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Biomedical subjects

I Levin

Publications and source records attributed to I Levin.

At least 55 records · Page 3Linked to original sources
PubMed1990

Molecular analysis of endogenous virus ev21-slow feathering complex of chickens. 1. Cloning of proviral-cell junction fragment and unoccupied integration site.

Sex-linked slow-feathering gene, K, is genetically associated with the presence of an avian endogenous retrovirus ev21 in White Leghorns (WL). An EcoRI fragment corresponding to the endogenous virus ev21-cell junction fragment and a fragment homologous to the proviral unoccupied site (US) were cloned, respectively, from genomic DNA libraries of two WL chickens: an ev21-only female and an ev-negative male. A 1.7-kilobase pairs (kbp) fragment cleaved from the cloned proviral US by the HaeIII restriction endonuclease was the most informative probe to molecularly characterize the occupied and unoccupied integration sites of ev21 locus. Restriction fragment length polymorphism analysis of slow-feathering (SF) and rapid-feathering (RF) chickens from various commercial breeds, using the US HaeIII 1.7-kbp probe, indicated that the complete genetic association between ev21 and SF phenotype is common among other lines of SF chickens and was not restricted to WL. It was also shown that there was at least one additional DNA region highly homologous to DNA sequences flanking the EV21 integration site in the chicken genome. In SF birds of either sex this additional repeat was distinguishable from the site occupied by ev21 (OR) and represents an unoccupied repeat (UR). Analysis of DNA from RF revertant females showed novel patterns of reversion. In Type I RF revertants, RF is associated with the complete excision of proviral ev21 DNA sequences. In Type II revertants, the UR homologous to the cell sequences flanking ev21 integration site is excised, but proviral ev21 sequences remain intact. A hypothesis to explain these types of reversion is suggested. It postulates a close association between OR and UR on the Z chromosome.

Animals↗
PubMed1990

Misconceptions about motion: development and training effects.

2 experiments were performed to examine whether children and adults possess a single-object/single-motion intuition. This intuition involves the view that because all parts of a rigid object move together, they all must move at the same speed. We found that third graders, sixth graders, ninth graders, and adults all responded in accord with this intuition. On problems where the intuition led to errors, a large majority of subjects of all ages answered incorrectly. On problems where it led to successful performance, subjects answered more accurately than on problems where the intuition was not applicable. In addition, the specific errors were those that the intuition yielded, and the intuition fit individual patterns of performance. The intuition not only influenced speed judgments but also judgments of distance traveled. Experiment 2 demonstrated that making sixth graders aware of the intuition and providing them kinesthetic experience that contradicted it produced significant improvements in the children's understanding. Implications for how scientific misconceptions in general can be overcome were discussed.

Acceleration↗
PubMed1990

Variation of HLA-ABC surface antigen expression on adenocarcinoma of the colon in correlation with the degree of differentiation.

The expression of HLA class I antigens was tested on biopsy specimens originating from 90 patients suffering from adenocarcinoma of the colon. Three different samples were examined from each specimen: one from the tumor and the other two from the neighboring surrounding surgical margins. Twenty-seven out of 27 well-differentiated carcinomas were found highly positive for the presence of HLA class I antigens. Most of the moderately well differentiated tumors (37 out of 46) were weakly positive. None of the poorly differentiated tumors (n = 11) nor the mucin-producing tumors (n = 6) expressed HLA class I antigens. In 180 histologically normal colonic epithelia from patients suffering from adenocarcinoma of the colon (surgical edges free from tumorous tissue of the same specimens) no positive expressions were found. These results tend to suggest that class I HLA-ABC deficient, poorly differentiated tumors may possibly evade lethal immune aggression by HLA-restricted cytotoxic T cells and thus progress to overt malignancy. This negative expression may provide an explanation for the poorer prognosis observed among patients afflicted by a poorly differentiated adenocarcinoma or mucin-producing adenocarcinoma of the colon. Furthermore, these results tend to suggest that enhanced expression of HLA class I antigens on colonic epithelium could serve as a clinical laboratory indication for further examination looking for the possible emergence of neoplasm. If further verified, this may prove to serve as a predictive diagnostic tool for screening populations at risk.

Adenocarcinoma↗
PubMed1989

Abnormal renal mobility--an indication for surgical intervention.

Movable kidney is a debated entity and therefore not diagnosed in many cases. According to our experience the diagnosis should be made much more frequent in patients who suffer from loin and/or abdominal pain which is relieved by recumbent position. Twenty-nine cases of patients who suffered from loin and/or abdominal pain and were diagnosed as suffering from abnormal renal mobility by medical history, intravenous pyelogram, angiography and dynamic scanning were operated upon with a reported high rate of relief of pain (87%; 25/29). The technique employed was the modified Deming operation.

