Biomedical subjects

X X Zhang

Publications and source records attributed to X X Zhang.

At least 37 records · Page 2Linked to original sources

PubMed2001

Giant Hall effect in nonmagnetic granular metal films.

Nearly 3 orders of magnitude enhancement in the Hall coefficient is observed in Cu(x)-(SiO(2))(1--x) granular films. This large enhancement of the Hall coefficient not only is significantly larger than the prediction of the classical percolation theory, but also occurs at a metal concentration identified to be the quantum percolation threshold. Measurements of the electron dephasing length and magnetoresistance, plus the TEM characterization of microstructures, yield a physical picture consistent with the mechanism of the local quantum interference effect.

Journal Article↗

PubMed2001

Dynamic modulation of NMDA-induced responses by ifenprodil in rat prefrontal cortex.

Ifenprodil is known to inhibit channel opening of NMDA receptors containing the NR2B subunit. However, it has also been shown to increase NMDA receptor affinity for glutamate-site agonists, including NMDA. The coexistence of the two opposing effects may explain why ifenprodil can either enhance or suppress an NMDA response depending on the level of NMDA binding and thus the NMDA concentration. Using whole cell recordings in rat prefrontal cortical slices, we report here that the effect of ifenprodil also depends on the speed and the direction of change of NMDA concentration. As shown previously, ifenprodil increased the inward current induced by low concentrations of NMDA applied through a local Y-tube perfusion system. However, the rising phase of the current was less enhanced compared to the falling phase. Increasing the speed of rising of NMDA concentration further reduced the enhancing effect of ifenprodil. When pressure ejection was used to produce even faster NMDA responses, the entire rising phase including the peak of the response was suppressed by ifenprodil, while the falling phase remained enhanced. These results are consistent with the suggestion that ifenprodil decreases both the association and dissociation rates of NMDA from NMDA receptors, and suggest that ifenprodil affects slow and fast NMDA responses in different manners. In particular, this study suggests that ifenprodil inhibits the rising phase of a fast NMDA response by suppressing both channel opening and the association of NMDA with NMDA receptors and that this inhibition can occur even when the level of NMDA binding is low.

Animals↗

PubMed2001

High resolution deletion analysis of constitutional DNA from neurofibromatosis type 2 (NF2) patients using microarray-CGH.

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder whose hallmark is bilateral vestibular schwannoma. It displays a pronounced clinical heterogeneity with mild to severe forms. The NF2 tumor suppressor (merlin/schwannomin) has been cloned and extensively analyzed for mutations in patients with different clinical variants of the disease. Correlation between the type of the NF2 gene mutation and the patient phenotype has been suggested to exist. However, several independent studies have shown that a fraction of NF2 patients with various phenotypes have constitutional deletions that partly or entirely remove one copy of the NF2 gene. The purpose of this study was to examine a 7 Mb interval in the vicinity of the NF2 gene in a large series of NF2 patients in order to determine the frequency and extent of deletions. A total of 116 NF2 patients were analyzed using high-resolution array-comparative genomic hybridization (CGH) on an array covering at least 90% of this region of 22q around the NF2 locus. Deletions, which remove one copy of the entire gene or are predicted to truncate the schwannomin protein, were detected in 8 severe, 10 moderate and 6 mild patients. This result does not support the correlation between the type of mutation affecting the NF2 gene and the disease phenotype. This work also demonstrates the general usefulness of the array-CGH methodology for rapid and comprehensive detection of small (down to 40 kb) heterozygous and/or homozygous deletions occurring in constitutional or tumor-derived DNA.

Adolescent↗

PubMed2001

Trisomy 8 and monosomy 7 detected in bone marrow using primed in situ labeling, fluorescence in situ hybridization, and conventional cytogenetic analyses. A study of 54 cases with hematological disorders.

