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PubMed1976

Extraversion and reinforcement in verbal operant conditioning.

The present investigation was designed to study the relationship between extraversion and modes of reinforcement in verbal operant conditioning. A 4 X 3 randomized block design was replicated ten times. Eighty graduate and post-graduate male students were individually subjected to the standard Taffel conditioning procedure. When the numbers of conditioned responses produced by introverts and extraverts were compared, it was found that: (1) under negative reinforcement ('bad' and electric shock), with both the female and male experimenters, and under positive reinforcement ('good') with the male experimenter, the introverts' score was the higher of the two; (2) under positive reinforcement ('good') with the female experimenter, the extraverts' score was higher than that of the introverts.

Adult↗

PubMed1978

Impulsivity/sociability and reinforcement in verbal operant conditioning.

The present investigation was designed to study the relationship between impulsivity/sociability and modes of reinforcement in verbal operant conditioning. Two 2x3 randomized block designs, one each for impulsivity and sociability, were replicated ten times. One hundred and twenty undergraduate female students (60 for impulsivity and 60 for sociability) were individually subjected to Taffel's verbal conditioning procedure. When the conditioning scores of high and low scorers on the impulsivity and sociability scales were compared, it was found that under rewarding conditions ('good' and 'buzzer' in respect of sociability and 'good' in respect of impulsivity) the high scorers' score and under punishing conditions ('electric shock') the low scorers' score was the higher of the two. The study also revealed that the high scorers (on the impulsivity scale) conditioned more under rewarding conditions while the low scorers (both on the impulsivity and sociability scales) conditioned more under punishing ones.

Adolescent↗

PubMed1993

Robustness of some estimators for the analysis of covariance structures.

A sampling experiment was designed to evaluate the robustness of some estimators used in the analysis of covariance structures to misspecification of the discrepancy function in finite samples. The estimators were studied under four distribution (a multivariate normal, an elliptical, a non-elliptically symmetric, and an asymmetric multivariate distribution, and eight sample size (75, 150, 300, 600, 1200, 2400, 4800, 9600) conditions. Parameters of the composite direct product model for a 6-variable MTMM matrix were estimated using the Maximum Wishart Likelihood (MWL), generalized least squares (GLS), asymptotically distribution free (ADF), and approximate ADF (DADF) estimators. Browne's elliptical correction (CMWL) to the test statistic and standard errors for scale-invariant models was also made for each sample. Each of the 32 distribution-sample size conditions was replicated 300 times. The accuracy of the parameter estimates and estimated standard errors and the distribution of the test statistic were studied. The theoretically predicted importance of information contained in higher-order moments of arbitrary distributions was confirmed. Robustness of the MWL and normal theory GLS estimators cannot be taken for granted. Elliptical corrections may be a practical solution to some data analytic problems.

Female↗

PubMed1966

Replication of chloroplast DNA of tobacco.

An experimental method has been designed for determining the relative rates of replication of the chloroplast and nuclear DNA's of Nicotiana tabacum. By this method chloroplast DNA in week-old seedlings is being replicated several times faster than nuclear DNA.

Cell Division↗

PubMed1967

Neoplastic transformation of rat thymic cells induced in vitro by Gross leukemia virus.

Cultures of embryonal rat thymus infected initially with Gross leukemia virus have, at the present time, abundantly replicated infectious virus particles for 20 months. Cells from these cultures, after 3 months in vitro, displayed morphological changes and induced formation of tumors upon isotransplantation. The tumors were serially transplantable, and subsequent transplants continue to carry the initial Gross leukemia virus.

AKR murine leukemia virus↗

PubMed2005

Potent antiviral activity of north-methanocarbathymidine against Kaposi's sarcoma-associated herpesvirus.

