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At least 127 records · Page 7Linked to original sources

PubMed1986

Distribution of 125I-insulin in cardiocytes at steady state binding conditions at 37 degrees C.

The distribution of 125I-insulin in cardiocytes was analyzed by light microscope autoradiography. Semithin sections were used to distinguish between surface-bound and internalized tracer. At 37 degrees C, when steady state binding conditions were reached, 40 to 60% of the cell-bound tracer was located in the plasma membrane region and the remainder was in the cell interior. Autoradiograms of whole cells were used to study the distribution of tracer molecules on the cell surface. Because Poisson distributions of silver grains were observed on 90% of the cells, it was concluded that the distribution of the insulin-receptor complexes was close to random. In contrast to the findings of Schlessinger et al., no aggregation of insulin-receptor complexes into patches was observed.

Animals↗

PubMed1989

Graphical and statistical approaches to data analysis for in situ hybridization.

Quantification of gene expression in a morphological context is an invaluable tool for neurobiological investigation. The ability to measure the quantity of specific mRNA molecules at the level of the single neuron permits one to monitor the modulation of complex cell synthetic activity of intact neuron populations. The cells of interest can be contiguous or dispersed in functionally significant patterns throughout a broad anatomical region of the brain. The application of quantitative in situ hybridization is technically difficult and labor intensive. Nevertheless, it has great utility for investigating gene expression from a structural perspective. (1) In situ hybridization permits one to ask questions concerning the anatomical pattern of neuronal gene expression. (2) It permits analyses concerning the initiation of expression, cell location, cell type, and alterations of level of expression within a spatial and temporal context. (3) In cases where blotting methods suggest a message exists at low copy, in situ hybridization permits queries at the single-cell level. For example, in situ hybridization can determine if very few cells are expressing the gene product or if many neurons dispersed throughout a brain region exhibit low mRNA copy number/cell. Quantitative analyses also allow detailed investigation of cell response to physiologically meaningful stimulation. Our application of statistical and numerical methods is a demonstration of the utility of probabilistic models; the mixture distribution accounted for data from both labeled and unlabeled sources. In agreement with many previous investigations, grain density over an unlabeled uniform source (oxytocinergic cells) was suitably described by the Poisson distribution. The population of labeled vasopressinergic cells, however, was best described by the negative binomial distribution. Previous investigations from different fields of biology show that the negative binomial can be used to describe many biological phenomena, and this distribution was considered in at least two previous investigations to evaluate autoradiographic data which did not fit the Poisson function. From a theoretical perspective, the probabilistic relationship between beta-particle decay (a Poisson function) and the distribution of message levels among individual neurons in a cell group (gamma distribution) prompts consideration of the negative binomial. For both data sets the observed variances were larger than the mean, and the labeled portion of the data sets exhibited positive skewness.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1985

The anion selectivity of GABA-mediated post-synaptic potentials in mouse hippocampal cells.

Intracellular recordings were made from CA1 and dentate cells of the mouse hippocampal slice. When potassium acetate was used to fill the electrodes, spontaneous synaptic activity was rarely seen in CA1 or dentate cells. In contrast, when electrodes filled with potassium chloride were used, spontaneous depolarizing post-synaptic potentials (p.s.p.s) were prominent. That these p.s.p.s were mediated by gamma-aminobutyric acid (GABA) was supported by the following: they were blocked by electrophoretic application of bicuculline methiodide; their appearance was associated with the reversal of the evoked GABA-mediated recurrent inhibitory post-synaptic potential (i.p.s.p.) and their appearance was associated with the positive displacement of the reversal potential for the response to GABA applied by electrophoresis close to the cell soma. The interval distribution for the p.s.p.s could not be fitted by a Poisson distribution. The anionic selectivity of the conductance evoked by GABA was investigated by using the potassium salts of a range of anions to fill the electrodes. Depolarizing spontaneous p.s.p.s were seen in all cells impaled with electrodes containing potassium chloride, iodide, bromide, nitrate, or chlorate. In these cells, the reversal potential for the response to electrophoretically applied GABA was displaced in the depolarizing direction and the evoked recurrent i.p.s.p. was reversed. When anions with hydrated shells larger than chlorate (bicarbonate, sulphate, chromate, acetate or citrate) were used, spontaneous depolarizing p.s.p.s were not seen, and the reversal potential for the response to somatic GABA application and for the evoked recurrent i.p.s.p. lay between -70 and -75 mV.

