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Biomedical subjects

Jun Wang

Publications and source records attributed to Jun Wang.

At least 379 records · Page 21Linked to original sources
PubMed2004

Effects of four chlorobenzenes on serum sex steroids and hepatic microsome enzyme activities in crucian carp, Carassius auratus.

Four chlorobenzenes (chlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, p-chloro-methylbenzene) were administrated to the crucian carps (Carassius auratus) by peritoneal injections in the laboratory for 30 days. Serum testosterone and 17 beta-estradiol concentrations were detected using radioimmunology assay (RIA), and the activities of two hepatic microsome enzymes, glutathione s-transferase (GST) and UDP-glucuronosyltransferase (UDPGT), were measured using the modified methods as described by Habig and Owens. Results showed that the four chlorobenzenes caused significant increases in serum testosterone concentration in the crucian carps (P < 0.05) compared to the controls, but they caused no significant effect on 17 beta-estradiol level. All test chemicals caused a change in hepatic GST activity in crucian carps, with significant increases in enzyme activity (P < 0.05). Chlorobenzene, 1,3-dichlorobenzene and p-chloro-methylbenzene resulted in a marked inhibition to UDPGT activity in crucian carp (P < 0.05) except 1,4-dichlorobenzene. The changes in hepatic microsome enzyme activities may have resulted in the alterations of serum sex steroids levels in the crucian carps. The results indicated that these four chlorobenzenes may result in the changes of endocrine functions and may affect the reproductive success of this and other species.

Animals↗
PubMed2004

Quantitation of Taura syndrome virus by real-time RT-PCR with a TaqMan assay.

A real-time RT-PCR assay was developed using a TaqMan probe to detect and quantify Taura syndrome virus (TSV) in penaeid shrimp. A pair of RT-PCR primers, which amplify a 72 bp DNA fragment, and a TaqMan probe were selected from open reading frame 1 (ORF1) of the TSV genome. The primers and TaqMan probe used in this assay reacted with TSV isolates from Hawaii, Texas, Colombia, Mexico, Belize, Indonesia, and Thailand, but neither with RNA of healthy shrimp nor with an isolate of yellow head virus. A plasmid (pTSV-1) that contains the target TSV sequence was constructed and used to generate positive control RNA through in vitro transcription. The positive control RNA was used to demonstrate that the real-time RT-PCR assay has a detection limit of 100 copies and a log-linear range up to 10(8) copies of TSV RNA. This quantitative method was found to be highly reproducible, with low intra- and inter-assay variation. Coefficient of variation (CVs) values were 0.04-8.9 and 0.05-3.7%, respectively, for replicates within and among assays. This assay was used to quantify TSV in both acutely and chronically infected shrimp in a laboratory experiment. The quantities of TSV in the tissues of pleopods and gills were not significantly different, and there was no difference in TSV levels between the acutely and chronically infected groups. However, in the chronically infected shrimp, the quantities of TSV were one to two orders of magnitude higher in the lymphoid organ than in either gills or pleopods. This assay proved to be specific with high sensitivity, and it can be used to detect and quantify TSV in shrimp samples.

Animals↗
PubMed2004

Conserved "PAL" sequence in presenilins is essential for gamma-secretase activity, but not required for formation or stabilization of gamma-secretase complexes.

Generation of A beta from the beta-amyloid precursor protein (APP) requires a series of proteolytic processes, including an intramembranous cleavage catalyzed by an aspartyl protease, gamma-secretase. Two aspartates in presenilins (PS) are required for gamma-secretase activity (D257 and D385 of PS1), suggesting that PS may be part of this protease. Little is known concerning the importance of other sequences in PS for activity. We introduced point mutations (P433L, A434D, L435R) into a completely conserved region C-terminal to transmembrane domain eight of PS1. The P433L mutation abolished PS1 endoproteolysis as well as gamma-secretase cleavage of APP and Notch in PS1/2 K/O cells. In HEK cells, expression of PS1/P433L reduced A beta production and caused accumulation of APP C-terminal stubs. When the P433L mutation was introduced into the non-cleavable Delta exon 9 (Delta E9) variant of PS1, it abolished gamma-secretase cleavage of APP and Notch. The P433L holoprotein is stable and incorporated into the high molecular weight gamma-secretase complex, arguing that P433 is not necessary for formation or stabilization of the gamma-secretase complex. Other non-conservative mutations in the invariant P(433)A(434)L(435) sequence also result in a phenotype that is indistinguishable from the aspartate mutants, suggesting a direct involvement of this sequence in gamma-secretase activity.

