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Biomedical subjects

J Shen

Publications and source records attributed to J Shen.

At least 289 records · Page 16Linked to original sources
PubMed1998

Modelling inter-ward migration in Hereford and Worcester: the importance of housing growth and tenure.

"In this paper, we use the 1991 Special Migration Statistics to analyse inter-ward flows in the British county of Hereford and Worcester. New modelling techniques...based on the Poisson distribution are used in this research which partially overcome the under-dispersion problem resulting from modelling zero and very small flows.... Analysis at this scale provides the potential for more detailed generalization about migration processes such as suburbanization, counterurbanization, intra-urban mobility, rural depopulation and the relationship between housing and demographic change at the local level. Unlike migration flows over long distances, which are often employment related, these flows are primarily motivated by residential requirements and housing type and growth are identified as key variables in the interpretation of these migration patterns."

Demography↗
PubMed1998

Filter-based coded-excitation system for high-speed ultrasonic imaging.

We have recently presented a new algorithm for high-speed parallel processing of ultrasound pulse-echo data for real-time three-dimensional (3-D) imaging. The approach utilizes a discretized linear model of the echo data received from the region of interest (ROI) using a conventional beam former. The transmitter array elements are fed with binary codes designed to produce distinct impulse responses from different directions in ROI. Image reconstruction in ROI is achieved with a regularized pseudoinverse operator derived from the linear receive signal model. The reconstruction operator can be implemented using a transversal filter bank with every filter in the bank designed to extract echoes from a specific direction in the ROI. The number of filters in the bank determines the number of image lines acquired simultaneously. In this paper, we present images of a cyst phantom reconstructed based on our formulation. A number of issues of practical significance in image reconstruction are addressed. Specifically, an augmented model is introduced to account for imperfect blocking of echoes from outside the ROI. We have also introduced a column-weighting algorithm for minimizing the number of filter coefficients. In addition, a detailed illustration of a full image reconstruction using subimage acquisition and compounding is given. Experimental results have shown that the new approach is valid for phased-array pulse-echo imaging of speckle-generating phantoms typically used in characterizing medical imaging systems. Such coded-excitation-based image reconstruction from speckle-generating phantoms, to the best of our knowledge, have not been reported previously.

Artifacts↗
PubMed1998

A flow cytometric method for rapid selection of novel industrial yeast hybrids.

We rapidly produced and isolated novel yeast hybrids by using two-color flow cytometric cell sorting. We labeled one parent strain with a fluorescent green stain and the other parent with a fluorescent orange stain, and hybrids were selected based on their dual orange and green fluorescence. When this technique was applied to the production of hybrids by traditional mating procedures, more than 96% of the isolates were hybrids. When it was applied to rare mating, three hybrids were identified among 50 isolates enriched from a population containing 2 x 10(6) cells. This technology is not dependent on genetic markers and has applications in the development of improved industrial yeast strains.

Flow Cytometry↗
PubMed1998

Functional energy metabolism: in vivo 13C-NMR spectroscopy evidence for coupling of cerebral glucose consumption and glutamatergic neuronalactivity.

The use of in vivo 13C nuclear magnetic resonance spectroscopy (NMR) has established the pathways of functional interaction between neurons and astrocytes in the mammalian brain and enabled quantitation of these fluxes. A mathematical model of glutamate, glutamine and ammonia metabolism in the brain has been developed, under the constraints of carbon and nitrogen mass balance, allowing the direct and quantitative comparison of in vivo 13C- and 15N-NMR data. Using this model and 13C-NMR data, the authors have separated the neurotransmitter cycling and detoxification components of glutamine synthesis by measuring the rate of glutamine synthesis under normal and hyperammonaemic conditions in the rat brain cortex in vivo. In addition, the simultaneous measurement of the rates of oxidative glucose metabolism and glutamate neurotransmitter cycling in the rat brain cortex has shown that over a range of EEG activity (from isoelectric up to near-resting levels) the stoichiometry between glucose metabolism and glutamate cycling is close to 1:1. Under mild anesthesia, cortical glucose oxidation coupled to glutamatergic synaptic activity accounts for over 80% of total glucose oxidation. Previously, changes in cerebral glucose metabolism have been taken to indicate alterations in functional activity. These recent in vivo results demonstrate, however, that those changes are, in fact, quantitatively coupled to the crux of functional activity, neurotransmitter release. These findings bear upon a number of hypotheses concerning the neurophysiological basis of brain functional imaging methods.

