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C Chen

Publications and source records attributed to C Chen.

At least 325 records · Page 18Linked to original sources
PubMed2000

Unique chromosome identification and sequence-specific structural analysis with short PNA oligomers.

We have extended our earlier work to show that individual 14-20mer peptide nucleic acid probes directed against interspersed alpha-satellite sequences can specifically identify chromosomes. Peptide nucleic acid (PNA) probes were used to detect chromosomal abnormalities and repeat structure in the human genome by fluorescence in situ hybridization (FISH). The hybridization of a single PNA probe species directed against a highly abundant alpha-satellite DNA repeat sequence was sufficient to absolutely identify a chromosome. Selection of highly repetitive or region-specific DNA repeats involved DNA database analysis. Distribution of a specific repeat sequence in human genome was estimated through two means: a computer program "whole genome" approach based on approximately 400 Mb (12%) human genomic sequence. The other method involved directed search for alpha satellite sequences. In total, approximately 240 unique DNA repeat candidates were found. Forty-two PNA probes were designed for screening chromosome-specific probes. Ten chromosome-specific PNA probes for human Chromosomes (Chrs) 1, 2, 7, 9, 11, 17, 18, X, and Y have been identified. Interphase and metaphase results demonstrate that chromosome-specific PNA probes are capable of detecting simple aneuploidies (trisomies) in human. Another set of PNA probes showed distinct banding-like patterns and could be used as sequence-specific stains for chromosome "bar coding". Potential application of PNA probes for investigating repeat structure and function is also discussed.

Base Sequence↗
PubMed2000

Detection of chromoluminance patterns on chromoluminance pedestals I: threshold measurements.

Measurement of the detection thresholds of patterns on pedestals of various kinds has the potential of providing insight into the mechanisms that mediate pattern vision. This study is concerned with chromoluminance patterns, that is, patterns that vary over space in luminance, chromaticity, or both. Contrast thresholds for 1 c/deg Gabor patterns (targets) were measured as a function of the contrast of Gabor pedestal patterns (TvC functions), where the pedestals paired with each target were modulated in a wide range of directions in color space. For most target-pedestal pairs, the TvC function decreased (facilitation) and then increased as pedestal contrast increased. The increase went above the absolute contrast threshold (masking) for all target-pedestal pairs except in cases where facilitation occurred at the upper end of the pedestal contrast range. The specific form of the TvC function varied greatly with the target and pedestal, consistent with a general model of pedestal effects proposed by Foley [Journal of the Optical Society of America A, 1994, 11(6)]. There were two sets of target-pedestal pairs for which facilitation did not occur, but masking did occur: pairs in which the target was a luminance modulation and the pedestals were individually isoluminant and pairs in which the pedestal was blue/yellow and the target was in any of our directions except blue/yellow.

Adult↗
PubMed2000

Detection of chromoluminance patterns on chromoluminance pedestals II: model.

A model for chromoluminance pattern detection and pedestal effects is described. This model has five stages. The stimulus is first processed by the cone array and then by color-spatial linear operators. The outputs of the linear operators may be expressed as weighted sums of cone contrasts over space. There are three opposite sign pairs of linear spatial operators in the model. Their spectral tuning at each point in space is similar to the luminance, green/red and blue/yellow mechanisms in color opponent models, but their sensitivity to cone inputs varies as a function of space. The operators in each pair are the same except that the signs of the cone inputs in one are the opposite of those in the other. A non-linear response operator follows each linear operator. It receives two inputs, one excitatory and the other divisive inhibitory. The excitatory input is the half-wave rectified output of one of the linear operators. The inhibitory input is a non-linear sum of all linear operator outputs. The non-linear response operator raises the excitatory input to a power, and divides it by the inhibitory input plus a constant to produce the response. The detection variable is computed by combining the difference in response to target-plus-pedestal and pedestal alone across the three non-linear operators. The model accounts well for the large data set presented in the companion paper and is generally consistent with other results in the literature. The spectral sensitivities of the inferred chromoluminance pattern mechanisms are similar to those obtained with different methods. The data set is shown to be inconsistent with several other models.

Color Perception↗
PubMed2000

Circulating adhesion molecules and neutral endopeptidase enzymuria in patients with urolithiasis and hydronephrosis.