Kaposi's sarcoma-associated herpesvirus (KSHV) infection is a prerequisite for the development of Kaposi's sarcoma (KS). Blocking lytic KSHV replication may hinder KS tumorigenesis. Here, we report potent in vitro anti-KSHV activity of 2'-exo-methanocarbathymidine [North-methanocarbathymidine (N-MCT)], a thymidine analog with a pseudosugar ring locked in the northern conformation, which has previously been shown to block the replication of herpes simplex virus types 1 and 2. N-MCT inhibited KSHV virion production in lytically induced KSHV-infected BCBL-1 cells with a substantially lower 50% inhibitory concentration (IC50) than those of cidofovir (CDV) and ganciclovir (GCV) (IC50, mean +/- standard deviation: 0.08 +/- 0.03, 0.42 +/- 0.07, and 0.96 +/- 0.49 microM for N-MCT, CDV, and GCV, respectively). The reduction in KSHV virion production was accompanied by a corresponding decrease in KSHV DNA levels in the N-MCT-treated BCBL-1 cells, indicating that the compound blocked lytic KSHV DNA replication. A time- and dose-dependent accumulation of N-MCT-triphosphate (TP) was demonstrated in lytically induced BCBL-1 cells, while uninfected cells showed virtually no accumulation. The levels of N-MCT-TP were significantly decreased in the presence of 5'-ethynylthymidine, a potent inhibitor of herpesvirus thymidine kinase, resulting in the abrogation of anti-KSHV activity of N-MCT. N-MCT-TP more effectively blocked in vitro DNA synthesis by KSHV DNA polymerase with an IC50 of 6.24 +/- 0.08 microM (mean +/- standard deviation) compared to CDV-diphosphate (14.70 +/-2.47 microM) or GCV-TP (24.59 +/- 5.60 microM). Taken together, N-MCT is a highly potent and target-specific anti-KSHV agent which inhibits lytic KSHV DNA synthesis through its triphosphate metabolite produced in KSHV-infected cells expressing a virally encoded thymidine kinase.

Antiviral Agents↗

PubMed2006

Diversity of basidiomycetes in michigan agricultural soils.

We analyzed the communities of soil basidiomycetes in agroecosystems that differ in tillage history at the Kellogg Biological Station Long-Term Ecological Research site near Battle Creek, Michigan. The approach combined soil DNA extraction through a bead-beating method modified to increase recovery of fungal DNA, PCR amplification with basidiomycete-specific primers, cloning and restriction fragment length polymorphism screening of mixed PCR products, and sequencing of unique clones. Much greater diversity was detected than was anticipated in this habitat on the basis of culture-based methods or surveys of fruiting bodies. With "species" defined as organisms yielding PCR products with > or =99% identity in the 5' 650 bases of the nuclear large-subunit ribosomal DNA, 241 "species" were detected among 409 unique basidiomycete sequences recovered. Almost all major clades of basidiomycetes from basidiomycetous yeasts and other heterobasidiomycetes through polypores and euagarics (gilled mushrooms and relatives) were represented, with a majority from the latter clade. Only 24 of 241 "species" had 99% or greater sequence similarity to named reference sequences in GenBank, and several clades with multiple "species" could not be identified at the genus level by phylogenetic comparisons with named sequences. The total estimated "species" richness for this 11.2-ha site was 367 "species" of basidiomycetes. Since >99% of the study area has not been sampled, the accuracy of our diversity estimate is uncertain. Replication in time and space is required to detect additional diversity and the underlying community structure.

Agriculture↗

PubMed1979

Statistical procedure for evaluating the sensitivity of Limulus amoebocyte lysate by using a reference lysate.

A study was designed to estimate variability of the Limulus amoebocyte lysate test by comparing a reference lysate against itself. Three technicians performed parallel tests, i.e., titrated side by side, the contents of two vials of reference lysate on 4 different days using 24 vials of the United States reference lysate and 12 vials of the United States reference endotoxin. Each parallel test was replicated three times. From the sensitivity endpoints, ratios were calculated for each parallel test. These ratios were converted to the logarithm for estimating variability among technicians and among vials of endotoxin. By using the overall variability of log ratios, a statistical procedure was developed to evaluate the sensitivity of each lot of licensed lysate submitted to the Bureau of Biologics for release.

Endotoxins↗

PubMed1994

Alfalfa yield response to inoculation with recombinant strains of Rhizobium meliloti with an extra copy of dctABD and/or modified nifA expression.

The construction of rhizobial strains which increase plant biomass under controlled conditions has been previously reported. However, there is no evidence that these newly constructed strains increase legume yield under agricultural conditions. This work tested the hypothesis that carefully manipulating expression of additional copies of nifA and dctABD in strains of Rhizobium meliloti would increase alfalfa yield in the field. The rationale for this hypothesis is based on the positive regulatory role that nifA plays in the expression of the nif regulon and the fact that a supply of dicarboxylic acids from the plant is required as a carbon and energy source for nitrogen fixation by the Rhizobium bacteroids in the nodule. These recombinant strains, as well as the wild-type strains from which they were derived, are ideal tools to examine the effects of modifying or increasing the expression of these genes on alfalfa biomass. The experimental design comprised seven recombinant strains, two wild-type strains, and an uninoculated control. Each treatment was replicated eight times and was conducted at four field sites in Wisconsin. Recombinant strain RMBPC-2, which has an additional copy of both nifA and dctABD, increased alfalfa biomass by 12.9% compared with the yield with the wild-type strain RMBPC and 17.9% over that in the uninoculated control plot at the site where soil nitrogen and organic matter content was lowest. These increases were statistically significant at the 5% confidence interval for each of the three harvests made during the growing season. Strain RMBPC-2 did increase alfalfa biomass at the Hancock site; however, no other significant increases or decreases in alfalfa biomass were observed with the seven other recombinant strains at that site. At three sites where this experiment was conducted, either native rhizobial populations or soil nitrogen concentrations were high. At these sites, none of the recombinant strains affected yield. We conclude that RMBPC -2 can increase alfalfa yields under field conditions of nitrogen limitation, low endogenous rhizobial competitors, and sufficient moisture.

