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L Y Cheng

Publications and source records attributed to L Y Cheng.

At least 37 records · Page 2Linked to original sources
PubMed1994

Film autoradiography identifies unique features of [125I]3,3'5'-(reverse) triiodothyronine transport from blood to brain.

1. Steady-state iodothyronine profiles in plasma are composed of thyroid gland-synthesized hormones (mainly thyroxine) and tissue iodothyronine metabolites (mainly triiodothyronine and reverse triiodothyronine) that have entered the bloodstream. The hormones circulate in noncovalently bound complexes with a panoply of carrier proteins. Transthyretin (TTR), the major high-affinity thyroid hormone binding protein in rat plasma, is formed in the liver. It is also actively and independently synthesized in choroid plexus, where its function as a chaperone of thyroid hormones from bloodstream to cerebrospinal fluid (CSF) is undergoing close scrutiny by several groups of investigators. Because TTR has high-affinity binding sites for both thyroxine and retinol binding protein, its potential role as a mediator of combined thyroid hormone and retinoic acid availability in brain is of further interest. 2. While they are in the free state relative to their binding proteins, iodothyronines in the cerebral circulation are putatively subject to transport across both the blood-brain barrier (BBB) and choroid plexus CSF barrier (CSFB) before entering the brain. Previous autoradiographic studies had already indicated that after intravenous administration the transport mechanisms governing thyroxine and triiodothyronine entry into brain were probably similar, whereas those for reverse triiodothyronine were very different, although the basis for the difference was not established at that time. Intense labeling seen over brain ventricles after intravenous administration of all three iodothyronines suggested that all were subject to transport across the CSFB. 3. To evaluate the role of the BBB and CSFB in determining iodothyronine access to brain parenchyma, autoradiograms prepared after intravenous administration of [125I]-labeled hormones (revealing results of transport across both barriers) were compared with those prepared after intrathecal (icv) hormone injection (reflecting only their capacity to penetrate into the brain after successfully navigating the CSFB). 4. Those studies revealed that thyroxine and triiodothyronine were mainly transported across the BBB. They shared with reverse triiodothyronine a generally similar, limited pattern of penetration from CSF into the brain, with circumventricular organs likely to be the main recipients of iodothyronines (with or without retinol) transported across the CSFB. 5. Analysis of all of the images obtained after intravenous and icv hormone administration clarified the basis for the unique distribution of intravenously injected reverse triiodothyronine. The hormone is excluded by the BBB but may be subject to limited penetration into brain parenchyma via the CSF. 6. Overall the observations single out reverse triiodothyronine as the iodothyronine showing the most distinctive as well as the most limited pattern of transport from blood to brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Studies of epidermal growth factor (EGF) receptor in plasma membrane from rat liver and hepatoma tissues.

Plasma membrane purified from Buffalo rat liver tissue not only had the ability to bind 125I-EGF (2.77 pg of EGF/mg of membrane protein), but also exhibited both high (Kd = 0.08 nM) and low (Kd = 5.67 nM) affinity receptors. However, the binding of EGF to hepatoma plasma membrane was insignificant. EGF receptor in plasma membrane from normal liver tissue was identified by ECL Western blotting using monoclonal anti-EGF receptor antibody and phosphorylated via the stimulation of EGF. This phosphorylation was inhibited by genistein, a tyrosine kinase inhibitor. However, these effects were not observed in hepatoma cell membrane. These results suggest that plasma membrane purified from normal rat liver tissue has a high level of functional EGF receptor, whereas, hepatoma plasma membrane lacks the receptor.

Animals↗
PubMed1993

Psychotherapy supervision in Hong Kong: a meeting of two cultures.

The experience of psychotherapy supervision of a group of trainee psychiatrists, in a university setting in Hong Kong, is reported from the supervisor's perspective. The trainees showed difficulties in this exercise. The cultural difference between the supervisor and the trainees, and that between the Western psychotherapy culture and the Chinese culture, is discussed. It is then followed by a description of what is seen as the trainees' resistance in the acceptance of psychotherapy and of the supervisor. This is considered to be one of the problems in the transcultural application of psychotherapy, and has to be overcome if this importation is to be successful.

Cross-Cultural Comparison↗
PubMed1993

Two new rat alpha-globin sequences as identified by the conserved region PCR.

Based on the notion that regions of structural genes which encode critical domains of the corresponding proteins are highly conserved among closely related species, oligonucleotide primers were designed and used to amplify the alpha-globin sequence(s) of the Sprague-Dawley (SD) rat. Data of these amplified sequence constructs showed that two new rat alpha-globin specific sequences have been identified. Southern hybridization confirmed the presence of these sequences in the rat genome.

Animals↗
PubMed1992

Inhibition of alcohol dehydrogenases by thiol compounds.

2-Mercaptoethanol is a strong inhibitor of LADH. The inhibitory effect is likely due to the binding of the SH group to the enzymatic zinc ion. Various thiol compounds do not inhibit YADH and it is suggested that the zinc atoms involved in the catalytic mechanism of LADH and YADH may have different structural arrangements and that these zinc atoms in YADH may not be blocked by thiol compounds. Thiol compounds also quench the enhanced fluorescence of LADH-NADH in a pH-dependent manner. At pH 9.2, the binding of coenzyme to LADH is replaced by 2-mercaptoethanol, whilst at pH 7.3, it further quenches the fluorescence of NADH-LADH. This quenching of fluorescence is likely attributed to a conformational change and energy transfer upon binding of 2-mercaptoethanol to the LADH-NADH complex. Complete reversal of the inhibitory effect of thiol compounds on LADH can be obtained by dialysis.