Abdomen↗
PubMed1989

Effect of prolactin on casein and fat synthesis and casein secretion in explants of bovine mammary tissue pretreated in athymic nude mice.

Bovine mammary gland tissue from 4- to 6-mo-old calves was grafted s.c. (dorsum) to 7- to 9-wk-old female athymic "nude" mice. The graft-bearing mice were divided into three groups and were treated with the following hormonal combinations: 1) implantation of a pellet containing estrogen and progesterone followed by injection of estrogen and progesterone, 2) injections of estrogen and progesterone, and 3) injections of estrogen, progesterone, and prolactin. Following in vivo treatment, the grafts were removed and prepared for organ culture. Explants from each treatment were subdivided into two hormonal regimens: 1) insulin and cortisol; 2) insulin, cortisol, and prolactin. An increase in in vitro fat synthesis was observed in explants cultured in the presence of prolactin. This increase was not affected by previous in vivo hormonal treatment. In vitro casein synthesis was not stimulated by the presence of prolactin in the culture medium; however, casein secretion was elevated in explants from grafts from animals that were treated in vivo with estrogen, progesterone, and prolactin. Casein secretion was further increased in explants cultured in the presence of prolactin but rapidly dropped in its absence. Explants that were not implanted in mice responded in long-term organ culture similarly to explants pretreated in vivo.

Animals↗
PubMed1988

Environmental distribution and long-term dispersion of reactor 14CO2 around two German nuclear power plants.

Carbon-14 data on atmospheric CO2 as well as on plant material (tree leaves and wheat) from the vicinity of two German boiling water reactors (Philippsburg and Isar/Ohu) are reported. Atmospheric CO2 samples taken routinely with an integration time of one or two weeks 1.75 km downwind of the Philippsburg reactor (900 MW electrical power) show a maximum 14C excess concentration of delta 14C (excess) = 300 +/- 7%, corresponding to 12.7 mBq m-3 (STP air). The long-term average excess amounts to delta 14C (excess) = 47 +/- 3%, corresponding to 2.0 mBq m-3 (STP air). The concentrations observed with plant material at the same sampling site range between delta 14C (excess) = 0% and 120%, corresponding to 0 and 27 mBq (g carbon)-1. With the meteorological dispersion parameters actually measured at the nuclear power plants, the dispersion factors for the various sampling sites and for the individual periods of sampling were calculated on the basis of a one-dimensional Gaussian plume model. With the observed 14C excess concentrations and the dispersion factor, a "theoretical" (i.e. calculated) reactor 14C source strength is then determined. For the Philippsburg reactor, which is situated in the flat Rhine valley, the "theoretical" and the observed yearly mean 14C emissions compare rather well (within a factor of 2). A significant systematical deviation from the model was found in the concentration decrease with source distance: the decrease predicted between the 1.75-km and 3.25-km distances is steeper than actually observed. The 14C excess concentrations found in tree leaves around the Isar/Ohu reactor (907 MW electrical power) at 1-2 km distance fall into the same range as observed at Philippsburg. In the hilly terrain at this reactor site, the model calculations agree well with the observed values up to a distance of 1 km if the relative elevation of the sampling site is taken into account by introducing a "reduced stack height" in the model calculations. This method fails in predicting the concentrations at distances greater than 1 km from the source.

Air Pollutants↗
PubMed1987

Squamous cell carcinoma of the renal pelvis with sarcomalike stroma: a light and electron microscopic study with immunohistochemical analysis.

Primary neoplasms of the renal pelvis are rare. Most are malignant, and most of these are transitional cell carcinomas. We report the unusual occurrence of a squamous cell carcinoma with sarcomatoid stroma arising from the renal pelvic mucosa in a patient with renal lithiasis. Immunohistochemical stains for keratin intermediate filaments failed to demonstrate their presence in the spindle cell portion of the tumor. Transmission electron microscopic study did not reveal structures of an epithelial nature in these same cells. Our findings support the contention that the spindle cells of the stroma are not squamous in nature, but represent either a reactive or a neoplastic transformation of these underlying stromal elements.

Carcinoma, Squamous Cell↗
PubMed1987

The use of panoramic radiographs to measure alveolar bone areas.