Trisomy 8 and monosomy 7 are the two most frequent aneuploidies found in hematological disorders such as myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). In this study, primed in situ labeling (PRINS), fluorescence in situ hybridization (FISH) and conventional cytogenetic approaches were used to investigate 54 cases of hematopoietic disorders. Of these cases, there were 22 cases of trisomy 8, 2 cases of tetrasomy 8, 14 cases of monosomy 7, and 16 cases with two copies of both chromosomes 7 and 8. PRINS was carried out in interphase nuclei of bone marrow samples using primers that can specifically detect alpha-satellite DNA sequences of chromosomes 7 and 8. In parallel, using the alpha-satellite probes for chromosomes 7 and 8, FISH was performed for all the cases. PRINS and FISH techniques showed similar specificity and sensitivity. In comparison to FISH, PRINS is more advantageous since it is a faster, easier, and more cost-effective technique. Additionally, for most of the cases, a higher proportion of aneuploidy was detected in metaphases using conventional cytogenetics, as compared to the one found in interphase nuclei identified with PRINS and FISH techniques. In other words, for these cases, the cells with trisomy 8 or monosomy 7, had a distinct proliferative advantage compared to the disomic cell population. Therefore, to better quantify the proportion of aneuploid cells in bone marrow, we recommend to investigate the frequency of aneuploidy in nuclei using PRINS, rather than studying only the dividing cells as detected by conventional cytogenetic techniques.

Adult↗

PubMed2001

Genetic diversity of indigenous Rhizobium leguminosarum bv. viciae isolates nodulating two different host plants during soil restoration with alfalfa.

A total of 360 Rhizobium leguminosarum bv. viciae strains was isolated from three brown-coal mining restoration fields of different age and plant cover (without and in the first and second year of alfalfa, Medicago sativa, cultivation) using two host species (Vicia hirsuta and Pisum sativum) as capture plants. The strains were genetically typed by restriction fragment length polymorphism analysis of polymerase chain reaction (PCR)-generated 16S-23S ribosomal DNA intergenic spacer regions (IGS-RFLP) and characterized by plasmid profiles and RFLP analysis of amplified nodABC genes. The R. leguminosarum bv. viciae population was dominated by the same group of strains (irrespective of the trap plant used). According to type richness, the genetic diversity of indigenous R. leguminosarum in the second year of restoration was lower than in the first year and it resembled that of the fallow field, except for plasmid types, in which it was higher than that of the fallow field. Some of the less frequent nodABC genotypes were associated with distinct chromosomal IGS genotypes and symbiotic plasmids (pSyms) of different sizes, indicating that horizontal transfer and rearrangements of pSym can occur in natural environments. However, the dominant pSym and chromosomal genotypes were strictly correlated suggesting a genetically stable persistence of the prevailing R. leguminosarum bv. viciae genotypes in the absence of its host plant.

DNA, Bacterial↗

PubMed2001

Symbiotic plasmid rearrangement in Rhizobium leguminosarum bv. viciae VF39SM.

A rearrangement between the symbiotic plasmid (pRleVF39d) and a nonsymbiotic plasmid (pRleVF39b) in Rhizobium leguminosarum bv. viciae VF39 was observed. The rearranged derivative showed the same plasmid profile as its parent strain, but hybridization to nod, fix, and nif genes indicated that most of the symbiotic genes were now present on a plasmid corresponding in size to pRleVF39b instead of pRleVF39d. On the other hand, some DNA fragments originating from pRleVF39b now hybridized to the plasmid band at the position of pRleVF39d. These results suggest that a reciprocal but unequal DNA exchange between the two plasmids had occurred.

Nucleic Acid Hybridization↗

PubMed2001

[NADPH-diaphorase activity and Fos expression in brainstem nuclei involved in cardiovascular regulation following intracarotid injection of capsaicin].