Base Sequence↗

PubMed1978

Evidence for the specific association of the chromosomal origin with outer membrane fractions isolated from Escherichia coli.

DNA-envelope complexes isolated from osmotically lysed spheroplasts of Escherichia coli contained 0.2 to 1% of the total cellular DNA after labeling with [3H]thymidine. Molecular weight determinations indicated that the amount of bound DNA was equivalent in most cases to a maximum of three binding sites per chromosome. Bound DNA from E. coli B/r was distributed approximately equally between inner and outer membrane components when envelopes were fractionated on sucrose equilibrium gradients. Outer membrane-DNA complexes, in particular, fraction H1, with a density of 1.24 g/cm3, were quite stable against shearing and against Sarkosyl NL97. In the case of E. coli B/r, H1-DNA was also relatively resistant to deoxyribonuclease. Inner membrane-DNA complexes, in contrast, were quite labile and readily dissociated to release free DNA. The outer membrane fractions did not appear to contain replication fork DNA, but small amounts may have been present in the inner membrane complexes. A two- to eightfold enrichment for chromosomal origin DNA in the envelope was obtained when cultures of E. coli K-12, synchronized for DNA replication, were pulse labeled at different times in the replication cycle. This enrichment was found invariably in the outer membrane fractions. However, the data do not exclude the possibility that this DNA is bound to regions of adhesion between inner and outer membranes which sediment with a density indistinguishable from that of the outer membrane.

Binding Sites↗

PubMed1998

Initiation and velocity of chromosome replication in Escherichia coli B/r and K-12.

The macromolecular composition and a number of parameters affecting chromosome replication were examined over a range of exponential growth rates in two common Escherichia coli strains, B/r and K-12 AB1157. Based on improved measurements of DNA after treatment of exponential cultures with rifampin, the cell mass per chromosomal replication origin (initiation mass) and the time required to replicate the chromosome from origin to terminus (C period) were determined. For these two strains, the initiation mass approached values of 8 x 10(-10) and 10 x 10(-10) units of optical density (at 460 nm) of culture mass per oriC, respectively, at growth rates above 1 doubling/h (at 37 degrees C). The amount of protein per oriC decreased with increasing growth rate for AB1157 and remained nearly constant for the B/r strain. The C period decreased for both strains in an essentially identical manner from about 70 min at 0.6 doublings/h to about 33 min at 3 doublings/h. From the initiation mass and C period, relative or absolute copy numbers for genes with known map locations can be accurately determined at different growth rates. At growth rates above 2 doublings/h, when chromosomes are highly branched, genes near the origin are about threefold more prevalent than genes near the terminus. At a growth rate of 0.6 doubling/h, this ratio is only about 1.7, which reflects the lower degree of chromosome branching.

Chromosomes, Bacterial↗

PubMed2001

Immature monocyte-derived dendritic cells are productively infected with herpes simplex virus type 1.

Herpes simplex viruses (HSV) have developed several immunoevasive strategies. Here we demonstrate a novel mechanism by which HSV type 1 may interfere with the immune response through infection of immature dendritic cells (DC) and selective downmodulation of costimulatory molecules. In our study we show productive infection of immature monocyte-derived DC, which closely resemble sessile Langerhans cells, by sequential expression of immediate-early, early, and late viral proteins and of glycoprotein D mRNA, as well as production of infectious virus of moderate titers. Infection was cytopathic, with the progressive loss of 20 to 45% of cells from 24 to 48 h after infection, with no more than 80% of DC found to be infected. These results are in contrast to those of previous findings of nonpermissive or abortive infection of monocytes and mature monocyte-derived DC. Infection of immature DC also led to selective and asynchronous downregulation of CD1a, CD40, CD54 (ICAM-1) (12 h postinfection), CD80 (24 h postinfection), and CD86 (48 h postinfection) but not of CD11c or major histocompatibility complex class I and II molecules when compared to DC exposed to UV-inactivated virus. Thus, we propose that productive infection of epidermal Langerhans cells in vivo may lead to delayed activation of T cells, allowing more time for replication of HSV type 1 in epidermal cells.

