60-90 days) in response to stimulation applied to the lateral perforant path. The results showed: (1) Al reduced the amplitudes of both EPSP LTP (control: 132+/-7%, n=7; Al-exposed: 115+/-10%, n=8, P<0.05) and PS LTP (control: 242+/-18%, n=7; Al-exposed: 136+/-7%, n=8, P<0.01) significantly. The amplitudes of EPSP LTD (control: 82+/-6%, n=7; Al-exposed: 92+/-7%, n=8, P<0.05) and PS LTD (control: 81+/-4%, n=7; Al-exposed: 98+/-5%, n=8, P<0.05) were also decreased by Al treatment. The Al-induced impairments of PS LTP and PS LTD were more serious than that of EPSP LTP and EPSP LTD. (2) In control rats, VP had an increase in the PS LTP amplitude (control: 242+/-18%, n=7; control+VP: 358+/-23%, n=6, P<0.01), while it had no significant effects on PS LTD (control: 81+/-4%, n=7; control+VP: 76+/-7%, n=6, P>0.05). (3) In Al-exposed rats, VP had a significant increase in the amplitudes of both PS LTP (Al-exposed: 136+/-7%, n=8, Al-exposed+VP: 255+/-16%, n=6, P<0.01) and PS LTD (Al-exposed: 98+/-5%, n=8; Al-exposed+VP: 81+/-6%, n=6, P<0.05). After the application of VP, the range of synaptic plasticity (PS LTP+PS LTD) in Al-exposed rats increased from 38% to 174%, which surpassed that in control rats (161%). It was suggested that VP could reverse Al-induced impairment of synaptic plasticity and might be an effective medicine to cure Al-induced neurological disorders.

Aluminum Chloride↗
PubMed2001

Unlike 2-deoxy-D-glucose, 3-O-methyl-D-glucose does not induce long-term potentiation in rat hippocampal slices.

Equimolar replacement of 10 mM glucose by 2-deoxy-D-glucose (2-DG) causes substantial depression followed by a sharp and sustained potentiation of CA1 field EPSPs. In the present experiments, similar applications of 3-O-methyl-D-glucose, which is also taken up by cells but is not phosphorylated, had only a weak blocking action and elicited no potentiation. Possible explanations for the marked effects of 2-DG include a more rapid block of glycolysis and the production of phosphorylated derivatives of 2-DG.

3-O-Methylglucose↗
PubMed2001

Distinguishing malignant from normal oral tissues using FTIR fiber-optic techniques.

Oral tissue samples were studied using mid-IR fiber-optic attenuated total reflectance spectroscopy and other spectral techniques. The 1745 cm(-1) band, which is assigned to the ester group (C==O) vibration of triglycerides, is a reliable marker that is present in normal tissues but absent or a weak band in malignant oral tissues. Other bands such as C--H stretching bands and the amide bands are also helpful in distinguishing malignant tissues from normal tissues. Subtraction spectra confirmed the above conclusion. In addition, Raman spectroscopic measurements were in agreement with the results observed from FTIR spectra.

Biomarkers, Tumor↗
PubMed2001

Dichloro(2,2'-diamino-4,4'-bi-1,3-thiazole-N3,N3')copper(II).

The title complex, [CuCl(2)(C(6)H(6)N(4)S(2))], has a flattened tetrahedral coordination. The Cu(II) atom is located on a twofold rotation axis and is coordinated by two N atoms from a chelating 2,2'-diamino-4,4'-bi-1,3-thiazole ligand and by two Cl atoms. Intramolecular hydrogen bonding exists between the amino groups of the 2,2'-diamino-4,4'-bi-1,3-thiazole ligand and the Cl atoms. The intermolecular separation of 3.425 (1) A between parallel bithiazole rings suggests there is a pi-pi interaction between them.

Journal Article↗
PubMed2001

Enhanced continent mechanism of tapered ileum by extramural support from the pouch and abdominal walls: a preliminary report of a clinical study.

PURPOSE: We constructed a reliable continent tube that is easy to catheterize and surgically simple. MATERIALS AND METHODS: Eight patients with bladder cancer underwent a procedure in which ileal segment was tapered as an efferent tube, of which a part was placed between the back surface of the rectus muscle and the ileal pouch wall. The internal orifice of the tapered ileum was anastomosed to the ileal pouch and its external orifice was anastomosed to the umbilicus. Urodynamic and radiological studies were done postoperatively in 7 cases. RESULTS: The stoma was easily catheterized with a 16Fr catheter in all cases. One patient died of heart disease 55 days postoperatively, while 6 of the remaining 7 were completely continent day and night. Urodynamic study of the efferent tubes showed that maximum close pressure with the pouch full was significantly higher than with the pouch empty (p <0.001). Retrograde radiography of the efferent tubes demonstrated perfect canalization without stenosis. CONCLUSIONS: This study indicates that the continent mechanism of tapered ileum may be greatly enhanced by fixing it between the abdominal and pouch walls. This maneuver also provides easy catheterization and surgical simplicity.