The present study was undertaken to define whether intracarotid injection of capsaicin induces Fos expression associated with the activation of NOS-containing neurons in brainstem nuclei by combining the immunocytochemical method for Fos with NADPH-d histochemical technique for NOS. The results obtained are as follows: (1) Intracarotid injection of capsaicin caused a significant increase of Fos-like immunoreactive neurons in area postrema (AP), nucleus tractus solitarius (NTS), paragigantocellularis lateralis (PGL) and locus coeruleus (LC), without influence upon the neurons of raphe nuclei (RN) and periaqueductal gray (PAG). (2) NO-containing neurons in PGL and NTS and the double-labeled neurons in PGL were also increased significantly following intracarotid injection of capsaicin. Small numbers of NO-containing neurons were found in LC, but there was no change in the number of NO-containing neurons in RN and PAG. No NADPH-d histochemical activity could be found in AP. (3) The above responses to capsaicin were significantly inhibited by pretreatment with either a capsaicin receptor antagonist ruthenium red or a NMDA receptor antagonist MK-801. The above results indicate that intracarotid injection of capsaicin may activate the neurons in brainstem nuclei involved in cardiovascular regulation, and that NO only plays an indirect role in the modulation of the responses of brainstem nuclei to capsaicin. These effects of capsaicin are mediated by capsaicin receptors with involvement of glutamate.

Animals↗

PubMed2001

Renal ischemia enhances electrical activity and Fos protein expression of the rostral ventrolateral medullary neurons in rats.

The effects of renal ischemia on spontaneous electrical activity and Fos protein expression of nucleus paragigantocellularis lateralis (PGL) in rostral ventrolateral medulla (RVLM) were observed in 67 anesthetized Sprague-Dawley rats with sinoaortic denervation by using extracellular recording and immunohistochemical techniques. The results obtained are as follows. (1) Renal ischemia increased the discharge rate from 11.40 +/- 1.08 to 21.1 +/- 1.74 spikes/s (P < 0.001) in 28 out of 30 PGL neurons, while blood pressure and heart rate had no significant change (P > 0.05). (2) Administration of 8-phenyltheophylline (8-PT), an adenosine receptor antagonist, did not affect the discharge rate of PGL neurons, but could partially inhibit the effects of renal ischemia in 17 units (P < 0.05). (3) Renal ischemia resulted in a remarkable increase in the number of Fos-like protein immunoreactive PGL neurons in the RVLM (P < 0.01). (4) Fos protein expression induced by renal ischemia was significantly inhibited by pretreatment with 8-PT (P < 0.05). Taken together, it is concluded that renal ischemia induces an increase in spontaneous electrical activity and Fos protein expression in PGL neurons of RVLM, and that adenosine released within ischemic kidney may be involved in such effects.

Animals↗

PubMed2001

[Important bio-thermal physical problems and latest advancement in laser cell engineering].

The recently emerging technique of laser microsurgery (optical tweezers, optical scissors, etc.) is providing a new precise, sterile method for the cell engineering practices such as introduction of external gene into an object cell, cell-fusion, and trapping or transportation of microscopic objects (cells or chromosomes etc.). The thermal effects thus induced usually proved to be critical factors for successful operation of this method. In order to meet the requirement for the rapid development in this territory, some important bio-thermal physical problems and the corresponding research subjects in this area were comprehensively summarized. Difficulties and critical issues were discussed. The latest advancement of the laser cell engineering was also described. This review is attempted to bridge up the gap between bioengineering and thermal science fields and then to enhance the rapid progress of laser microsurgery.

Biotechnology↗

PubMed2000

Sterically demanding diporphyrin ligands and rhodium(II) porphyrin bimetalloradical complexes.