Amino Acid Sequence↗
PubMed2004

Mutations in APP have independent effects on Abeta and CTFgamma generation.

Understanding the molecular mechanism of beta-amyloid (Abeta) generation is crucial for Alzheimer's disease pathogenesis as well as for normal APP function. The transmembrane domain (TM) of APP appears to undergo presenilin-dependent gamma-secretase cleavage at two topologically distinct sites: a site in the middle of the TM domain that is crucial for the generation of Abeta-peptides, and a site close to the cytoplasmic border (S3-like/epsilon site) of the TM domain that leads to production of the APP intracellular domain (CTFgamma/AICD). We demonstrate that, in contrast to the unique effect of familial Alzheimer's disease (FAD) mutations in APP on Abeta42 production, some but not all FAD mutations also affect CTFgamma generation. Furthermore, changes in total CTFgamma levels do not correlate with either an increase or a decrease of any Abeta species, and inhibition of Abeta-peptide formation starting from position +1 (Abeta1-x) does not affect CTFgamma production. These results suggest that cleavage at the gamma40/42- and the S3-like sites can be dissociated, and that APP signaling and Abeta production are not tightly linked.

Alzheimer Disease↗
PubMed2004

Absolute exponential stability of recurrent neural networks with Lipschitz-continuous activation functions and time delays.

This paper investigates the absolute exponential stability of a general class of delayed neural networks, which require the activation functions to be partially Lipschitz continuous and monotone nondecreasing only, but not necessarily differentiable or bounded. Three new sufficient conditions are derived to ascertain whether or not the equilibrium points of the delayed neural networks with additively diagonally stable interconnection matrices are absolutely exponentially stable by using delay Halanay-type inequality and Lyapunov function. The stability criteria are also suitable for delayed optimization neural networks and delayed cellular neural networks whose activation functions are often nondifferentiable or unbounded. The results herein answer a question: if a neural network without any delay is absolutely exponentially stable, then under what additional conditions, the neural networks with delay is also absolutely exponentially stable.

Algorithms↗
PubMed2004

A recurrent neural network with exponential convergence for solving convex quadratic program and related linear piecewise equations.

This paper presents a recurrent neural network for solving strict convex quadratic programming problems and related linear piecewise equations. Compared with the existing neural networks for quadratic program, the proposed neural network has a one-layer structure with a low model complexity. Moreover, the proposed neural network is shown to have a finite-time convergence and exponential convergence. Illustrative examples further show the good performance of the proposed neural network in real-time applications.

Artificial Intelligence↗
PubMed2004

Regulation of cell-cell adhesion during Dictyostelium development.

During development of Dictyostelium, four adhesion systems have been identified and adherens junction-like structures have been discovered in the fruiting body. The temporal and spatial expression of cell adhesion molecules (CAMs) is under stringent developmental control, corresponding to major shifts in morphological complexity. Genetic manipulations, including over-expression and knockout mutations, of the adhesion genes, cadA (encoding DdCAD-1), csaA (gp80) and lagC (gp150), have shed light on new roles for cell adhesion molecules in aggregate size regulation, cell-type proportioning, cell differentiation and cell sorting. As cell-cell interactions remain highly dynamic within cell streams and aggregates, mechanisms must exist to facilitate the rapid assembly and disassembly of adhesion complexes. Studies on gp80 have led to a model for the rapid assembly of adhesion complexes via lipid rafts.

Animals↗
PubMed2004

Utilization of nitrite as a nitrogen source by Botryococcus braunii.

Nitrite at 2 mM did not affect the growth of Botryococcus braunii and served as the sole nitrogen source giving a minimum biomass doubling time of 4.2 d, which was equal to that of the culture using 4 mM nitrate as nitrogen source. With nitrite at 4 mM, after a lag phase of about 10 d, the alga grew quickly, reaching 1.1 g l(-1) at the end. Respective nitrite removals were 100% and 99.7%. There were few differences in the hydrocarbons produced using different nitrogen sources.

Bioreactors↗
PubMed2004

Enzymatic characterization and functional groups of polyphenol oxidase from the pupae of blowfly (Sarcophaga bullata).