Abdominal Muscles↗
PubMed2001

[Energy transfer between electric polymer PVK and terbium complex and its transmission electronmicroscope (TME) study].

A chloroform-soluble terbium complex, which is confirmed to be Tb(aspirin)3 phen using element analysis and FT-IR spectroscopy, was synthesized. Photoluminescent investigation on the terbium complex and PVK-terbium complex composite was conducted. Förster energy transfer occurred between the terbium complex and the PVK matrix. There are no overlap between UV spectrum of the complex and the emission spectrum of PVK, however, overlap is observed between the excitation spectrum of the complex and the emission spectrum of PVK. Therefore, we suggest that the necessary condition of Förster energy transfer should be overlap between the excitation (not UV) spectrum of one complex and the emission spectrum of polymer matrix. Further investigation indicates that the emission of PVK can be suppressed at different extents by doping various amount of Tb(aspirin)3 phen into PVK films. The ratio of Tb(aspirin)3 phen: PVK = 1:2 (wt%) are regarded as an optimized ratio for limiting the emission of PVK. TEM images of PVK/Tb(aspirin)3 phen films reveal that nanoparticles of the Tb complex are dispersed in the PVK matrix. The size of the aggregated complex in PVK matrix is 20-30 nm. The film is not homogeneous as dark regions co-exist with light region in the TEM images. This phenomenon may be related to the short lifetime of electroluminescent devices.

Chelating Agents↗
PubMed2000

Sugar interaction with metal ions. FT-IR study on the structure of crystalline galactaric acid and its K+, NH4+, Ca2+, Ba2+, and La3+ complexes.

The FT-IR spectra of galactaric acid and its K+, NH4+, Ca2+, Ba2+, and La3+ salts have been recorded and interpreted. Spectroscopic evidence shows that the dimeric carboxylic groups of the free acid are dissociated upon formation of the salt, and the asymmetric and symmetric stretching vibrations of the anionic COO- group in these salts are observed at about 1600 and 1400 cm-1, respectively. The two carboxylic groups of the galactarate coordinate with Ca2+ ions in a monodentate form. One of the carboxylic groups in the Ba2+ salt coordinates in a monodentate state; another group interacts with three cations in a tetradentate form. In the K+, NH4+, and La3+ salts, the COO- groups coordinate in a polydentate manner with the cations. By comparison of the spectra of the salts with that of the free acid, it is concluded that the hydroxyl groups of the galactarate skeleton take part in metal-oxygen interaction, and the hydrogen-bonding network is rearranged upon sugar metalation. The degree of participation of the sugar OH groups in metal-galactarate interaction is varied from the K+ and NH4+ salts to the Ca2+, Ba2+, and La3+ salts.

Barium↗
PubMed2000

Effects of chronic lead exposure on short-term and long-term depression in area CA1 of the rat hippocampus in vivo.

Chronic developmental lead (Pb) exposure to the rat has been reported to impair the long-term potentiation (LTP) in area CA1 and DG of the hippocampus. The present study was performed to investigate the effects of chronic Pb exposure on homosynaptic short-term depression (STD) and long-term depression (LTD) of population spikes (PS) in area CA1 of the rat hippocampus in vivo. Neonatal Wistar rats were exposed to Pb from parturition to weaning via the milk of dams fed with 0.2% lead acetate solution. The input/output (I/O) function, paired-pulse reaction (PPR), the PS were measured in the area CA1 in response to low frequency stimulation (LFS). The results showed that the homo-STD amplitude of PS depotentiation in Pb-exposed rats (87.48 +/- 7.44%, n = 14) was less significant than that in control rats (72.34 +/- 6.05%, n = 18, P<0.05), and the homo-LTD amplitude of PS depotentiation in Pb-exposed rats (72.80 +/- 5.86%, n = 14) was even less significant than that in control rats (47.80 +/- 5.03%, n = 18, P<0.01). The results suggest that chronic Pb exposure in neonatal rats caused impairments in the STD and LTD of area CA1 of hippocampus.