A series of sterically demanding diporphyrins H2(por)-X-(por)H2 ligands that contain spacers (X) with different degrees of flexibility were synthesized from the trimesitylporphyrin derivatives 5-(4-hydroxyphenyl)-10,15,20-trimesitylporphyrin (TMP-OH)H2 (1a) and 5-(2,6-dimethyl-4-hydroxyphenyl)-10,15,20-trimesityl-porphyrin, (DMTMP-OH)H2 (1b). The monomeric porphyrins 1a,b, which have steric demands similar to that of tetramesitylporphyrin, (TMP)H2, and carry a hydroxyl functional group at the para position of one of the mesophenyl substituents, were constructed from reaction of pyrrole with two aromatic aldehydes by a mixed aldehyde condensation approach. The diporphyrins with alkyl diether tethers were obtained stepwise from reactions of the hydroxy functionalized porphyrins 1a,b with dibromides Br(CH2)nBr. The diporphyrin which contains a more rigid m-xylylene spacer, was made directly from reaction of 1b with alpha,alpha'-dibromo-m-xylene. Rhodium was inserted into the porphyrins using Rh2(CO)2Cl2 and converted to dimethyl complexes Me-Rh(Por)-X-(Por)Rh-Me. The dirhodium(II) derivatives .Rh(por)-X-(por)Rh.) were generated by photolysis of the dimethyl complexes and observed to occur as stable bimetalloradicals because the ligand steric demands prohibit Rh(II)-Rh(II) bonding. EPR spectra of the dirhodium(II) derivatives, triphenyl phospine adducts, and dioxygen complexes are reported. The kinetic advantage of bimetalloradical complexes for substrate reactions that have two metal-centered radicals in the transition state is demonstrated by reactions of dihydrogen with dirhodium(II) bimetalloradical complexes.

Journal Article↗

PubMed2000

Determination of morphine by capillary electrophoresis immunoassay in thermally reversible hydrogel-modified buffer and laser-induced fluorescence detection.

In this paper thermally reversible hydrogel used as a replaceable packed material for capillary electrophoresis was examined. A simple and rapid method of detecting morphine was developed, which demonstrated the potential of strong affinity antibodies as a selector for immunologically-based separations in serum by capillary electrophoresis. Polyclonal antibodies were linked to hydrogel and applied to the separation of free fluorescein isothiocyanate (FITC)-labeled antigen and bound FITC antigen. The separation was monitored with laser-induced fluorescence detection. Different separation conditions were studied. The results indicated that poly-N-isopropylacrylamide hydrogel (PNIPA) is a kind of steady, replaceable gel. The specific determination of morphine did not require a long incubation time and PNIPA hydrogel-modified antibodies can be stockpiled at 4 degrees C before assay. It can be used to determine morphine with good precision and a detection limit lower than 8.5 ng/ml. Details of the preparation of hydrogel cross-linked polyclonal antibody and of typical separations of bound and free antigen are presented.

Antibody Specificity↗

PubMed2000

Synthesis of PDK, a novel porphyrin-linked dicarboxylate ligand.

A novel trinucleating ligand system H4(PDK), for porphyrin-based diamine bis(Kemp's triacid)imide, was constructed by using two molecules of Kemp's triacid and one molecule of porphyrin as building blocks. The dimeso-substituted octaalkylporphyrin unit, carrying bromomethyl groups at the ortho positions of two trans-positioned meso-phenyl groups, was synthesized from (3,3'-diethyl-4,4'-dimethyl-2,2'-dipyrrolyl)methane and (alpha-bromo-o-tolualdehyde. The structures of both of the two atropisomers (alpha,alpha- and alpha,beta-) of bromoporphyrin, H2(alpha,alpha-BP) and H2(alpha,beta-BP), were determined by X-ray crystallography, with the alpha,beta-isomer as the free base form and the alpha,alpha-isomer as the zinc complex. Both the alpha,alpha- and alpha,beta-isomers of the bromomethyl porphyrins were converted to their aminomethyl derivatives, H2(alpha,alpha-AP) and H2(alpha,beta-AP), through the corresponding imidoporphyrin intermediates, H2(alpha,alpha-IP) and H2(alpha,beta-IP), by the Gabriel synthesis. The alpha,alpha- and alpha,beta-aminoporphyrins were coupled with Kemp's triacid anhydride-chloride to form H4(alpha,alpha-PDK) and H4(alpha,beta-PDK), respectively. Unlike the alpha,beta-isomer, the structure of which was determined by X-ray crystallography for the zinc complex, H4(alpha,alpha-PDK) has a remarkable and complicated solvent-dependent 1H NMR spectrum that suggests the existence of hydrogen bonding interactions between two convergent, tethered Kemp's triacid units, as predicted in a modeling study. The convergent feature is essential for the target ligand H4(alpha,alpha-PDK) to form trinuclear metal complexes with a bis(carboxylato) dimetallic unit sitting above a metalloporphyrin ring.