Antigens, CD1↗

PubMed1994

Progressive increases in the methylation status and heterochromatinization of the myoD CpG island during oncogenic transformation.

Alterations in DNA methylation patterns are one of the earliest and most common events in tumorigenesis. Overall levels of genomic methylation often decrease during transformation, but localized regions of increased methylation have been observed in the same tumors. We have examined changes in the methylation status of the muscle determination gene myoD, which contains a CpG island, as a function of oncogenic transformation. This CpG island underwent de novo methylation during immortalization of 10T1/2 cells, and progressively more sites became methylated during the subsequent transformation of the cells to oncogenicity. The greatest increase in methylation occurred in the middle of the CpG island in exon 1 during transformation. Interestingly, no methylation was apparent in the putative promoter of myoD in either the 10T1/2 cell line or its transformed derivative. The large number of sites in the CpG island that became methylated during transformation was correlated with heterochromatinization of myoD as evidenced by a decreased sensitivity to cleavage of DNA in nuclei by MspI. A site in the putative promoter also became insensitive to MspI digestion in nuclei, suggesting that the chromatin structural changes extended beyond the areas of de novo methylation. Unlike Lyonized genes on the inactive X chromosome, whose timing of replication is shifted to late S phase, myoD replicated early in S phase in the transformed cell line. Methylation analysis of myoD in DNAs from several human tumors, which presumably do not express the gene, showed that hypermethylation also frequently occurs during carcinogenesis in vivo. Thus, the progressive increase in methylation of myoD during immortalization and transformation coinciding with a change in chromatin structure, as illustrated by the in vitro tumorigenic model, may represent a common mechanism in carcinogenesis for permanently silencing the expression of genes which can influence cell growth and differentiation.

5-Methylcytosine↗

PubMed1989

Increased pituitary response to somatostatin in aging male rats: relationship to somatostatin receptor number and affinity.

Previous research has established that growth hormone pulse amplitude declines with increasing age. The purpose of this study was to determine whether this decline is associated with (1) increased pituitary response to somatostatin, and/or (2) increased number or affinity of pituitary somatostatin receptors. In the first study, pituitary slices from young (3-4 months), middle-aged (12-14 months), and old (22-24 months) male Fischer 344 rats were superfused with minimal essential medium (1 ml/min) and fractions collected at 5-min intervals. Tissues were stimulated with 10(-7) M hpGRF (1-44) for 1 min and, 40 min later, with hpGRF in the presence of 5 x 10(-9) M somatostatin-14 or somatostatin-28. Two pituitaries from each age group were superfused simultaneously and the experiment replicated 4 times. Growth hormone release was measured by radioimmunoassay. In a second study, somatostatin receptors in purified pituitary membranes from the three age groups were compared using iodo-[Tyr0]-D-Trp8 somatostatin-14. Animals from each age group were pooled, membranes extracted, and incubated with increasing doses of cold peptide. Binding characteristics were analyzed by Scatchard analysis and Ka and Bmax calculated. Results indicated that (1) basal growth hormone release diminished both with age and somatostatin administration, (2) GRF-induced release of growth hormone was similar in all age groups when data were expressed as percent increase from baseline, and (3) in the presence of somatostatin-14, GRF-induced release of growth hormone was attenuated in old as compared to young or middle-aged rats (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1984

Cell proliferation in the principal target organs of the dog (beagle) ovary during various periods of the estrous cycle.

Cell proliferation in the principal target organs of the ovary was studied in 7 beagle dogs during proestrus, early estrus, secretory and regressive metestrus. Pulse labelling with (3H)-thymidine and autoradiography were applied and labelling indices were determined. Organs with squamous and with glandular epithelium except the mammary gland showed a proliferation peak during early proestrus, the incidence of labelling being higher in organs with squamous epithelium. During early proestrus the intensity of labelling decreased in organs with squamous epithelium in the following order: vulva, vagina, portio vaginalis, and portio supravaginalis. At this time cell replication was higher in the superficial glands of the cervix and corpus uteri as well as the circular layer of the myometrium compared with values from the basal glands or the longitudinal layer. The steepest decline of the proliferative activity occurred between the proestrous period. While some labelled cells were observed during secretory metestrus, labelling was almost absent during regressive metestrus. By contrast, the mammary gland began to develop at the periovulatory period and was at the height of its proliferative activity during secretory metestrus. It is concluded for species with a long estrous cycle that: (1) the rate of cell replication in the vulva, vagina, uterus and oviduct is at its peak at the beginning of the estrous cycle and declines during proestrus; (2) as compared to observations in species with short estrous cycles, cell proliferation is very low during metestrus.