Action Potentials↗

PubMed1978

The distribution of bumps in the tail of the locust photoreceptor afterpotential.

An extended tail or prolonged depolarizing afterpotential (PDA) follows the receptor potential of a locust retinula cell when the stimulating light is in the intensity range that saturates the receptor potential. The amplitude and duration of this afterpotential depend on the intensity and duration of the stimulus. As the afterpotential decays, apparently exponentially, it becomes resolved into bumps, which we call light-induced dark bumps (LID bumps). The intervals between light-induced dark bumps are distributed in a way that is indistinguishable from a random (Poisson) distribution. As previously demonstrated, LID bumps are indistinguishable from bumps directly induced by low intensity light in light-adapted cells, which in turn grade into the slightly larger bumps produced, each by a single photon, in dark-adapted cells. The light-induced dark bumps continue for up to an hour in darkness, slowly becoming like dark-adapted bumps in amplitude and shape. To account for the random occurrence and discrete features of bumps after so long a latency, we propose that intense light generates a significant amount of an intermediate molecule or packet which decays slowly to start the same process that normally generates bumps with a short delay.

Animals↗

PubMed1981

[Frequency of chromosome aberrations induced in human peripheral lymphocytes by in vitro 60Co gamma quanta at doses of 1 to 5 Gr. in an analysis of the 1st-division cells at different fixation times].

The quantitative analysis of chromosomal aberrations in the first division cells of 50-, 54-, 58-, 52- and 66-hour peripheral blood lymphocytes cultures of healthy donors was performed after irradiation in vitro with 60Co gamma-quantums at doses 1--5 Gy. Cells of the first division were identified by a differential staining of sister chromatid method using 5-bromdeoxyuridine. No significant differences in frequencies of aberrant cells and aberrations of chromosomal type were found between cultures fixed at different times. The distribution of dicentrics in cells did not differ from the Poisson distribution regardless of fixation times and doses. On the basis of these findings it is concluded that chromosomes of human peripheral blood lymphocytes passing the cell cycle at different rates have approximately equal radiosensitivity.

Chromosome Aberrations↗

PubMed1988

Comparison of frequency distributions in flow cytometry.

A number of methods have previously been considered for the statistical comparison of flow cytometric frequency distributions. For two distributions, the foremost of these is the Kolmogorov-Smirnov (K-S) test, which has been criticized as "too sensitive." We discuss some alternative methods based on the Poisson distribution. The assumption of Poisson variation within channels allows the use of channel-by-channel confidence intervals and chi-square tests. These are simple and more appropriate for discrete data than the K-S test. Graphical displays of these and other techniques are presented. We also attempt to set the problem in an appropriate context. We argue that any statistical procedure must rest on a reasonable understanding of the nature of the variability in the system. This understanding takes the form of an appropriate probability model, which may be approximate but must provide a reasonably accurate description of the data. Incomplete understanding of the data can lead to inappropriate analysis. We discuss the assumptions that underlie our techniques and consider extensions to more complex situations.

Flow Cytometry↗

PubMed1988

Mitosis counting in seminoma: an exercise of questionable significance.

Two pathologists reviewed and classified 45 cases of testicular seminoma, evaluating each case for multiple histologic variables, including mitotic rate. In addition to recording the mitotic count for each of thirty 0.1963-mm2 high-power fields, the investigators recorded the distribution of mitotic counts in many non-spermatocytic seminomas. Statistically significant differences for mitotic rate in the nonspermatocytic tumors were noted between the observers; one observer found a mean mitotic rate of 1.815/high-power field for 43 such tumors, whereas the other noted a mean mitotic rate of 1.388/high-power field (p = 0.001). These differences led to disagreement on the classification of 3 tumors. Of the 4 cases considered to be high-mitotic-rate seminomas by one or both observers, all patients had presented with stage I disease. Three of the patients were followed up for 23, 55, and 56 months, and all were free of disease; the fourth was lost to follow-up. The patient with the highest mitotic rate was free of disease at 55 months of follow-up. On the basis of our findings we question the value of the designation high-mitotic-rate seminoma. Analysis of the distribution of mitotic counts within the tumors revealed them to be Poisson distributed. With these data and other empirically derived data, it was possible to estimate the probability of misclassification of seminoma based on mitotic rate, the diagnostic mitotic rate threshold, and the number of fields counted for mitoses. Similar analysis might be valuable for other tumors, particularly those of smooth muscle origin, in which mitotic rate is of diagnostic or prognostic value.