OBJECTIVES: To measure the concentrations of adhesion molecules (intercellular adhesion molecule-1 ¿ICAM-1, E-selectin, and L-selectin) in the serum of patients with renal stones and patients with hydronephrosis caused by obstructive ureteral stones. Renal tubular enzymes were examined from their urine samples to evaluate whether neutral endopeptidase (NEP) behaved as traditional tubular enzyme markers (N-acetyl-beta-glucosaminidase ¿NAG and beta-galactosidase ¿beta-GAL) in their disease state. METHODS: Three groups were studied. Group 1 included 15 normal volunteers, group 2 included 12 patients with ureteral stones and ipsilateral hydronephrosis, and group 3 included 17 patients with renal stones in one kidney without hydronephrosis or hydrocalycosis. A single, overnight fasting blood and urine sample was collected from each subject. Serum levels of ICAM-1, E-selectin, and L-selectin were measured by enzyme-linked immunosorbent assay. NEP, NAG, and beta-GAL were measured from urine samples, and the enzyme activities were expressed per gram of creatinine. RESULTS: Serum levels of ICAM-1 were higher in groups 2 and 3 (522 +/- 95 and 329 +/- 42 ng/mL, respectively), but the differences were only significant between group 2 and group 1 (263 +/- 32 ng/mL) and group 2 and group 3 (P <0.05). Serum levels of L-selectin were lower in group 3 and were significantly different when compared with groups 1 and 2 (P <0. 05). The serum levels of E-selectin were not significantly different among these three groups. Urinary levels of NEP were lower in group 2, although the levels of NAG and beta-GAL were more elevated than in group 1. CONCLUSIONS: Serum levels of ICAM-1 were elevated in patients with unilateral hydronephrosis caused by a ureteral stone, and E-selectin and L-selectin levels did not change significantly. These findings suggest that ICAM-1 may play a role in renal immune injury to ureteral obstruction. The urinary NEP values were lower in patients with hydronephrosis caused by ureteral stones, and the traditional lysosomal enzymes were increased. The lower urinary NEP values might suggest impairment of ipsilateral renal function. Renal stones per se resulted in no significant changes in serum adhesion molecule levels, although the levels of L-selectin were significantly decreased.

Cell Adhesion Molecules↗
PubMed2000

Synchronized release of dopamine and serotonin in the medial and lateral hypothalamus of rats.

A positive linear correlation between dopamine and serotonin release was found in the ventromedial hypothalamus and in the lateral hypothalamic area in fasting rats and in fed rats during intermeal intervals. Dopamine release in the ventromedial hypothalamus positively correlated with dopamine and serotonin release in the lateral hypothalamic area, which occurred only during intermeal intervals and was non-significant during the meal consumption periods or during fasting. Meal size correlated significantly only with a decrease in serotonin release in the lateral hypothalamic area. The study was designed to evaluate the relationship between dopamine and serotonin release in these hypothalamic areas and their dependence on feeding status. Microdialysis was performed simultaneously via two probes, one in the ventromedial hypothalamus and the other in the contralateral lateral hypothalamic area, of freely moving male lean Zucker rats over 24h with preserved light and dark phase, either with ad libitum access to food and water, or when no food was available. Dopamine and serotonin concentrations were measured by high-performance liquid chromatography with electrochemical detection in 20-min dialysis samples. Time-series analysis was applied to determine linear correlations between monoamines and in relation to food intake. Data showed that release of dopamine and serotonin is synchronized within the ventromedial hypothalamus and lateral hypothalamic area, particularly in the dark phase and when no food was ingested. However, synchronized release of monoamines between these nuclei occurred only during intermeal intervals: the periods of satiety. These findings suggest a tight relationship between dopaminergic and serotonergic systems of the lateral hypothalamic area and ventromedial hypothalamus, which is influenced by the feeding state and which may be involved in maintaining the balance within and between the centers of the parasympathetic and sympathetic nervous systems. The data also illustate that food intake is coupled unequivocally to the release of dopamine and serotonin in the hypothalamus, suggesting it as a mechanism of activation of postsynaptic neurons associated with new metabolic status.

Animals↗
PubMed2000

Local infusion of heparin reduces anastomotic neointimal hyperplasia in aortoiliac expanded polytetrafluoroethylene bypass grafts in baboons.