Animals↗

PubMed1993

Notes on the dissolution of human dental enamel in dilute acid solutions at high solid/solution ratio.

The aim of the present study was to elucidate the nature of the relationship between enamel apatite and lesion fluid during demineralization. Powdered enamel in samples of 1.0 g was suspended in 3 ml of 10, 30, 50, or 70 mmol/l HCl under gentle agitation for up to 24 h at 20 degrees C. After 20 min and 24 h, pH and the concentrations of calcium and phosphate were determined and the degree of saturation with respect to various calcium phosphates calculated. The experiments were replicated 15 times using the same enamel samples. Twenty minutes after the start of dissolution, both pH and concentrations of calcium and phosphate had increased, and the solution became supersaturated with respect to hydroxyapatite, and in some runs also with respect to brushite. During the subsequent 23 h and 40 min, pH continued to increase, despite the supersaturation with respect to apatite, whilst the concentrations of calcium and phosphate decreased due to formation of apatite and, occasionally, brushite mineral. The data indicated that release of carbonate from enamel and its conversion to H2CO3 caused the increase in pH and thus, played a major role in the dissolution-reprecipitation process.

Calcium↗

PubMedDate not supplied

Guidelines for the design and statistical analysis of experiments in papers submitted to ATLA.

In vitro experiments need to be well designed and correctly analysed if they are to achieve their full potential to replace the use of animals in research. An "experiment" is a procedure for collecting scientific data in order to answer a hypothesis, or to provide material for generating new hypotheses, and differs from a survey because the scientist has control over the treatments that can be applied. Most experiments can be classified into one of a few formal designs, the most common being completely randomised, and randomised block designs. These are quite common with in vitro experiments, which are often replicated in time. Some experiments involve a single independent (treatment) variable, while other "factorial" designs simultaneously vary two or more independent variables, such as drug treatment and cell line. Factorial designs often provide additional information at little extra cost. Experiments need to be carefully planned to avoid bias, be powerful yet simple, provide for a valid statistical analysis and, in some cases, have a wide range of applicability. Virtually all experiments need some sort of statistical analysis in order to take account of biological variation among the experimental subjects. Parametric methods using the t test or analysis of variance are usually more powerful than non-parametric methods, provided the underlying assumptions of normality of the residuals and equal variances are approximately valid. The statistical analyses of data from a completely randomised design, and from a randomised-block design are demonstrated in Appendices 1 and 2, and methods of determining sample size are discussed in Appendix 3. Appendix 4 gives a checklist for authors submitting papers to ATLA.

Animal Testing Alternatives↗

PubMed1988

Inhibition of progesterone secretion from granulosa cells by estradiol and androgens in the domestic hen.

We previously reported no difference in progesterone (P4) secretion from the granulosa layer of the largest follicle (F1) of the domestic hen regardless of the maturity of the F1 follicle. However, coincubation of the granulosa and thecal layers resulted in inhibition of P4 secretion from the less mature F1, but not from the more mature F1. The goal of this study was to determine if estradiol (E2) and androgens secreted by the thecal layer suppress P4 production by the granulosa cells. We removed the granulosa layer from less mature F1 follicles and dispersed granulosa cells (1 x 10(5)) were incubated (3 h) in triplicate with one of these treatments: control, E2, testosterone (T), androstenedione (A), and dihydrotestosterone (DHT; at concentrations of 1 x 10(-7), 1 x 10(-6), and 1 x 10(-5) M), LH (100 ng) as well as LH plus E2, T, A, and DHT at the same concentrations. P4 secretion was measured in the medium and cells, and the experiment was replicated seven times. We found a dose-related suppression of basal and LH-stimulated P4 production by all steroids. In a second experiment (n = 3-5), we tested the specificity of the androgens in suppressing P4 production by granulosa cells by using the aromatase inhibitor 7-(4'-amino)phenylthio-4-androstene-3,17-dione. This compound did not reduce the effectiveness of T in suppressing P4 production. Finally in Exp 3 (n = 4-7), E2 and T were tested individually and in combination at concentrations of 1 X 10(-8)-1 X 10(-5) M. We found a possible synergistic effect, in that the combination of E2 plus T suppressed P4 to a greater degree than either steroid alone. Our results indicate that 1) E2 and androgens suppress basal and LH-stimulated P4 production by granulosa cells in a dose-related manner; 2) androgen suppression of P4 production is not mediated by aromatization to estrogen; and 3) the suppressive effects of E2 and androgens may be synergistic. We conclude that E2 and androgens secreted by the thecal layer may regulate P4 production by the granulosa layer.

Androgens↗