Polyphenol oxidase (EC 1.14.18.1) was purified from the pupae of blowfly (Sarcophaga bullata) by a procedure involving ammonium sulfate fractionation and chromatography on DEAE-cellulose and Sephadex G-100. Kinetic characteristics of the enzyme were determined using L-DOPA as substrate. The specific activity of the enzyme was 770 U/mg, and the Michaelis constant (Km) was 1.5 +/- 0.1 mM (pH 6.8, 30 degrees C). Activity was maximal at 40 degrees C, pH 6.5. Chemical modification experiments demonstrated that cysteine and tryptophan residues are essential and arginine residues are not essential to the enzyme function. The enzyme is inhibited by quercetin with an IC50 of 0.20 +/- 0.06 mM. The inhibition is of competitive type, and the inhibition constant was determined to be 88 micro M.

Animals↗
PubMed2004

Apoptotic and antiapoptotic effects of CXCR4: is it a matter of intrinsic efficacy? Implications for HIV neuropathogenesis.

CXCR4, the specific receptor for the chemokine SDF-1 alpha that also binds CXCR4-using HIV gp120s, affects survival of different cell types, including neurons. However, current data show that the outcome of CXCR4 activation on neuronal survival may vary depending on the ligand and/or the cellular conditions. In this study, we have systematically compared the effects of SDF-1 alpha and gp120(IIIB) (with or without CD4) on several intracellular pathways involved in cell survival, including MAP kinases and Akt-dependent pathways. Our data show that gp120(IIIB) and SDF-1 alpha are both potent activators of MAP kinases in neuronal and non-neuronal cells, though the kinetic of these responses is slightly different. Furthermore, unlike SDF-1 alpha, and independently of CD4, gp120(IIIB) is unable to stimulate Akt and some of its antiapoptotic targets (NF-kappa B and MDM2)--despite its ability to activate other signaling pathways in the same conditions. Finally, the viral protein is more efficient in recruiting some effectors (e.g., JNK) than others in comparison with SDF-1 alpha (EC(50) = 0.1 vs. 0.6 nM). We conclude that the intrinsic efficacy of the two ligands is significantly different and is pathway dependent. These findings have important implications for our understanding of CXCR4-mediated responses in the CNS, as well as the role of this coreceptor in HIV neuropathogenesis.

Animals↗
PubMed2004

Anaplastic large cell lymphoma associated with Epstein-Barr virus following cardiac transplant.

Posttransplantation lymphoproliferative disorders (PTLDs) eventually occur in approximately 5% of all organ transplant recipients. Most of cases are B-cell proliferations associated with the Epstein-Barr virus (EBV). T-cell PTLDs are relatively rare, although some estimate that up to 14% of posttransplantation malignant lymphomas are T-cell lymphomas even though only a few of these cases are described in the literature. A literature review found only 77 cases of T-cell PTLD, including 1 case following cardiac transplant, 15 cases associated with EBV, and only 1 case of anaplastic large cell lymphoma (ALCL). This single ALCL case followed a liver transplant, was of the T-cell phenotype, and was EBV negative. In this report, we describe a 14-year-old male who developed an EBV-positive, T-cell PTLD of the ALCL subtype after a period of 14 years following cardiac transplant. Immunohistochemical staining established the T-cell origin of the neoplasm with strong expression of CD45, CD3, CD43, and CD2 and also showed expression of CD30 consistent with the histologic features that suggested ALCL. EBER in situ hybridization detected the presence of the EBV. Polymerase chain reaction analysis for T-cell receptor-gamma gene rearrangements confirmed the T-cell lineage of this lymphoma. To our knowledge, this is the first reported case of an EBV-positive T cell lymphoma of the anaplastic large cell subtype following organ transplant.

Adolescent↗
PubMed2004

Small physiologic changes in calcium and magnesium alter excitability and burst firing of CA1 pyramidal cells in rat hippocampal slices.

The effects of small physiologic changes in Ca and Mg concentrations on neuronal burst firing were examined. Intracellular electrophysiologic recordings were made from CA1 pyramidal neurons in rat hippocampal slices. There was no difference in the resting potential or the input resistance of neurons bathed in the lower Ca-Mg artificial Cerebrospinal fluid (aCSF) (1.4 mM Ca; 1.3 mM Mg) compared with the higher Ca-Mg aCSF (2 mM Ca; 2 mM Mg). However, neurons in the lower Ca-Mg aCSF, but not the higher Ca-Mg aCSF, demonstrated depolarizing waves and bursts of action potentials; no single component of the aCSF accounted for this difference. Reducing the Ca from 2 to 1 mM in the higher Ca-Mg aCSF increased the mean frequency of action potentials from 28 to 171 Hz; the addition of 6-cyano-7-nitroquinoxaline-2,3-dione did not reduce the frequency. The threshold of potassium for inducing bursts was 5.25 with 1 mM Ca, 7.25 with 2 mM Ca, and 11.25 with 3 mM Ca. When Mg was reduced from 2 to 1 mM, the number of potassium-induced bursts increased to 190%; increasing Mg from 2 to 3 mM reduced the bursts to 58% (frequency with 2 mM Mg set to 100%). Small decreases in extracellular Ca and/or Mg led to increased excitability and burst firing, which may alter physiologic and pathophysiologic processes such as enhancing long-term potentiation, pain transmission, epileptogenesis, and neuronal damage and decreasing anesthetic potency. Increases in extracellular Ca and/or Mg would have the opposite effect on these processes. These effects of extracellular divalent ions on burst firing may explain some of the pathophysiologic effects of hypocalcemia and hypomagnesemia.