Animals↗
PubMed1998

15N-NMR spectroscopy studies of ammonia transport and glutamine synthesis in the hyperammonemic rat brain.

Ammonia transport and glutamine synthesis were studied in the hyperammonaemic rat brain in vivo using 15N-NMR spectroscopy at a plasma ammonia level of approximately 0.39 mM raised via an intravenous [15N]-ammonium acetate infusion. The initial slope of the time course of the summed cerebral 15N-labelled metabolites was used to determine the rate of ammonia net transport during hyperammonemia as 0.13 +/- 0.02 micromol/min/g (mean +/- SD; n = 5). Based on the total accumulation of glutamine and the 1:2 stoichiometric relationship between fluxes of four-carbon skeletons and nitrogen atoms, the rate of de novo glutamine synthesis through anaplerosis and subsequent glutamate dehydrogenase action was calculated to be 0.065 +/- 0.01 micromol/min/g. The rate of total glutamine synthesis was estimated to be 0.20 +/- 0.06 micromol/min/g (n = 5) by fitting the [5-15N]glutamine time course to a previously described model of glutamate-glutamine cycling between astrocytes and neurones. A large dilution was also observed in [2-15N]glutamine, which supports the glutamate-glutamine cycle as being an important pathway for neuronal glutamate repletion in vivo.

Acetates↗
PubMed1998

[A study on the relationship between Lp(a) and arteriosclerotic cerebral infarction].

Using a 1:1 matched case control study, we analysed the data of 105 arteriosclerotic cerebral infarction cases and controls to detect the levels of TC, TG, HDL-C, LDL-C and Lp(a). The results showed that the average level of Lp(a) in cases was (238.38 mg/L), significantly higher than that of controls (149.98 mg/L t = 3.96, P < 0.001). Comparing the levels of different age groups and sex, no significant difference, except the group over 70 years, which was higher than that in other groups was found. Dose-response analysis also showed that the OR value was positively correlated with the Lp(a). Multi-variable logistic regression model indicated that Lp(a) was an independent risk factor with OR = 1.93. Another risk factor was TG. However, LDL-C, HDL-C were found to be the protective factors of arteriosclerotic cerebral infarction, with an OR = 0.32.

Aged↗
PubMed1998

[Calculating method for the necessary lamps and sterile rate in a tube-shaped ultraviolet air washer].

It has much more advantage to use the cylindric ultraviolet air washer than to use the ordinary ultraviolet lamps. There was a calculation method for determining necessary lamps in a rectangled ultraviolet air washer, but it had a limiting condition. This paper developed two calculating methods for determining necessary lamps and its sterile rate in a tube-shaped ultraviolet air washer. The sterile rate can be extracted with any parameter. Necessary lamps can also be extracted with its sterile rate.

Air Microbiology↗
PubMed1998

[Effects of no and endothelium on carotid baroreceptor activity].

The present study was undertaken to examine the effects of endothelium and exogenous NO on the baroreceptor discharge of the carotid sinus. The baroreceptor activity (BRA) was recorded from the rabbit carotid sinus-sinus nerve (CS-CSN) preparation using a chamber for superfusing and perfusing the tissue. The results are as follows. (1) The CSN basal discharge could be divided into two components, a low-amplitude component and a high-amplitude one. The high-amplitude discharge was dependent on pulsatory perfusing pressure, but did not respond to classical chemoreceptor stimulants, indicating its baroreceptive origin. (2) The BRA was decreased after removal of the endothelium. (3) L-arginine (L-arg), as exogenous NO, initiated BRA in a dose-dependent manner, which was prevented by precedent inhibition of NO synthase or by removal of the endothelium. (4) Inhibition of guanine nucleotide cyclase with methylene blue affected neither the basal BRA nor the response of BRA to L-arg. These results indicate that stimulation of BRA by exogenous NO may be mediated by the endothelium, but cGMP dose not seem to be involved.

Animals↗
PubMed1998

[90Y glass microspheres intraradiopraxis of advanced hepatic carcinoma].