Animals↗
PubMed2000

Effects of the active aldehyde group generated by RNA N-glycosidase in the sarcin/ricin domain of rat 28S ribosomal RNA on peptide elongation.

Effects of the active aldehyde group of ribose C1' at position 4324 of rat 28S rRNA, in the inactivated ribosome generated by RNA N-glycosidases (trichosanthin, A-chain of cinnamomin and ricin), on peptide elongation have been studied. The aldehyde group inhibits the activities of eEF1A-dependent aminoacyl-tRNA binding to the inactivated ribosome and eEF1A-dependent GTPase, but increases eEF2-dependent activity. At a high concentration of RNA N-glycosidase, the generated aldehyde group also inhibits aminoacyl-tRNA binding to the inactivated ribosome in the absence of elongation factor and translocation activity. When the aldehyde group is reduced into a hydroxyl group by sodium borohydride or blocked with an amino acid through nucleophilic addition, the activities of eEF1A-dependent aminoacyl-tRNA binding and eEF1A-dependent GTPase of the inactivated ribosome are partially restored, but the altered activities of eEF2-dependent GTPase, translocation and aminoacyl-tRNA binding in the absence of elongation factor are not normalized. Thus, reduction or blockage of the aldehyde group with sodium borohydride or amino acids might change the conformation of the S/R domain in rat 28S ribosomal RNA to meet the requirement for eEF1A-dependent reactions, but not eEF2-involved reactions.

Aldehydes↗
PubMed2000

[Implementation of a software for acquiring and analysing myoelectric potential signals in ergonomical research of space manual system].

Objective. A software used for acquiring and analyzing signals was developed for ergonomical research on Human Workload in space manual system. Method. As an important part of the whole experimental equipment and being developed in PC, the software is composed of acquisition and display program, analysis and processing program and data files. Result. The software is capable of making realtime acquisition and display of four channels of myoelectric potential signals and one channel of operation signal synchronously. The signals are then analyzed and processed off-line. Conclusion. During the development, its realtime feature was implemented by means of some technical methods, such as that different machine assigned to view-scenery display and signal acquisition, different frequency assigned to EMG signal and operation ones, and different cycle assigned to acquisition, display and storage. Above all, with friendly man-machine interface and high accuracy of data, the software was even reliable.

Data Display↗
PubMed1999

The effects of chronic lead exposure on long-term depression in area CA1 and dentate gyrus of rat hippocampus in vitro.

Long-term potentiation (LTP) and long-term depression (LTD), two forms of synaptic plasticity, are believed to underlie the mechanisms of learning and memory. Previous studies have demonstrated that low-level lead exposure can impair the induction and maintenance of LTP in vivo and in vitro. The present study was carried out to investigate whether the low-level lead exposure affected the induction and maintenance of LTD. Neonatal Wistar rats were exposed to lead from parturition to weaning via milk of dams drinking 0.2% lead acetate solution. Field excitatory postsynaptic potentials (EPSPs) were recorded in hippocampal slices in adult rats (50-65 days) to study the alterations of LTD in area CA1 and dentate gyrus (DG) of hippocampus following chronic lead exposure. The input-output (I/O) curves before conditioning in both areas showed no evident alterations in basic synaptic transmission between the control and lead exposure groups. In area CA1, the mean amplitude of EPSP slope in control rats (61+/-11%, n=15) decreased significantly greater than that in lead-exposed rats (78+/-8%, n=8, P<0.05) following low frequency stimulation (LFS, 1 Hz, 15 min), which lasted at least 45 min. In area DG, with application of the same LFS, the LTD was induced in control rats (72+/-22%, n=8), while the LFS failed to induce LTD in lead-exposed rats (100+/-26%, n=8). These results showed that chronic lead exposure affected the induction of LTD in both area CA1 and DG. The effect of lead on synaptic plasticity in area CA1 was also investigated. The alteration of the amplitude of LTP in hippocampal slices caused by lead was reexamined in order to compare with that on LTD (control: 189+/-23, n=5; lead-exposed: 122+/-12, n=10). The result demonstrated that low-level lead exposure could reduce the range of synaptic plasticity, which might underlie the dysfunction of learning and memory caused by chronic lead exposure.

Animals↗
PubMed1999

Biological effects of rare earth protein complexes: influence of lanthanide ions Eu3+, Tb3+ on secondary structure of calmodulins.