Dicarboxylic Acids↗

PubMed2000

Structures and magnetism of two novel heptanuclear lanthanide-centered trigonal prismatic clusters: [LnCu6(mu 3-OH)3(HL)2(L)4](ClO4)2.25H2O (Ln = La, Tb; H2L = iminodiacetic acid).

The new heteronuclear iminodiacetic acid (H2L) complexes [LnCu6(mu 3-OH)3(HL)2(L)4](ClO4)(2).25H2O with Ln = La (1) and Tb (2) have been prepared in aqueous solution and characterized by single-crystal X-ray diffraction to be isomorphous (crystallographic data for 1 and 2: hexagonal, P63/m; a = b = 12.6425(14) A, c = 24.541(5) A, Z = 2 (1); a = b = 12.5802(9) A, c = 24.285(4) A, Z = 2 (2)). Ln3+ was found to be located in the center of the trigonal prismatic cage formed by six Cu2+ ions, with a tricapped trigonal prismatic coordination environment of nine O atoms. The magnetic properties of complexes 1 and 2 have been studied. The results indicate the presence of ferromagnetic couplings between Tb3+ and Cu2+ in compound 2.

Journal Article↗

PubMed2000

Dual effects of D-amphetamine on dopamine neurons mediated by dopamine and nondopamine receptors.

By increasing dopamine (DA) release and activating feedback mechanisms, amphetamine and related psychostimulants are known to inhibit DA cell firing. Here, we report that D-amphetamine also has an excitatory effect on DA cells, which under control conditions, is masked by the inhibitory effect of D-amphetamine and is revealed when D2-like receptors are blocked. Thus, using in vivo single-unit recording in rats, we found that the selective D2 antagonist raclopride not only blocked the inhibition induced by D-amphetamine but also enabled D-amphetamine to excite DA cells. The excitation, expressed as an increase in both firing rate and bursting, persisted when both D1- and D2-like receptors were blocked by SCH23390 and eticlopride, suggesting that it is not mediated by DA receptors. The norepinephrine uptake blocker nisoxetine mimicked the effect of D-amphetamine, especially the increase in bursting, whereas the 5-HT uptake blocker fluoxetine produced no significant effect. Adrenergic alpha1 antagonists prazosin and WB4101 and the nonselective alpha antagonist phenoxybenzamine completely blocked increase in bursting induced by D-amphetamine and partially blocked the increase in firing rate. The alpha2 antagonist idazoxan and the beta antagonist propranolole, however, failed to prevent D-amphetamine from producing the excitation. Thus, revising the traditional concept, this study suggests that D-amphetamine has two effects on DA cells, a DA-mediated inhibition and a non-DA-mediated excitation. The latter is mediated in part through adrenergic alpha1 receptors.

Action Potentials↗

PubMed2000

Tetrasomy 8 evolving into a segmental triplication 8q in a case of acute monocytic leukemia.

We report a case of AML-M5 with tetrasomy 8 that evolved within a 7-month period to a segmental triplication 8q. Other numerical abnormalities in the initial diagnosis were not found at the relapse; however, a chromosome 1 structural abnormality was maintained, proving the clonal evolution from tetrasomy 8 to a segmental triplication of the long arm of 8. This strongly suggests that there is a functional and selective advantage for duplications and triplications of 8q in these patients.