PURPOSE: Recently, we designed and characterized a novel expanded polytetrafluoroethylene (ePTFE)-based local drug delivery approach that selectively concentrates infused pharmacologic agents specifically within those blood layers adjacent to the graft wall and at downstream anastomotic sites. In this study, we locally administrated standard heparin therapy and evaluated its effects on neointimal hyperplasia formation in a baboon model of aortoiliac bypass graft placement. METHODS: Six adult male baboons underwent bilateral aortoiliac bypass grafting with ringed ePTFE (4 mm internal diameter x 5 cm length). In each animal, the distal anastomosis of one graft was continuously infused with heparin (50 U/h) and the distal anastomosis of the contralateral graft was infused with saline solution at the same rate (2.5 microL/h), with osmotic pumps implanted for 4 weeks. Platelet counts and activated partial thromboplastin time measurements were performed weekly. The specimens were harvested at 4 weeks and were subjected to morphometric analysis. Cell proliferation was assessed with bromodeoxyuridine immunostaining. RESULTS: All the harvested grafts were patent except for one control graft. There were no significant differences in platelet counts or activated partial thromboplastin time measurements taken before and during heparin infusion. As expected, there were no significant differences in graft neointimal hyperplasia and cell proliferation at the proximal anastomoses between the heparin-infused and control grafts. In contrast, at the treated distal anastomoses, heparin infusion significantly reduced the graft neointimal area by 65% and the cell proliferation index by 47% as compared with the untreated control distal anastomoses. CONCLUSION: These results show that local infusion of heparin significantly reduces distal anastomotic neointimal hyperplasia and cell proliferation without measurable systemic anticoagulation or other side effects. Thus, this approach may represent an attractive strategy for prolonging ePTFE bypass graft patency.

Anastomosis, Surgical↗
PubMed2000

Developmental remodeling of the retinogeniculate synapse.

Anatomical rearrangement of retinogeniculate connections contributes to the refinement of synaptic circuits in the developing visual system, but the underlying changes in synaptic function are unclear. Here, we study such changes in mouse brain slices. Each geniculate cell receives a surprisingly large number of retinal inputs (>20) well after eye-specific zones are formed. All but one to three of these inputs are eliminated over a 3-week period spanning eye opening. Remaining inputs are strengthened approximately 50-fold, in part through an increase in quantal size, but primarily through an increase in the number of release sites. Changes in release probability do not contribute significantly. Thus, a redistribution of release sites from many inputs to few inputs at this late developmental stage contributes to the precise receptive fields of thalamic relay neurons.

Aging↗
PubMed2000

Biological energy from the igneous rock enhances cell growth and enzyme activity.

Some effects from natural resources might be ignored and unused by humans. Environmental hormesis could be a phenomena necessary to bio-organism existence on earth. Since 1919, radiation and some heavy metal hormesis from the environment were proved in various reports. In this study, igneous rock with very low radioactivity and high ferrous activity was measured by multichannel analyzer and inductively coupled plasma analyzer. The water treated by igneous rock, both directly soaked or indirectly in contact, induced increased activities of glucose oxidase, catalase, peroxidase, and superoxide dismutase. It also increased cell growth of SC-M1, HCT-15, Raji, and fibroblast cell lines. The water after treatment of igneous rock had no change in pH values, but displayed decreased conductivity values. We assume that the igneous rock could transfer energy to water to change the molecular structure or conformation of water cluster, or by radiation hormesis effect could then induce increased enzyme activity and cell growth. It is also possible that the energy from rock may combine radiation hormesis with other transferable biological energy forms to change water cluster conformation.

Animals↗
PubMed2000

Evaluation of thrombolysis and angioplasty in a porcine iliac artery thrombosis model: application of endovascular stent-graft-induced thrombosis.