OBJECTIVE: To evaluate intraradiopraxis with (90)Y glass microspheres for advanced hepatic carcinoma. METHOD: 28 patients were divided into two group: A treated by (90)Y and hepatic artery embolism and chemotherapy (HAEC) (n = 13), and B by (90)Y and hepatic artery embolism (HAE) (n = 15), and 15 cases (group C) only treated by HACE simultaneously were used as controls. The average age, course, and diameter of tumor were similar in all groups (P > 0.05). RESULT: The effective rate of the group A and B was 61.5% and 66.6% respectively, and that of the group C was only 33.3% (P < 0.001). The average survival time of the group A and B was 9.86 and 11.9 months respectively, and that of the group C was only 4.5 months (P < 0.001). CONCLUSION: The intraradiopraxis with (90)Y glass microsphere would be a valuable method for patients with hypo-leukocyte count, insensitive to chemotherapy or resistant to chemotherapy.

Adult↗
PubMed1998

[Studies on chemical constituents of Tinospora hainanesis].

Tinospora hainanesis is a new species of Menispermaceae plant. It is used as folk remedy for joint pain and physical injury. Five compounds were isolated from the vine stalk of Tinospora hainanesis. By spectral analysis and chemical methods, the structures of the compounds were identified as makisterone A (I), 2,3-dimethoxy-9,10-dihydroxy-N-methyltetrahydroproto-berberine quaternary salt (II), palmatine (III), beta-amyrin (IV) and docosyl ferulate (V). II is a new quaternary alkaloid named as haitinosporine. I, IV and V were isolated for the first time from the plants of Tinospora genus.

Berberine Alkaloids↗
PubMed1998

Androgen regulation of the human pseudoautosomal gene MIC2, a potential marker for prostate cancer.

Using the differential display-polymerase chain reaction technique to identify androgen-responsive genes in the human prostatic tumor cell line LNCaP, we cloned an expression tag homologous to the human pseudoautosomal gene MIC2. The role of MIC2 in the prostate had not previously been studied. We used a series of cell lines derived from LNCaP that varied in their degree of differentiation and metastatic potential to assess the relationship between MIC2 expression and androgen responsiveness in prostate cancer. The expression of MIC2 mRNA and its product E2 was upregulated by androgen in a dose- and time-dependent manner in the parental LNCaP line and correlated with the expression of prostate-specific antigen. In the LNCaP sublines and an androgen-repressed invasive human prostate cancer cell line (ARCaP), MIC2 gene expression was not regulated by androgen and was associated with poorer differentiation, decreased androgen sensitivity, and higher metastatic potential. Immunohistochemical analyses indicated that E2 was expressed in tissues from patients with primary prostate cancer (16 of 20), in fetal prostatic tissues (low levels in all 10 fetal tissues assessed), and sporadically in benign prostatic hyperplasia tissues (one of four). The normal prostate tissues did not show positive E2 staining, with the exception of one central-zone section from one of the eight normal prostate samples assessed. These findings suggest that deregulation of expression of the human pseudoautosomal gene MIC2 occurred in the prostate.

12E7 Antigen↗
PubMed1997

Modification of humoral responses by the combination of leflunomide and cyclosporine in Lewis rats transplanted with hamster hearts.

BACKGROUND: Vigorous antibody-mediated responses prevent the successful engraftment of hamster hearts transplanted into Lewis rats. Early antibody responses mediating acute rejection of the xenograft are T cell-independent and resistant to the T-cell immunosuppressant, cyclosporine (CsA). Immunosuppression with the combination of leflunomide plus CsA completely prevents xenograft rejection, but when such immunosuppression is stopped the hamster heart is rejected by a process that we term late xenograft rejection. We report here on some of the immunological features of late xenograft rejection. METHODS: Lewis rats transplanted with hamster hearts were treated with leflunomide (5 mg/kg/day by gavage) for 14-21 days and CsA (20 mg/kg/day by gavage) continuously from the day of transplant. Serum was harvested and the functional activities of the xenoreactive antibodies were quantitated by in vivo passive transfer of sera, flow cytometry, in vitro C3 deposition assays, and Western blotting. RESULTS: CsA alone prevented late xenograft rejection and the accompanying production of xenoreactive antibodies. The xenoreactive antibodies accompanying acute or late xenograft rejection were predominantly IgM, but only serum from rats undergoing acute xenograft rejection was able to induce hyperacute rejection. The ability of serum to induce hyperacute rejection correlated with its ability to induce C3 deposition on hamster lymphocytes in vitro. The repertoire of hamster antigens recognized by IgM in the serum of rats undergoing late xenograft rejection is more restricted than that of IgM in the serum of rats undergoing acute xenograft rejection. We additionally demonstrate that long-term graft survival is not dependent on graft accommodation. CONCLUSIONS: These studies demonstrate that a brief treatment with the combination of leflunomide and CsA profoundly modifies the humoral xenoreactivity in the recipient, converting it from a T-independent into a T cell-dependent response. Differences in functional activity of sera from acute or late xenograft rejection suggest that antigenic specificity defines the ability of IgM to induce complement activation and hyperacute rejection.