The purpose of the study was to determine the accuracy of measurements made of the mandible from panoramic radiographs. A comparison was made between measurements made directly from dry mandibles, and measurements made from panoramic radiographs of the same mandibles. The use of linear proportions reduced the errors of successive radiographic observations but failed to reveal left- and right-side differences. A method was developed to demarcate two areas of the radiograph, one of which was defined by the crest of the residual alveolar ridge and the other independent of the alveolar ridge. Both areas were measured and their proportions calculated for each mandible observed. This proportional value was referred to as the Area Index. The method was applied to panoramic radiographs of individuals with complete dentitions. The inter-observation error of the Area Index was found to be 4.9%. It was concluded that, in selected cases, panoramic radiographs can be used to provide information about resorption of the residual mandibular alveolar bone.

Alveolar Process↗
PubMed1987

Thermogenic activity and capacity of brown fat in fasted and refed golden hamsters.

The effects of different food deprivation regimens on the thermogenic activity and capacity of brown adipose tissue in the golden hamster have been investigated. Thermogenesis in the tissue was assessed by measurements of tissue cytochrome-c oxidase activity, mitochondrial GDP binding, and the specific mitochondrial concentration of uncoupling protein. The thermogenic activity and capacity of brown adipose tissue were found to be markedly reduced in fasted or underweight hamsters. Measurements of cytochrome-c oxidase activity indicate that the reductions were caused exclusively by a loss in mitochondrial mass, uncoupling protein concentration and GDP binding to mitochondria remaining unchanged. The decrease in brown adipose tissue thermogenesis was associated with a reduction in the capacity for nonshivering thermogenesis in the whole animal. Hamsters recovered from weight losses without increasing their food intake, and the recovery was accompanied by a normalization in mitochondrial mass in brown adipose tissue. Mitochondrial mass was, however, restored only after 10 days of ad libitum refeeding. These results suggest that the reduction in energy expenditure in the fasted hamster could relate to a decrease in brown adipose tissue thermogenesis, in addition to the previously reported decreases in resting metabolic rate and locomotor activity. Reductions in thermogenesis may also represent a further mechanism by which energy stores recover in the golden hamster without postfast hyperphagia.

Adipose Tissue, Brown↗
PubMed1986

Gender differences in predicting loneliness from social network characteristics.

In two studies we examined gender differences in predicting loneliness from measures of social network structure and a measure of perceived social support. The results showed that social network characteristics, especially density, were consistently better predictors of perceived loneliness for men than for women. Study 1 used the traditional measure of network density in which the number of relationships among network members was determined. Study 2 used a newly developed index of density that assessed the extent of closeness of relationships between pairs of network members. Uniformly, male subjects with more highly interconnected, cohesive sets of friends reported themselves to be less lonely, whereas density had little relation to loneliness in female subjects. These results are discussed as possibly indicating that men and women use different standards in evaluating whether they are lonely. It is suggested that men may use more group-oriented criteria in evaluating loneliness, whereas women focus more on the qualities of dyadic relationships.

Adult↗
PubMed1986

An examination of the relation of individual difference variables to loneliness.

This study investigated the relation of five individual difference variables (extroversion, depression, self-esteem, neuroticism, and attitude toward others) to loneliness. The relative contributions of two different models that might explain these relations were examined. One model suggests that individual difference variables are related to loneliness through the mediation of social network variables; that is, individual difference variables may reduce people's motivation and/or ability to build and maintain social relationships, which in turn leads to loneliness. The second model, the cognitive bias model, states that both the individual difference variables and loneliness are influenced by the same intrapersonal, cognitive processes. Some people are prone to negative affect and tend to evaluate themselves and their relationships negatively. The relations of self-esteem, neuroticism, and depression to loneliness were hypothesized to reflect the cognitive bias model, while extroversion and attitudes toward others were hypothesized to be related to loneliness through the mediation of social network variables. Eighty-two female and 42 male adults completed measures of loneliness and the five individual difference variables, as well as an instrument assessing their social networks. The results indicated partial support for both models for each of the individual difference variables. Together, the two models did a good job of explaining the correlations of the individual difference variables and loneliness. The implications of these findings, as well as their relation to previous research, are discussed.

Adult↗
PubMed1984

The role of memory and integration in early time concepts.

The nature of 5- to 8-year-old childrens ' time concepts was examined by analyzing two possible explanations for the greater difficulty children demonstrate in comparing durations that differ in beginning times as compared to those that differ in ending times. The explanations were (a) poor recall of beginnings as compared to endings due to their lower salience, (b) difficulty in integrating information from both points and reliance on endings only due to their greater salience. The subjects were 630 boys and girls from kindergarten to second grade. The children were presented with a series of two lights in different orders and combinations and were asked to compare order of beginnings and endings, and duration of the two lights. Results contradicted the memory explanation. In addition, repetitious questioning about order of one point (beginning or ending) appeared to have shifted children's attention from that point to the complementary point. Possible sources of children's failure to integrate beginning and end points when comparing durations were discussed.

Attention↗