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Biomedical subjects

S H Chan

Publications and source records attributed to S H Chan.

At least 19 recordsLinked to original sources
PubMed1979

Morphine suppression of substantia nigra zona reticulata neurons in the rat: implicated role for a novel striatonigral feedback mechanism.

In lightly anesthetized rats, systemic administration of morphine exerted a naloxone-reversible suppression of spontaneously discharging neurons located primarily in the substantia nigra zona reticulata, either at rest or after their activation by microinjection of dopamine into the caudate nucleus. Inactivation of these neurons within the striatonigral feedback pathway is suggested to complement a direct action on the nigrostriatal dopaminergic cells by the opiate, resulting in the morphine suppression of caudate neuronal activities.

Animals↗
PubMed1979

Analysis of electrophoretic behavior of cytochrome c oxidase subunits. Retardation coefficient versus molecular weight in dodecyl sulfate urea gels.

1. Standard proteins were examined by electrophoresis in highly cross-linked polyacrylamide gels containing sodium dodecyl sulfate and urea. Their behavior was analyzed at a single gel concentration (by molecular weight vs. relative mobility) and at several gel concentrations (molecular weight vs. retardation coefficient). The validity of the latter method of analysis was established for this gel system. 2. Cytochrome c oxidase was subjected to analysis by this method. Compared to standards, subunits I and III showed increased free electrophoretic mobility, while that of subunit V was slightly decreased. The molecular weight values derived were: I, 44 600; II, 22 700; III, 23 500; IV, 16 900; V, 9400; VI, 7600; VII, 4300. The standard errors were all less than +/- 7%. 3. Isolated V and VI were analyzed by two dimensional dodecyl sulfate electrophoresis, in which the second dimension also contained urea. In contrast to their behavior when the holo-enzyme was examined, these isolated subunits V and VI no longer exchange migrating positions relative to each other during the two dimensional analysis. The molecular weight values of the isolated subunits agree with those of the holo-enzyme.

Animals↗
PubMed1979

Histopathology of nasopharyngeal carcinoma: correlations with epidemiology, survival rates and other biological characteristics.

A total of 363 cases of nasopharyngeal carcinoma (NPC) in Singapore were classified into squamous cell carcinoma (SCC; 73 cases), non-keratinizing carcinoma (NKC; 178 cases) and undifferentiated carcinoma (UC; 172 cases). Possible biological differences between these histologic types and between tumors with and without lymphocytic infiltration were investigated by correlations with survival rates and with selected epidemiologic, immunovirologic, and immunogenetic data on the disease. The 5-year survival rates following radiotherapy were 25.3% for all cases and 58.8% for tumors restricted to the nasopharynx. The 5-year survival rate for SCC was poorer than for the combined NKC and UC groups (p less than 0.05). The 3-year survival rate was better for tumors with lymphocytic infiltration (p less than 0.05), but there were no differences in the 5-year survivals. The survival rates were better in females (p less than 0.01) and in the younger age groups (p less than 0.01). There were no significant correlations between histopathology of NPC and the distributions of cases by age, sex, HLA antigen profiles, or cell-mediated immune status. Squamous cell carcinoma was associated with lower levels of antibodies to the Epstein-Barr nuclear antigen (p less than 0.05), but there were no differences with respect to antibodies against other EBV related antigens. These findings support the view that SCC, NKC, and UC of the nasopharynx, as defined in the WHO classification, are variants of a fairly homogeneous group of neoplasms in the Singapore population.

Adolescent↗
PubMed1979

A comparison of the prognostic value of antibody-dependent lymphocyte cytotoxicity and other EBV antibody assays in Chinese patients with nasopharyngeal carcinoma.

Antibody titres to EBV-associated antigens in Chinese NPC patients were analysed according to length of survival after diagnosis and to disease stage. Geometric mean titres of ADLC antibody were highest in the long-term survivors, whereas VCA, EA and EBNA antibody titres showed an inverse relationship to survival. High VCA, EA and EBNA titres were less frequent, and high ADLC titres were more frequent in long-term survivors than in intermediate or short-term survivors. The association of geometric mean titres of EBV antibodies with prognosis could not be entirely explained by stage of disease. A functional role for the ADLC antibody is suggested by the association of a high ADLC antibody titre with a good prognosis regardless of stage of disease.

Antibodies, Viral↗