Animals↗
PubMed1997

Does retrograde warm blood cardioplegia provide equal protection to both ventricles? A magnetic resonance spectroscopy study in pigs.

BACKGROUND: The degree of protection provided to the right ventricle during retrograde continuous normothermic blood cardioplegia (RCNBC) remains controversial. The purpose of this study was to determine whether RCNBC is able to provide "adequate" nutritive flow to both ventricles to prevent ischemic metabolism in normal swine hearts. Localized 31P magnetic resonance spectroscopy (MRS) was used to monitor the changes in energy metabolism and intracellular pH (pHi) in each ventricle separately. METHODS AND RESULTS: Isolated normal swine hearts received 20 minutes of antegrade continuous normothermic blood cardioplegia (ACNBC) for collection of control (baseline) data, followed by 20 minutes of RCNBC. This protocol was repeated four times in five hearts and twice in two hearts. Perfusion pressure was maintained between 70 to 85 and 38 to 43 mm Hg during ACNBC and RCNBC, respectively. pHi, creatine phosphate (PCr), inorganic phosphate (Pi), and ATP were measured continuously in each ventricle during ACNBC and RCNBC, using localized 31P MRS with two surface coils. RCNBC resulted in a significant increase in Pi (LV 222% and RV 244% of the baseline levels, respectively) and a decrease in PCr (left ventricle [LV] to 68% and right ventricle [RV] to 31% of the baseline levels, respectively) in both ventricles relative to ACNBC. The PCr level was significantly lower in the RV than in the LV (31% versus 68%, P<.001) during RCNBC. In one series of experiments (n=5) where ACNBC and RCNBC were alternated every 20 minutes (ACNBC, RCNBC, ACNBC, RCNBC, ACNBC) for a total of 100 minutes, Pi and PCr recovered completely. A continuous and significant decrease in ATP was observed in the RV, and no recovery of ATP was found when switching from RCNBC to ACNBC. No significant decrease in ATP was observed in the LV. pHi remained unchanged in both ventricles during alternate ACNBC and RCNBC. CONCLUSIONS: Energy metabolism in the RV is less well preserved than in the LV during RCNBC. A combination of ACNBC and RCNBC seems to provide good cardiac protection as measured by the recovery of cardiac energetics and pHi.

Adenosine Triphosphate↗
PubMed1997

The effect of in vivo ethanol consumption on cyclic AMP and delta-opioid receptors in mouse striatum.

In this study the effect of in vivo ethanol consumption on cyclic AMP (cAMP) and [D-Ala2,D-Leu5]enkephalin (DADLE) inhibition of forskolin-stimulated cAMP production was examined in mouse striatum. Effects of ethanol on striatal delta-opioid receptor (DOR) density and mRNA were also examined. Mice had unlimited access to 7% (v/v) ethanol alone or water for 1 or 7 days and were then sacrificed and striatum removed for analysis. There was no difference in basal cAMP formation between water and ethanol-treated mouse striatum following 7 day treatment, and a small, but statistically significant increase in basal cAMP in the ethanol group following 1 day treatment. Both 1 day and 7 day ethanol treatment did not significantly alter the percentage increase in cAMP following treatment with 10 microM forskolin. There was a significant effect of ethanol treatment on the maximum inhibitory effect of DADLE on forskolin-stimulated cAMP formation following both 1 and 7 day ethanol treatment. The DADLE IC50 was unaffected by ethanol treatment. Saturation binding studies ([3H]Deltorphin II) indicated no effect of ethanol on Bmax or Kd in striatum. Similarly, no difference between water and ethanol-treated was observed for DOR mRNA in striatum. These data indicate that ethanol consumption can alter opioid regulation of cAMP formation. However, this effect is not related to changes in any delta-opioid receptor parameters that were examined.

Animals↗
PubMed1997

The effect of aging on experience-dependent plasticity of hippocampal place cells.