Aged↗

PubMed2000

Enhancement of NMDA-induced current by the putative NR2B selective antagonist ifenprodil.

Ifenprodil has been widely used as an antagonist selective for NMDA receptors containing the NR2B subunit. Evidence suggests, however, that ifenprodil also increases NMDA receptor affinity. Using rat brain slices, we found that ifenprodil enhanced NMDA-induced current in both cortical and subcortical areas examined. To test whether the effect is due to an increase in NMDA receptor affinity, we compared the effect of ifenprodil on currents induced by different concentrations of NMDA. Consistent with the hypothesis, the enhancing effect (percent increase) was relatively constant at low NMDA concentrations. As NMDA concentration increased, however, the effect decreased. To test whether the effect is blocked when NMDA binding sites are saturated with NMDA, high concentrations of NMDA were applied. To partially block Ca(2+) influx and prevent cells from deteriorating, the experiments were performed in the presence of either MK801 or kynurenate, two noncompetitive antagonists. Under such conditions, ifenprodil not only failed to potentiate NMDA currents, but consistently suppressed the current. When the same concentration of NMDA was applied in the presence of the competitive antagonist CGP37849, ifenprodil regained its ability to potentiate NMDA currents. Furthermore, the higher the concentration of CGP37849 the more the NMDA current was potentiated by ifenprodil. These results, combined with previous studies, suggest that the enhancing effect is due to an increase in NMDA receptor affinity and is specific for responses induced by low NMDA concentrations. As NMDA concentration increases, the affinity-enhancing effect decreases. Consequently, the channel-suppressing effect becomes more prominent.

2-Amino-5-phosphonovalerate↗

PubMed2000

Increased incidence of trisomy 8 in acute myeloid leukemia with skin infiltration (leukemia cutis).

Anecdotal literature reports and the authors' own observations suggest an association between chromosome 8 aneuploidy and leukemia cutis. The authors investigated this potential association by using fluorescence in situ hybridization (FISH) directly on skin infiltrates in a series of 11 patients with acute monocytic leukemia (AML). Seven of the 11 patients were aneuploid for chromosome 8 by FISH which was confirmed by dual color hybridization. Six of these seven patients were AML-M4 or M5 and one was M1. The majority of the cases with leukemia cutis expressed CD4 (90% of cases), CD14 (60%), and/or CD56 (50%) in bone marrow leukemic cells. The data show the utility of examination of skin infiltrates by FISH for the detection of trisomy 8 in leukemia cutis. They also suggest the importance of trisomy 8 as a factor in predisposition to skin infiltration in AML.

Chromosomes, Human, Pair 8↗

PubMed2000

The common nodulation genes of Astragalus sinicus rhizobia are conserved despite chromosomal diversity.

The nodulation genes of Mesorhizobium sp. (Astragalus sinicus) strain 7653R were cloned by functional complementation of Sinorhizobium meliloti nod mutants. The common nod genes, nodD, nodA, and nodBC, were identified by heterologous hybridization and sequence analysis. The nodA gene was found to be separated from nodBC by approximately 22 kb and was divergently transcribed. The 2. 0-kb nodDBC region was amplified by PCR from 24 rhizobial strains nodulating A. sinicus, which represented different chromosomal genotypes and geographic origins. No polymorphism was found in the size of PCR products, suggesting that the separation of nodA from nodBC is a common feature of A. sinicus rhizobia. Sequence analysis of the PCR-amplified nodA gene indicated that seven strains representing different 16S and 23S ribosomal DNA genotypes had identical nodA sequences. These data indicate that, whereas microsymbionts of A. sinicus exhibit chromosomal diversity, their nodulation genes are conserved, supporting the hypothesis of horizontal transfer of nod genes among diverse recipient bacteria.

Acyltransferases↗