The secondary structure of four kinds of calmodulins (CaMs; i.e., Brassica campestris pollen CaM, bovine brain CaM, earthworm calcium binding protein, and earthworm new calcium binding protein) in thin films are determined by the FTIR resolution enhanced technique and curve fitting. The variation in the secondary structure of CaM upon its binding with Ca2+, Eu3+, and Tb3+, the assay of phosphodiesterase enzyme, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis are also investigated. The effect of lanthanide ions on the conformation of CaM are described.

Animals↗
PubMed1999

Purification and characterization of trichomaglin--a novel ribosome-inactivating protein with abortifacient activity.

Trichomaglin, a novel ribosome-inactivating protein, has been isolated from root tuber of a plant Maganlin (Trichosanthes Lepiniate, Cucurbitaceae). The isolation and purification procedure included ammonium sulfate precipitation, Sephadex G-75 chromatography and CM-Sephadex C-50 chromatography. The protein was identified to be homogeneous by SDS-PAGE and FPLC analysis. Its molecular weight is 24,673 dalton and isoelectric point is 5.8, determined by electrospray ionization mass spectroscopy and isoelectric focusing gel electrophoresis respectively. Trichomaglin can inhibit protein synthesis in rabbit reticulocyte lysate with ID50 of 10.1 nM. When rat ribosome was incubated with trichomaglin, a diagnostic RNA fragment appeared on polyacrylamide gel after ribosomal RNAs were treated with acidic aniline. It was concluded that trichomaglin is an RNA N-glycosidase. In addition, it has been verified to be an abortifacient protein.

Abortifacient Agents, Nonsteroidal↗
PubMed1999

The cytotoxicity of DNA carboxymethylation and methylation by the model carboxymethylating agent azaserine in human cells.

Carboxymethylating agents are potential sources of endogenous DNA damage that have been proposed as possible contributors to gastrointestinal carcinogenesis. The cytotoxicity of the model DNA carboxymethylating agent azaserine was investigated in human cells. Expression of the DNA repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT) did not affect sensitivity to the drug in two related Raji Burkitt's lymphoma cell lines. DNA mismatch repair-defective variants of Raji cells which display increased tolerance to DNA methylation damage were not selectively resistant to azaserine. Complementary results were obtained with a second carboxymethylating agent, potassium diazoacetate. In contrast, lymphoblastoid cell lines representative of each of the xeroderma pigmentosum complementation groups, including the variant, were all significantly more sensitive to azaserine than nucleotide excision repair-proficient cells. The hypersensitivity of XP cells was not due to systematic differences in the concentrations of intracellular thiol compounds or related thiol metabolizing enzymes. The data indicate that of the two types of potentially lethal DNA damage which azaserine introduces, carboxymethylated bases and O(6)-methylguanine, the former are repaired by nucleotide excision repair and are a more significant contributor to azaserine lethality in human cells.

Adenine↗
PubMed1998

Impairment of long-term potentiation and paired-pulse facilitation in rat hippocampal dentate gyrus following developmental lead exposure in vivo.

Neonatal rats were exposed to lead from parturition to weaning via the milk of dams drinking 0.2% lead acetate solution. The alterations of long-term potentiation (LTP) and paired-pulse facilitation (PPF) of hippocampal dentate gyrus in adult rats (90-115 days) following developmental lead exposure were studied in vivo. Input/output (I/O) function, paired-pulse facilitation (PPF), excitatory postsynaptic potential (EPSP) and population spike (PS) amplitude were measured in the dentate gyrus (DG) in response to stimulation applied to the lateral perforant path. The results showed that LTP was induced in control rats with an average PS potentiation of 321.1+/-50.0% (n=18), which was significantly greater than the increase in PS potentiation (173.5+/-30.0%, n=17, p<0.001) in lead-exposed rats after tetanizing stimulation. The mean EPSP potentiation increased to 172.4+/-27.0% (n=18) in control and 138.8+/-21.4% (n=17) in lead-exposed rats after tetanizing stimulation. The lead-induced impairment of LTP of PS potentiation was more serious than that of EPSP potentiation. Following pairs stimulation of perforant fiber at 250 microA and an interpulse interval (IPI) of 10-1000 ms, the average peak facilitation of PS was 211.3+/-25.0% (n=13) in control and 187.7+/-23.0% (n=11) in lead-exposed rats. The average facilitation period duration of PS was 243.0+/-35.8 ms (n=13) in control and 138.0+/-24.4 ms (n=11) in lead-exposed rats. These results suggested that developmental lead exposure in neonatal rats caused impairments in LTP and PPF of hippocampal dentate gyrus.

Animals↗