Showing papers by "Dartmouth College published in 1984"

Physiological Functions of Glucocorticoids in Stress and Their Relation to Pharmacological Actions

Abstract: Introduction and Background Modern glucocorticoid endocrinology is a colorful, richly varied, but formless discipline—a profusion of cellular, physiological and pharmacological effects, seemingly unrelated through any central hormonal function. A current list of glucocorticoid effects might include such disparate items as stimulation of hepatic gluconeogenesis, inhibition of glucose uptake by peripheral tissues, suppression of inflammation, enhanced excretion of a water load, induction in various cells of tryptophan oxygenase and glutamine synthetase, suppression of numerous immune reactions, inhibition of secretion of several hormones and neuropeptides, and inhibition of activity of plasminogen activator and other neutral proteinases. Judging from recent writings on glucocorticoid physiology, an item that might be low on the list or missing altogether is “increased resistance to stress”.

Groups in context: A model of task group effectiveness.

Abstract: Deborah L. Gladstein This study tests a comprehensive model of group effectiveness with 100 sales teams in the communications industry. Results indicate that traditional theories of group effectiveness match the implicit theories of team members. These theories account for 90 percent of the variance in team satisfaction and self-reported effectiveness but none of the variance in the teams' sales performance. The findings suggest that theories of group effectiveness need to be revised to include the way in which teams manage interactions across their boundary and the impact of the organizational context.

Random walks and electric networks

Abstract: Probability theory, like much of mathematics, is indebted to physics as a source of problems and intuition for solving these problems. Unfortunately, the level of abstraction of current mathematics often makes it difficult for anyone but an expert to appreciate this fact. Random Walks and Electric Networks looks at the interplay of physics and mathematics in terms of an example — the relation between elementary electric network theory and random walks —where the mathematics involved is at the college level.

User Involvement and MIS Success: A Review of Research

Abstract: User involvement in the design of computer-based information systems is enthusiastically endorsed in the prescriptive literature. However determining when and how much, or even if, user involvement is appropriate are questions that have received inadequate research attention. In this paper research that examines the link between user involvement and indicators of system success is reviewed. The authors find that much of the existing research is poorly grounded in theory and methodologically flawed; as a result, the benefits of user involvement have not been convincingly demonstrated. Until higher quality studies are completed intuition, experience, and unsubstantiated prescriptions will remain the practitioner's best guide to the determination of appropriate levels and types of user involvement; these will generally suggest that user involvement is appropriate for unstructured problems or when user acceptance is important. In order to foster higher quality integrated research and to increase understanding of the user involvement-system success relationship, the authors present the following: a conceptual framework into which previous research has been mapped that can provide direction to future efforts; a review of existing measures of user involvement and system success; a set of variables that have been proposed as potentially impacting the relationship between user involvement and system success.

Job Insecurity: Toward Conceptual Clarity

Abstract: A model is presented that summarizes existing knowledge concerning job insecurity, points at its deficiencies, and identifies further research needed to understand the nature, causes, and consequences of this increasingly important phenomenon. Such knowledge is crucial because job insecurity is a key element in a positive feedback loop that accelerates organizational decline.

The interleukin-2 T-cell system: a new cell growth model.

Abstract: Synchronized interleukin-2 receptor-positive T cells, homogeneous immunoaffinity-purified interleukin-2, and a monoclonal antibody to interleukin-2 receptors were used to show that only three factors are critical for T-cell cycle progression: interleukin-2 concentration, interleukin-2 receptor density, and the duration of the interleukin-2 receptor interaction. Since the proliferative characteristics of T cells are identical to those of both prokaryotic and all other eukaryotic cells, these findings provide a new model that accounts fully for the variables that determine cell cycle progression.

The information system as a competitive weapon

Abstract: Avec l'aide de la technologie d'un systeme d'information, une compagnie peut devenir competitive dans toutes les etapes de ses rapports de consommateur. Le modele de cycle de vie de ressource du consommateur rend cela possible pour de telles compagnies, afin de determiner non seulement quand il existe des opportunites pour des applications strategiques mais aussi que des applications specifiques pourraient etre developpees

Chesapeake bay anoxia: origin, development, and significance.

Abstract: Anoxia occurs annually in deeper waters of the central portion of the Chesapeake Bay and presently extends from Baltimore to the mouth of the Potomac estuary. This condition, which encompasses some 5 billion cubic meters of water and lasts from May to September, is the result of increased stratification of the water column in early spring, with consequent curtailment of reoxygenation of the bottom waters across the halocline, and benthic decay of organic detritus accumulated from plankton blooms of the previous summer and fall. The Chesapeake Bay anoxia appears to have had significant ecological effects on many marine species, including several of economic importance.

How Advertising Affects Sales: Meta-Analysis of Econometric Results:

Abstract: The authors attempt to assess what has been learned from econometric models about the effect of advertising on sales. Short-term and long-term advertising response as well as model fit are analyzed...

Sequencing Rules and Due-Date Assignments in a Job Shop

Abstract: Recent research studies of job shop scheduling have begun to examine the interaction between sequencing priorities and the method of assigning due-dates. This paper surveys the tactical aspects of this interaction, focusing primarily on average tardiness as a measure of scheduling effectiveness. The discussion highlights several factors that can affect the performance of dispatching rules, such as the average flow allowance, the due-date assignment method, and the use of progress milestones. A set of simulation experiments illuminates how these factors interact with the dispatching rule, and the experimental results suggest which combinations are most effective in a scheduling system.