Adult↗

PubMed1989

Two kinds of "recombination nodules" in Neurospora crassa.

Two morphological types of recombination nodules, termed early and late, are recognized in Neurospora crassa. Eighty nuclei at different substages were used to determine numbers of nodules per nucleus, distribution of nodules along the nucleolus-organizing chromosome, and distribution of nodules among the two largest chromosomes. Early nodules appear at the synaptonemal complex at early zygotene and increase in number during zygotene until a dramatic reduction occurs at zygotene-pachytene transition. Thereafter early nodules are steadily eliminated until they disappear by diplotene. Late nodules are also present during zygotene. Their number doubles at the zygotene-pachytene transition and stays at this level until diplotene. The total number of nodules is rather constant through zygotene and pachytene. Distribution of bivalents with 0, 1, 2, etc. nodules follows a Poisson distribution at zygotene, but not at pachytene, where variance is less than the mean, indicating positive interference. Nodules are distributed nonrandomly along the nucleolus-organizer bivalent. The pattern differs slightly in nuclei of different origin. Nuclei with unusual synaptonemal complexes sustain normal levels of recombination by having the same amount of nodules as normal nuclei. In abnormal nuclei nodules are preferentially associated with normal segments. It is proposed that early nodules do not participate in any form of recombination but have a role in finding an appropriate site for a crossing-over event. Morphological change to the late type indicates that the site has been reached and the exchange event can be mediated by the late nodule.

Chromosomes↗

PubMed1987

Sampling and distribution of Anopheles quadrimaculatus immatures in rice fields.

Dipper samples of Anopheles quadrimaculatus immatures from stocked enclosures in Arkansas rice fields were used to develop regression equations relating dipper sample counts to absolute density. Confidence limits were developed for mean number of immatures collected at each density and stadia, including combined stadia. These data can be used to estimate absolute density from mean dipper count. Distribution of rice field immatures approximated but did not fit the Poisson distribution. Sample size was calculated for 10, 25 and 50% of the true mean, at various levels of Type I and II error. A sample size of N = 6,424 was necessary to detect differences within 10% of the true mean, with 5 and 10% probability of Type I and II error, respectively.

Agriculture↗

PubMed1978

The application of a Poisson model to the annual distribution of daily mortality at six Montreal hospitals.

The daily distributions of annual mortality for varying numbers of years between 1965 and 1975 were investigated in three geriatric hospitals and three general hospitals in the Montreal area. Nearly all the observed mortality distributions were found to mimic the classical Poisson distribution, with little departure. In two of the larger hospitals, the matching of the daily mortality distributions with their Poisson models met stringent statistical criteria. In one of them it was even possible to predict the expected mortality frequencies merely from a knowledge of the annual totals. The remaining four hospitals, which included the three geriatric institutions, also exhibited mortalities regarded as highly suggestive of Poisson distributions, although in one of the geriatric hospitals the mortality distribution tended to be somewhat erratic in this respect.

Aged↗

PubMed1979

The labelling of vesicles in frog endothelial cells with ferritin.

1. The labelling of endothelial cell vesicles with ferritin has been investigated by electron microscopy. Single capillaries in the frog mesentery have been perfused with solutions of known concentrations of ferritin for known periods before fixing the tissue in situ by superfusion with osmium tetroxide. 2. At 17 degrees C, the percentage of lumenal vesicles labelled with ferritin increased as the period of perfusion was increased up to 16 sec prior to fixation. When perfusions were longer than 16 sec, the percentage of vesicles labelled with ferritin remained fairly constant at 70%. 3. At 3 degrees C, no more than 25% of the lumenal vesicles were labelled during the first 30 sec. 4. After correcting the data for losses of ferritin due to sectioning, the distribution of ferritin molecules in the lumenal vesicles was consistent with a Poisson distribution. 5. After perfusions of 16 sec or longer, the number of ferritin molecules per labelled vesicle was roughly three to four times less than would be predicted from the lumenal concentration. 6. At all times there was a gradient of vesicles labelled with ferritin across the endothelial cells, i.e. the percentage of lumenal vesicles labelled was greater than that for cytoplasmic vesicles which in turn was greater than that for vesicles at the ablumenal surface. 7. Whereas the labelling of lumenal vesicles from zero time up to 16-20 sec, the main increase in labelling of cytoplasmic vesicles occurred between 10 and 20 sec. 8. It is concluded that there is a major diffusion barrier to ferritin molecules either close to the endothelial cell surface or across the necks of the lumenal vesicles. It also appears that ferritin molecules do not have access to vesicles during the latter part of their residence at the lumenal surface.

