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Biomedical subjects

R H Stevens

Publications and source records attributed to R H Stevens.

At least 163 records · Page 9Linked to original sources
PubMed1973

Isolation of messenger RNA coding for mouse heavy-chain immunoglobulin.

A method for purification of the mRNA coding for heavy-chain protein of a mouse G(2a) myeloma (5563) is reported. Complete myeloma protein (H(2)L(2)) specifically binds to the heavy-chain mRNA, and the resultant RNA-protein complex is precipitated with antiserum against 5563 myeloma protein. Cytoplasmic RNA isolated by this method showed two bands of 6.0 x 10(5) and 3.1 x 10(5) molecular weight when analyzed by acrylamide gel electrophoresis. The RNA in the bands contained 1.5% and 8% A-rich regions, respectively. The RNA in each of the bands contained sequences for heavy-chain protein when translated in Xenopus laevis oocytes.

Animals↗
PubMed1972

RNA metabolism in HeLa cells at reduced temperature. II. Steps in the processing of transfer RNA.

Incubation of HeLa cells at 24 degrees C results in the modification of the processing of pre-tRNA to tRNA. Both methylation and size reduction were shown to take place in vitro when purified pre-tRNA was subjected to processing in a cytoplasmic extract of HeLa cells The migration of pre-tRNA from the nucleus to the cytoplasm was not significantly altered at 24 degrees C

Cell Fractionation↗
PubMed1971

RNA metabolism in HeLa cells at reduced temperature. I. Modified processing of 45S RNA.

Incubation of HeLa cells at suboptimal temperature has been used to study the synthesis of 45S ribosomal RNA precursor and the individual steps of the subsequent processing to 28S RNA. Below 20 degrees C no detectable 45S RNA is formed. The processing of 45S RNA to 32S RNA ceases around 15 degrees C, and the processing of 32S RNA to 28S RNA is inhibited near 25 degrees C. Prolonged incubation at reduced temperature results in further modification of the processing, resulting in the apparent accumulation of 41S RNA. The products of these reactions at reduced temperature appear normal in that the ribosomal RNA made at 27 degrees C can be isolated from functional polyribosomes in the cytoplasm after a short incubation at 37 degrees C.

Carbon Isotopes↗
PubMedDate not supplied

Radiation equivalency of 1, 2-dimethylhydrazine in rats.

A scale based upon the induction of anti-tumor cellular immune responses has been described which relates the in vivo mutagenic/carcinogenic potential of an environmental agent with that of ionizing radiation. Such a potential (radiation equivalency) has now been determined in rats for the gastrointestinal carcinogen 1, 2,-dimethylhydrazine as compared with the effects induced by X-irradiation of only the small intestine. The preliminary results suggest that such scales may be readily constructed based upon environmental immunology concepts which relate the potential hazard of an agent to be weighed alongside the maximum allowable population limits of ionizing radiation.

Animals↗
PubMedDate not supplied

Artificial neural networks can distinguish novice and expert strategies during complex problem solving.

OBJECTIVE: To determine whether expert problem-solving strategies can be identified within a large number of student performances of complex medical diagnostic simulations. METHODS: Self-organizing artificial neural networks were trained to categorize the performances of infectious disease subspecialists on six computer-based clinical diagnostic simulation that used the sequence of diagnostic tests requested as the input data. Six hundred seventy-six student solutions to these problems were presented to these trained neural networks to determine which, if any, of the student solutions represented those of the experts. RESULTS: For each simulation, the expert performances clustered around one dominant output neurode, indicating that there were common problem-specific features associated with the experts' problem-solving performances. When the performances of students who also made correct problem diagnoses were tested on these expert-trained neural networks, 17% were classified as representing expert strategies, indicating that expert performance was a somewhat rare and inconsistent occurrence among the students. CONCLUSIONS: The ability to identify a small number of expert-like strategies within a large body of student performances may provide an opportunity to study the dynamics of complex learning at both individual and population levels as well as the emergence of medical diagnostic expertise.

Diagnostic Tests, Routine↗
PubMedDate not supplied

Solving the problem of how medical students solve problems.

Although gathering and processing information are essential to medical problem solving, little is known about what strategies students use to gather information or how they use their cognitive skills to solve problems. We have developed computer-based problem-solving exercises in immunology to determine how students gather and process information. Graphic representations of students' search paths through different problems were developed to visualize how organized and focused their knowledge was, how well their organization related to critical concepts in immunology, where serious misconceptions (confusion or erroneous models) occurred, and whether proper knowledge links between conceptual domains existed. With rapid generation and interpretation of information on patterns and difficulties in problem solving, it should become possible to develop a specific and personal approach to each student's educational needs.

California↗
PubMedDate not supplied

Genealogical memory to perinatal iodine-131 exposure in rats: I. Alteration in natural immunity.

A heritable alteration in the natural immunity as measured by changes in the natural killer (NK) cell activities of peripheral blood lymphoid-cells was found to occur in rats upon an in utero exposure to iodine-131. The model that was employed for the measurements consisted of Fischer F344 inbred rats exposed to iodine-131 (sodium) during their 16th to 18th day of gestation. The natural immunity of the animals was evaluated by determining the NK cell activities of peripheral blood lymphoid cells of the offsprings when they reached 2 months of age. Immediately following determination of the natural immunity, brother and sister matings were carried out for evolution of the families. Study of these pedigrees revealed an impairment in the natural immunity to persist through two generations (F1, and F2) of the male animals. The hematological profiles of the animals suggest that the insult may alter the numbers of red and white blood cells in the succeeding generations, but has little noticeable effect upon the percentage of lymphocytes. The interpretation of the results indicate that a perinatal insult by iodine-131 during late gestation can result in both somatic and germ cell changes in the immunological system. Thus, there appears to be a genealogical memory to an in utero radionuclide insult which may adversely affect the offspring's immunological competency to respond to subsequent insults.

Animals↗
PubMedDate not supplied

Post-partum antibody-dependent cell-mediated immunity in the rat following perinatal exposure to iodine-131.

A study was recently completed which indicated the first generation of adult rats that had been exposed perinatally to iodine-131 possessed peripheral blood lymphoid-cells capable of expressing cytotoxicity towards cultured small bowel adenocarcinoma target cells, i.e., active antitumor cell-mediated immunity (CMI). The results gathered during the current investigation suggest that such animals similarly express anti-tumor antibody-dependent cell-mediated immunity (ADCC). The animal model employed consisted of Fisher F344 inbred rats exposed to iodine-131 (sodium) during their 16th to 18th day of gestation, and at an interval of two months post-partum when the offsprings had matured into adults, they and their mothers were evaluated for the presence of serum components capable of expressing ADCC activities toward X-ray induced small bowel adenocarcinoma target cells. Significant ADCC activities were found to be expressed by the offspring while no analogous immunological responses could be detected in the serum of the mothers. This lack of maternal ADCC activity suggests the existence of a biological block developing during pregnancy resulting in the mother being immunological nonresponsive to carcinogenic insults. One serum component present in the offspring identified as being responsible for initiating ADCC was an immunoglobulin of the IgG class as based upon its physical characteristics: solubility, molecular weight, and reactivity with anti-immunoglobulins, pepsin, and protein A. The interpretation of these findings is that perinatal exposure to radioiodine results in the development of cells having foreign-like properties in the offspring which are recognized by the animal's immune system, thus resulting in detectable antitumor CMI and ADCC immune responses.

Animals↗