Alcohol Dehydrogenase↗
PubMed1991

On the advantages of cross-culture psychotherapy: the minority therapist/mainstream patient dyad.

The personal quality of the therapist is a key element in therapy. In the case of the minority therapist, the difference in language and cultural background offers the patient unique benefits. Value orientations amongst cultures are similar enough for the minority therapist to acculturate. Through acculturation, the therapist becomes aware of a new set of value orientations. This cultural objectivity better enables the therapist to help the mainstream patient to see alternatives in coping with stresses of life, and to fortify the patient's adaptive skills. Because Western psychiatry and psychotherapy are culture-bound, mainstream therapists may easily be "culturally addicted," whereas a minority therapist can maintain cultural neutrality. Advantages discussed include language independence, culture independence, positive transference and analogous experiences.

Cross-Cultural Comparison↗
PubMed1989

Vesicle formation in the Golgi apparatus.

In this paper we examine the mechanics of vesicle budding from the Golgi apparatus. We propose a model for this process based on the notion that molecular surfactants can release the elastic energy stored in the lipid bilayer. The same physical process may drive other vesiculation processes, including coated vesicle formation and budding of enveloped viruses from the plasma membrane.

Golgi Apparatus↗
PubMed1989

[Effect of chang chun dan on noradrenaline levels of the brain and plasma in aged rats].

In this paper, the rats were randomly divided into three groups: (1) Young (Y); (2) Aged (A); (3) Aged rats treated with Chang Chun Dan (AT) for 3 months. The level of noradrenaline (NA) in brain and plasma of three group rats had been examined by radioenzymatic assay. The changes of fluorescent intensity of NA in locus coeruleus had been observed by histochemical method. The levels of NA in hypothalamus of three groups were 162 +/- 9.93, 209 +/- 13.2, 167 +/- 11.8 ng/g wet tissues and in plasma were 1.29 +/- 0.16, 0.84 +/- 0.08, 0.96 +/- 0.08 ng/ml respectively. The results showed that the NA level of hypothalamus in AT group was lower than that of A group (P less than 0.05), and the NA level in Y group was raised markedly comparing with A group (P less than 0.01). The plasma NA level in A group was significantly lower than that in Y group (P less than 0.05). The NA level in AT group was raised a little comparing with A group. But the fluorescent intensity of NA in locus coeruleus between AT and A group was no difference. The results suggested that the changes of neurotransmitter induced by Chang Chun Dan may be basis of delaying aging effect and improving symptom of Kidney deficiency induced by aging.

Aging↗
PubMed1987

Deformation analyses in cell and developmental biology. Part I--Formal methodology.

This study presents a computational approach for the deformation analyses of problems in cell and developmental biology. Cells and embryos are viewed mechanically as axisymmetric shell-like bodies containing a body of incompressible material. The analysis approach is based on the finite element method. It is comprised of three finite element ingredients: an axisymmetric shell/membrane element valid for modeling finite bending, shearing and stretching; a volume constraint algorithm for modeling the membrane-bound incompressible material; and a contact algorithm for modeling the mechanical interactions between deformable bodies. Part II of this study will demonstrate how these three ingredients can be applied to analyze mechanical experiments on cells. This same method is also useful for simulating embryonic shape changes during development.

Algorithms↗
PubMed1987

Deformation analyses in cell and developmental biology. Part II--Mechanical experiments on cells.

This study employs the finite element approach developed in Part I to analyze mechanical experiments on cells. It views cells as axisymmetric membrane structures containing a body of incompressible material, and models the mechanical contact between a cell and the loading apparatus by a contact algorithm. Since the method is valid for analyzing axisymmetric shell-like bodies with arbitrary shapes, it treates various mechanical experiments on cells in a unified manner. For demonstration purposes, three commonly used mechanical experiments on cells are considered; the compression experiment; the suction (micropipette aspiration) experiment; and the magnetic particle experiment. Based on an estimate of the mechanical property data for unfertilized sea urchin eggs, this analysis method predicts the responses for all three experiments using the same assumptions and approximations. This parallel treatment gives a broad basis for data correlation with experiments. The method also provides insights into mechanical experiments not offered by other approximate methods. For example, it gives the distributions of tensions and stretches on the cell cortex, and suggests the role of friction in the suction experiment.

Animals↗
PubMed1986

Neurulation and the cortical tractor model for epithelial folding.

We present here a new model for epithelial morphogenesis, which we call the 'cortical tractor model'. This model assumes that the motile activities of epithelial cells are similar to those of mesenchymal cells, with the added constraint that the cells in an epithelial sheet remain attached at their apical circumference. In particular, we assert that there is a time-averaged motion of cortical cytoplasm which flows from the basal and lateral surfaces to the apical region. This cortical flow carries with it membrane and adhesive structures that are inserted basally and resorbed apically. Thus the apical seal that characterizes epithelial sheets is a dynamic structure: it is continuously created by the cortical flow which piles up components near where they are recycled in the apical region. By use of mechanical analyses and computer simulations we demonstrate that the cortical tractor motion can reproduce a variety of epithelial motions, including columnarization (placode formation), invagination and rolling. It also provides a mechanism for driving active cell rearrangements within an epithelial sheet, while maintaining the integrity of the apical seal. Active repacking of epithelial cells appears to drive a number of morphogenetic processes. Neurulation in amphibians provides an example of a process in which all four of the above morphogenetic movements appear to play a role. Here we reexamine the process of neurulation in amphibians in light of the cortical tractor model, and find that it provides an integrated view of this important morphogenetic process.

Amphibians↗