Animals↗

PubMed1986

Determination of the baseline sister chromatid exchange frequency in human and mouse peripheral lymphocytes using monoclonal antibodies and very low doses of bromodeoxyuridine.

We measured the frequency of sister chromatid exchanges (SCEs) in human and mouse peripheral lymphocytes using doses of bromodeoxyuridine (BrdU) ranging from 30 nM to 100 microM (human) and from 10 nM to 10 microM (mouse). Heparinized peripheral blood was obtained from five healthy nonsmokers and from six C57B1/6 male mice. The blood was stimulated with PHA (human) or lipopolysaccharide (LPS, mouse) and grown for the first of two cell cycles in BrdU. Metaphase chromosomes were denatured and exposed to a monoclonal antibody reactive to single-stranded DNA containing BrdU. A second antibody was used to label the first antibody with fluorescein, and propidium iodide was used as a counterstain. Second-division metaphases were thus differentially stained red to indicate DNA content and yellow-green to indicate the presence of BrdU. The results indicate that the baseline SCE frequency in human and mouse peripheral lymphocytes is 3.6 and 2.4 SCEs per cell per generation, and that in the human these frequencies are invariant at the lowest BrdU levels. This suggests that SCEs are an integral part of DNA replication, even in the absence of agents known to induce SCEs. The distribution of SCEs per chromosome was analyzed and found to be Poisson-distributed in all 24 murine cultures and in 25 of 36 human cultures. The distribution of SCEs per chromosome may be due to either species-specific chromosome packaging or to karyotypic differences between the species.

Animals↗

PubMed1992

Induction by H2O2 of DNA and interphase chromosome damage in plateau-phase Chinese hamster ovary cells.

The induction by H2O2 of DNA breaks, DNA double-strand breaks (DSBs), and interphase chromatin damage and their relationship to cytotoxicity were studied in plateau-phase Chinese hamster ovary (CHO) cells. Damage in interphase chromatin was assayed by means of premature chromosome condensation (PCC); DNA DSBs were assayed by nondenaturing filter elution (pH 9.6), and DNA breaks by hydroxyapatite chromatography. Cells were treated with H2O2 in suspension at 0 degrees C for 30 min and treatment was terminated by the addition of catalase. Concentrations of H2O2 lower than 1 mM were not cytotoxic, whereas concentrations of 40 and 60 mM reduced cell survival to 0.1 and 0.004, respectively. An induction of DNA breaks that was dependent on H2O2 concentration was observed at low H2O2 concentrations that reached a maximum at approximately 1 mM; at higher H2O2 concentrations induction of DNA breaks either remained unchanged or decreased. Damage at the chromosome level was not evenly distributed among the cells, when compared to that expected based on a Poisson distribution. Three categories of cells were identified after exposure to H2O2: cells with intact, control-like chromosomes, cells showing chromosome fragmentation similar to that observed in cells exposed to ionizing radiation, and cells showing a loss in the ability of their chromatin to condense into chromosomes under the PCC reaction. The fraction of cells with fragmented chromosomes, as well as the number of excess chromosomes per cell, showed a dose response similar to that of DNA DSBs, reaching a maximum at 1 mM and decreasing at higher concentrations. The results indicate that induction of DNA and chromosome damage by H2O2 follows a complex dependence probably resulting from a depletion of reducing equivalents in the vicinity of the DNA. Reducing equivalents are required to recycle the transition metal ions that are needed to maintain a Fenton-type reaction. The absence of cell killing at H2O2 concentrations that yielded the maximum amount of DNA and chromosome damage suggests that this damage is nonlethal and repairable. It is suggested that lethal DNA and chromosome damage is induced at higher concentrations of H2O2 where cell killing is observed by an unidentified mechanism.

Animals↗

PubMed1989

Diurnal pattern and behavior of oviposition of Toxorhynchites theobaldi in the field.