PURPOSE: To develop a novel endovascular thrombosis model in the porcine iliac artery for the evaluation of thrombolysis and angioplasty. MATERIALS AND METHODS: A stent-inversion-graft (SIG) model combining either a 3-mm or 5-mm tapered expandable polytetrafluoroethylene (ePTFE) graft attached within a self-expandable, 10-mm nitinol stent was placed in the left common iliac artery via an ipsilateral common femoral artery approach in 24 pigs. When the iliac artery was thrombosed, urokinase (250,000 IU) plus heparin (1,000 units) were pulse sprayed via a contralateral femoral approach (n = 12). Saline pulse-spray was used as a control group (n = 12). Balloon angioplasty was performed to eliminate the stenotic tapered graft within the stent after successful thrombolysis. The efficacy of the thrombolysis was assessed with use of intravascular ultrasound (IVUS) and arteriogram. RESULTS: Both the 3-mm tapered and 5-mm tapered SIG models caused iliac artery occlusion in 22 +/- 5 and 41 +/- 9 minutes, respectively, after the deployment. Luminal patency was re-established successfully in all occluded arteries after urokinase infusion. Angioplasty was successful in eliminating the tapered stenosis and restoring the normal diameter in all iliac arteries treated with urokinase. Complete thrombolysis was achieved in both models treated with urokinase. CONCLUSION: This novel endovascular approach of inducing arterial thrombosis is simple to perform and reliably produces arterial thrombosis. The intraluminal stenosis is also amenable to angioplasty. This model is useful for the evaluation of antithrombotic treatment modality and adjunctive endovascular interventions.

Alloys↗
PubMed2000

A simple physiologic pulsatile perfusion system for the study of intact vascular tissue.

Perfusion vascular culture models may provide a useful link between cell culture models and animal culture models by allowing a high level of control over important parameters while maintaining physiologic structure. The purpose of this study was to develop and test a new vascular culture system for pulsatile perfusion culture of intact vascular tissue. The system generates a pulsatile component of flow by means of a cam-driven syringe and a peristaltic pump and compliance chamber. Cams were designed, constructed and tested to simulate canine femoral and common carotid artery flows. The mean pressure was adjusted between 60 and 200 mmHg without significantly affecting flow rate, flow waveform, or the pressure waveform. Porcine common carotid artery segments were cultured in this pulsatile perfusion system. The viability of vascular segments was tested after various culture times with a functional assay that demonstrated both smooth muscle cell and endothelial cell response to vasomotor challenge.

Animals↗
PubMed2000

Probing the structure of monomers and dimers of the bacterial virus phi29 hexamer RNA complex by chemical modification.

All dsDNA viruses multiply their genome and assemble a procapsid, a protein shell devoid of DNA. The genome is subsequently inserted into the procapsid. The bacterial virus phi29 DNA translocating motor contains a hexameric RNA complex composed of six pRNAs. Recently, we found that pRNA dimers are building blocks of pRNA hexamers. Here, we report the structural probing of pRNA monomers and dimers by chemical modification under native conditions and in the presence or absence of Mg2+. The chemical-modification pattern of the monomer is compared to that of the dimer. The data strongly support the previous secondary-structure prediction of the pRNA concerning the single-stranded areas, including three loops and seven bulges. However, discrepancies between the modification patterns of two predicted helical regions suggest the presence of more complicated, higher-order structure in these areas. It was found that dimers were formed via hand-in-hand and head-to-head contact, as the interacting sequence of the right and left loops and all bases in the head loop were protected from chemical modification. Cryoatomic force microscopy revealed that the monomer displayed a check-mark shape and the dimer exhibited an elongated shape. The dimer was twice as long as the monomer. Direct observation of the shape and measurement of size and thickness of the images strongly support the conclusion from chemical modification concerning the head-to-head contact in dimer formation. Our results also suggest that the role for Mg2+ in pRNA folding is to generate a proper configuration for the right and head loops, which play key roles in this symmetrical head-to-head organization. This explains why Mg2+ plays a critical role in pRNA dimer formation, procapsid binding, and phi29 DNA packaging.

Bacillus Phages↗
PubMed2000

Green tea polyphenols react with 1,1-diphenyl-2-picrylhydrazyl free radicals in the bilayer of liposomes: direct evidence from electron spin resonance studies.

Free radical scavenging reactions of green tea polyphenols (GTP) were investigated with electron spin resonance (ESR) spectroscopy in the phospholipid bilayer of liposomes, using 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical as a model. The results showed that (1) GTP reacts with DPPH radicals in the bilayer of liposomes of both 1-hexadecanoyl-2-[(cis,cis,cis,cis,cis,cis)-4,7,10, 13,16,19-docosahexaenoyl]-sn-glycero-3-phosphocholine (DHAPC) and 1, 2-di[cis-9-hexadecenoyl]-sn-glycero-3-phosphocholine) (DPPC); and (2) GTP protects DHAPC liposomes effectively from the oxidation initiated by DPPH radicals. These results provide direct evidence that GTP reacts with free radicals in the model membrane and support the hypothesis that GTP protects unsaturated phospholipids from oxidation by reacting directly with the radicals.