The firing characteristics of 1437 CA1 pyramidal neurons were studied in relation to both spatial location and the phase of the theta rhythm in healthy young and old rats performing a simple spatial task on a rectangular track. The old rats had previously been found to be deficient on the Morris spatial learning task. Age effects on the theta rhythm per se were minimal. Theta amplitude and frequency during rapid eye movement sleep were virtually identical. During behavior, theta frequency was slightly reduced with age. In both groups, cell firing occurred at progressively earlier phases of the theta rhythm as the rat traversed the place field of the cell (i. e., there was "phase precession," as reported by others). The net phase shift did not differ between age groups. The main finding of the study was a loss of experience-dependent plasticity in the place fields of old rats. During the first lap around the track on each day, the initial sizes of the place fields were the same between ages; however, place fields of young rats, but not old, expanded significantly during the first few laps around the track in a given recording session. As the place fields expanded, the rate of change of firing with phase slowed accordingly, so that the net phase change remained constant. Thus changes in field size and phase precession are coupled. A deficit in plasticity of place fields in old rats may lead to a less accurate population code for spatial location.

Action Potentials↗
PubMed1997

A theoretical investigation of tight-binding thermolysin inhibitors.

A tight-binding thermolysin inhibitor, Cbz-Phe-psi[PO2NH]-Leu-Ala (ZFpLA, Ki = 0.068 nM), and its analogs, ZRp(O)LA (R = Ala, Leu or Phe) have been studied using the finite difference solution to the linearized Poisson-Boltzmann equation (FDPB) and solvation entropy correction (SEC). The binding energy difference between conformationally different thermolysin inhibitors ZFpLA and ZGpLL is estimated using three approaches. Two of approaches use the X-ray structures of ZFpLA-thermolysin and ZGpLL-thermolysin structures. The third one uses both X-ray structures to calculate binding energy differences from ZFpLA and ZGpLL to a hypothetical intermediate MepLA. All the results are qualitatively correct with one closely reproducing the experimental value. The enhancement of the ZFpLA binding is attributed largely to the solvation entropy or "hydrophobic force". The binding mode of the ZGpLR N-terminal moiety appears to be electrostatically unfavorable. Reducing the polarity of that moiety is predicted to enhance binding affinity. The binding trends due to the hydrophobic variation of ZRp(O)LA are calculated within 1 kcal/mol of the experimental values. Increasing lipophilicity of a ligand favors the binding due to the difference of surface area change between the free state and the bound state. The analysis of energetic components shows that these trends are not specific for the binding of phosphorus-containing inhibitors but are generally true for protein-ligand interactions. The electrostatic calculation does not support the involvement of the second protonation of ZFpLA in binding. Therefore, reexamining the second protonation of ZFpLA or seeking further experimental support seems appropriate. The structural sensitivity of the FDPB calculation was assessed by using ligand and receptor structures from different X-ray studies of thermolysin. The small deviations (< 0.3 A) in the receptor structures do not cause significant changes in electrostatic binding energy if there is no structural change in modified regions.

Binding Sites↗
PubMed1997

Quantitation of the changes in splenic architecture during the rejection of cardiac allografts or xenografts.

BACKGROUND: The spleen plays a central role in the generation of both cellular and antibody responses during graft rejection. Although changes in lymphocyte function have been extensively analyzed in vitro, there have been limited attempts at quantitating the structural changes in the lymphoid compartments within the spleen during graft rejection. METHODS: We describe here a means of quantitating the histological changes in the spleen using immunohistochemical techniques and computerized image analysis. RESULTS: Allograft rejection at 6 days after transplant is characterized by a threefold increase in the T cell-rich areas of the periarteriolar lymphoid sheaths (PALs). The follicular areas are enlarged and germinal centers appear in 55% of the white pulp regions. Acute xenograft rejection, 4 days after transplant, is specifically accompanied by a 2.3-fold increase in the marginal zone (MZ) and an increase in the numbers of B cells in the red pulp of the spleen. The expansion of both PALs and follicular/germinal centers during xenograft rejection is comparable to that observed during allograft rejection. We also investigated the effect of two immunosuppressants, leflunomide and cyclosporine, on the spleen of rats with hamster hearts. Leflunomide, which prevents acute xenograft rejection, prevented the increase in PALs and significantly reduced the areas comprising the MZ and follicles. Cyclosporine, which does not alter the tempo of xenograft rejection and only partially inhibited xenospecific antibody production, inhibited the increase in PALs and the appearance of germinal centers, while permitting a modest increase in the area of MZ and follicles. CONCLUSIONS: These observations collectively suggest that both T cell-dependent and T cell-independent responses are stimulated by the transplanted xenograft. However, the T cell-independent responses that initiate xenograft rejection are characterized by very modest increases in the area of MZ and follicles within the white pulp of the spleen.

Animals↗