The diurnal pattern and oviposition behavior of Toxorhynchites theobaldi natural populations were studied in 25 artificial containers in the field. The mosquito exhibited a bimodal oviposition pattern with the lower peak at 1100 hr and a mean of 15.7 eggs per container. The higher peak was observed at 1900 hr with a mean of 80.9 eggs per container. Each female flew from 21 to 58 elliptic vertical circles before ejecting one egg upon the surface. In 270 oviposition events, the average was 31.4 ellipses, and the frequency distribution of flights number with different ellipse numbers was fitted to a Poisson distribution. There was a significant linear correlation (r = 0.70) between the oviposition rate and the container surface area.

Aedes↗

PubMed1991

Bestatin-induced enhancement of in vivo phagocytosis determined by a new simple assay.

Pretreatment of mice by the immunostimulator bestatin resulted after four days in a significant enhancement of the phagocytic activity of peritoneal cells. For quantification of the phagocytic process of murine peritoneal phagocytes a new in vivo assay is proposed. Fluorescein isothiocyanate (FITC)-labeled Escherichia coli bacteria were i.p. injected. After ten minutes peritoneal cells were harvested and the phagocytic index of peritoneal phagocytes was fluorescence-photometrically assessed. The frequency distribution of phagocytized bacteria per cell found by the this assay corresponded to Poisson distribution. This coincidence allowed estimation of the minimum number of cells needed for detecting a significant difference of phagocytosis indices, resulting in an enhancement of test efficiency.

Adjuvants, Immunologic↗

PubMed1988

Studies on the growth of mast cells in rats. Changes in granule size between 1 and 6 months.

Mast cells from rats aged 1 month, 3 months and 5 to 7 months were compared with respect to cell size and secretory granule size and number. With increasing age there was an increase in mean total cell volume accounted for almost entirely by an increase in mean total granule volume/cell even though there was no apparent increase in the number of granules. An increase in histamine content closely paralleled the increase in total granule volume. In each age group, the distribution of equivalent volumes of granule profiles exhibited periodic multimodality consistent with a Poisson distribution of granule volume. We have interpreted these observations in terms of a model in which total granule volume/cell increases through the production of unit granules of uniform size; the increasing size of individual granules we attribute to the fusion of unit granules with each other and with larger granules.

Aging↗

PubMed1989

Micronucleus formation in 2-cell embryos after in vitro X-irradiation of mouse spermatozoa.

Mouse spermatozoa were exposed in vitro to various X-ray doses and added to a medium containing superovulated oocytes. The percentage of fertilized oocytes was determined 24 h after sperm addition and 2-cell embryos were investigated for micronucleus formation. The fertilization rate was drastically decreased after exposure to 470 cGy whereas smaller doses had no effect. The dose-response relationship for micronucleus formation per embryo was linear-quadratic and the number of embryos with micronuclei increased linearly with dose. The distribution of micronuclei among 2-cell embryos showed a significant overdispersion relative to the Poisson distribution after sperm irradiation for doses above 188 cGy.

Animals↗

PubMed1987

Convergence of the maximum likelihood reconstruction algorithm for emission computed tomography.

Convergence properties of the maximum likelihood estimator (MLE) for emission computed tomographic (ECT) image reconstruction are evaluated as a function of Poisson noise, precision of the assumed system resolution model and iteration number up to 10,000 iterations. In the ECT reconstruction problem, the photon-emitting source distribution is to be estimated from measurements of projections of the emitted photon flux. The MLE algorithm seeks a source distribution which will maximise the maximum likelihood function relating the estimated and the measured projections. A Monte Carlo model of the system transfer function of a single photon emission computed tomographic (SPECT) system allowed realistic projection data to be simulated from a known source distribution. Poisson noise was added to the Monte Carlo simulations. By using projection data from a known source distribution generated through a known system transfer function, we were able to simultaneously evaluate the convergence of both the projection estimations as well as the source distribution estimations. As predicted by theory, the estimates of the projections did continue to improve (or remain the same) for all combinations of Poisson noise (up to 10% RMS) and system resolution (+/- 10% of true value) tested. Convergence of source distribution estimates to the true value was found for up to 10,000 iterations only for low noise (0.1% RMS) with the correct resolution function. For all other combinations, there was some optimum iteration (between 30 and 400) after which the source estimate was degraded even though the estimate of the projections was improved.

Algorithms↗