Bepridil↗
PubMed2000

Isolation and characterization of two pathogen- and salicylic acid-induced genes encoding WRKY DNA-binding proteins from tobacco.

A pathogen- and salicylic acid (SA)-induced DNA-binding activity has been recently identified in tobacco that is related to a previously identified class of WRKY DNA-binding proteins. To identify members of the WRKY gene family associated with this DNA-binding activity, we have attempted to isolate those WRKY genes that are induced by pathogen infection. Using a domain-specific differential display procedure, we have isolated two tobacco WRKY genes, tWRKY3 and tWRKY4, that are rapidly induced in resistant tobacco plants after infection by tobacco mosaic virus (TMV). Both tWRK3 and tWRKY4 encode proteins with a single WRKY domain that contain the conserved WRKYGQK sequence. Unlike other isolated WRKY proteins that contain the Cys2His2 zinc motif, tWRKY3 and tWRKY4 appear to contain the Cys2HisCys zinc motif. Nonetheless, both tWRKY3 and tWRKY4 are capable of binding DNA molecules with the W-box (TTGAC) element recognized by other WRKY proteins. Expression of the tWRKY3 and tWRKY4 genes could be rapidly induced not only by TMV infection but also by SA or its biologically active analogues that are capable of inducing pathogenesis-related genes and enhanced resistance. Interestingly, induction of both genes by TMV infection was still observed in resistant tobacco plants expressing the bacterial salicylate hydroxylase gene (nahG), although the levels of induction appeared to be reduced. Identification of pathogen- and SA-induced genes encoding WRKY DNA-binding proteins should facilitate future studies on the regulation and functions of this novel group of DNA-binding proteins.

Amino Acid Sequence↗
PubMed2000

Importance of Dialister pneumosintes in human periodontitis.

Anaerobic bacteria play important roles in the pathogenesis of human periodontitis. This study examined the relationship between a potentially new periodontopathic bacterium Dialister pneumosintes and periodontal disease. A total of 73 women and 62 men aged 18 to 86 years participated in the study. Using a 16S rRNA polymerase chain reaction identification method, the presence of D. pneumosintes was determined in paper-point samples from periodontal pockets of 105 periodontitis and 30 gingivitis patients. D. pneumosintes was detected in 83% of patients having severe periodontitis and in 19% of patients having slight periodontitis. We suggest adding D. pneumosintes to the group of suspected periodontal pathogens.

Adolescent↗
PubMed2000

Frequency of 530-bp deletion in Actinobacillus actinomycetemcomitans leukotoxin promoter region.

Actinobacillus actinomycetemcomitans strains showing a 530-bp deletion in the promoter region of the leukotoxin gene operon elaborate high amounts of leukotoxin that may play a role in the pathogenesis of periodontal disease. This study used polymerase chain reaction detection to determine the occurrence of the 530-bp deletion in 94 A. actinomycetemcomitans strains from individuals of various ethnic backgrounds. Eleven blacks and one Hispanic subject but no Caucasian or Asian subjects showed the 530-bp deletion in the leukotoxin promoter region, suggesting that the deletion is mainly a characteristic of individuals of African descent. A. actinomycetemcomitans strains exhibiting a deletion in the leukotoxin promoter region occurred both in individuals having severe periodontitis and in adolescents revealing no evidence of destructive periodontal disease.

Actinobacillus Infections↗
PubMed2000

Family, peer, and individual correlates of depressive symptomatology among U.S. and Chinese adolescents.

This study examined the correlates of symptoms of depressed mood among adolescents in 2 dramatically different cultures (n = 502 in Tianjin, People's Republic of China; n = 201 in greater Los Angeles). Gender, stressful life events, perceived parental warmth, and conflict with parents were associated in the expected direction with depressive symptoms in each cultural setting. As predicted, regression analyses showed that the quality of family relationships and grades in school had significantly stronger associations with depressive symptoms among Chinese youths than among U.S. youths, whereas gender differences in depressive symptoms were greater among the U.S. youths. Peer warmth moderated the effects of particular risk factors for depressive symptoms in each cultural setting.

Adolescent↗