Action Potentials↗
PubMed2004

A general projection neural network for solving monotone variational inequalities and related optimization problems.

Recently, a projection neural network for solving monotone variational inequalities and constrained optimization problems was developed. In this paper, we propose a general projection neural network for solving a wider class of variational inequalities and related optimization problems. In addition to its simple structure and low complexity, the proposed neural network includes existing neural networks for optimization, such as the projection neural network, the primal-dual neural network, and the dual neural network, as special cases. Under various mild conditions, the proposed general projection neural network is shown to be globally convergent, globally asymptotically stable, and globally exponentially stable. Furthermore, several improved stability criteria on two special cases of the general projection neural network are obtained under weaker conditions. Simulation results demonstrate the effectiveness and characteristics of the proposed neural network.

Neural Networks, Computer↗
PubMed2004

Incremental learning with balanced update on receptive fields for multi-sensor data fusion.

This paper addresses multi-sensor data fusion with incremental learning ability. A new cost function is proposed for the receptive field weighted regression (RFWR) algorithm based on the idea of back propagation (BP), so that the computation efficiency and the learning strategy of the modified RFWR are much more applicable for multi-sensor data fusion problem. Thus a new fusion structure and algorithm with incremental learning ability is constructed by adopting the modified RFWR algorithm together with the weighted average algorithm. Experiments of a two-camera unified positioning system are implemented successfully to test the proposed computation structure and algorithms.

Journal Article↗
PubMed2004

Obstacle avoidance for kinematically redundant manipulators using a dual neural network.

One important issue in the motion planning and control of kinematically redundant manipulators is the obstacle avoidance. In this paper, a recurrent neural network is developed and applied for kinematic control of redundant manipulators with obstacle avoidance capability. An improved problem formulation is proposed in the sense that the collision-avoidance requirement is represented by dynamically-updated inequality constraints. In addition, physical constraints such as joint physical limits are also incorporated directly into the formulation. Based on the improved problem formulation, a dual neural network is developed for the online solution to collision-free inverse kinematics problem. The neural network is simulated for motion control of the PA10 robot arm in the presence of point and window-shaped obstacle.

Journal Article↗
PubMed2004

A one-layer recurrent neural network for support vector machine learning.

This paper presents a one-layer recurrent neural network for support vector machine (SVM) learning in pattern classification and regression. The SVM learning problem is first converted into an equivalent formulation, and then a one-layer recurrent neural network for SVM learning is proposed. The proposed neural network is guaranteed to obtain the optimal solution of support vector classification and regression. Compared with the existing two-layer neural network for the SVM classification, the proposed neural network has a low complexity for implementation. Moreover, the proposed neural network can converge exponentially to the optimal solution of SVM learning. The rate of the exponential convergence can be made arbitrarily high by simply turning up a scaling parameter. Simulation examples based on benchmark problems are discussed to show the good performance of the proposed neural network for SVM learning.

Journal Article↗
PubMed2004

Constrained motion control of flexible robot manipulators based on recurrent neural networks.

In this paper, a neural network approach is presented for the motion control of constrained flexible manipulators, where both the contact force everted by the flexible manipulator and the position of the end-effector contacting with a surface are controlled. The dynamic equations for vibration of flexible link and constrained force are derived. The developed control, scheme can adaptively estimate the underlying dynamics of the manipulator using recurrent neural networks (RNNs). Based on the error dynamics of a feedback controller, a learning rule for updating the connection weights of the adaptive RNN model is obtained. Local stability properties of the control system are discussed. Simulation results are elaborated on for both position and force trajectory tracking tasks in the presence of varying parameters and unknown dynamics, which show that the designed controller performs remarkably well.

Algorithms↗