Triggering of the T3-Ti antigen-receptor complex results in clonal T-cell proliferation through an interleukin 2-dependent autocrine pathway

Abstract: Human T-cell clones and anti-T-cell-receptor antibodies (clonotypic) directed at surface receptors for antigen (T3-Ti molecular complex) as well as anti-interleukin 2 (IL-2) and anti-IL-2-receptor antibodies were utilized to investigate the mechanism by which alloantigens or antigen plus self-major histocompatibility complex (MHC) (i.e., physiologic ligand) trigger specific clonal proliferation. Soluble or Sepharose-bound anti-Ti monoclonal antibodies, like physiologic ligand, enhanced proliferative responses to purified IL-2 by inducing a 6-fold increase in surface IL-2 receptor expression. In contrast, only Sepharose-bound anti-Ti or physiologic ligand triggered endogenous clonal IL-2 production and resulted in subsequent proliferation. The latter was blocked by antibodies directed at either the IL-2 receptor or IL-2 itself. These results suggest that induction of IL-2 receptor expression but not IL-2 release occurs in the absence of T3-Ti receptor cross-linking. Perhaps more importantly, the findings demonstrate that antigen-induced proliferation is mediated through an autocrine pathway involving endogenous IL-2 production, release, and subsequent binding to IL-2 receptors.

Collective climate: Agreement as a basis for defining aggregate climates in organizations.

Abstract: Agreement of psychological climate perceptions is proposed as a basis for a composition theory of aggregate climate. Climates based on agreement, termed “collective climates,” are shown to meet sev...

The second impact in catastrophic contact-sports head trauma.

Abstract: CATASTROPHIC brain injury following minor impact has been known to occur in contact sports, particularly football. 1 This peculiar susceptibility remains unexplained. However, the common resumption of contact play soon after concussion suggests that sequential minor impacts may occasionally lead to major cerebral pathological conditions. If these injuries have a compounding effect rather than representing isolated events, then additional impact to an already compliance-compromised brain might precipitate a catastrophic increase in intracranial pressure, perhaps through loss of vasomotor tone. We report a case documenting a preexisting cerebral contusion and the lethal effect of a second minor impact. This case suggests that clinical examination alone may sometimes be inadequate in evaluating persisting symptoms after minor head injury. In the athlete who has had a cerebral concussion, computed tomographic (CT) scanning may be required before medical clearance to resume play is justified. Report of a Case A 19-year-old, right-handed, college football player

Multiple indicators: Internal consistency or no necessary relationship?

Abstract: The preceding discussion demonstrates the importance of having an explicit measurement model before analyzing measures. It is not valid to make any blanket statement on whether or not indicators should correlate until we know what type of indicators they are. If they are effect-indicators that have “well-behaved” errors and are positive measures of a single latent variable, then the internal-consistency view is appropriate and positive correlations of the indicators should occur. If cause-indicators are used then the NNR view is correct; indicator intercorrelations may be positive, negative, or zero. Finally, in general MIMIC models, cause-indicators have NNR while effect-indicators should be positively related under the assumptions of the model. In general, a cause- or an effect-indicator may have any type of relation. Given the dominance of the internal-consistency perspective these simple results have serious implications. The empirical practice of factor-analyzing items to determine which measures “hang together” makes little sense if some of the indicators are cause-indicators. Similarly, computing “item-total” (cf. Nunnally, 1978, pp. 279–287) correlations as a means to select items for an index is not valid if cause-indicators are present. It seems quite possible that a number of items (or indicators) have not been used in research because of their low or negative correlation with other indicators designed to measure the same concept. If some of these are cause-indicators, researchers may have unknowingly removed valid measures. On the other hand, these findings are not an excuse to include any indicators of interest in a measure. Ideally, the researcher should decide in advance which are effect- and which are cause-indicators. On the basis of the assumed measurement model, the expected associations may be predicted and tested. In sum, the advice of Blalock seems particularly appropriate: “One should be especially on guard against procedures that supposedly permit one to appraise the ‘validity’ of an indicator on the basis of magnitudes of correlation coefficients, without the benefit of a specific theoretical model” (Namboodiri et al., 1975, p. 600).

Characterization of DNA structures by laser Raman spectroscopy.

Abstract: Oriented fibers drawn from aqueous gels of calf-thymus DNA were maintained at constant relative humidites of 75 and 92% to yield canonical A-DNA and B-DNA structures, respectively. Raman spectra of the two forms of DNA were recorded over the spectral range 300–4000 cm−1. The authenticated DNA fibers were deuterated in hygrostatic cells containing D2O at appropriate relative humidities, and the corresponding spectra of deuterated DNAs were also obtained. The spectra reveal all of the Raman scattering frequencies and intensities characteristic of A- and B-DNA structures in both nondeuterated and deuterated froms, as well as the frequencies and intensities of adsorbed solvent molecules from which the hydration content of DNA fibers can be calculated. Numerous conformation-sensitive vibrational modes of DNA bases and phosphate groups have been identified throughout the 300–1700-cm−1 interval. Evidence has also been obtained for conformation sensitivity of deoxyribosyl CH stretching modes in the 2800–3000-cm−1 region. Raman lines of both the backbone and the bases are proposed as convenient indicators of A- and B-DNA structures. The results are extended to Z-DNA models investigated previously. Some implications of these findings for the determination of DNA or RNA structure from Raman spectra of nucleoproteins and viruses are considered.

Effects of plant species and foliage structure on the foraging behavior of forest birds

Abstract: On etudie le comportement alimentaire de Vireo olivaceus, Setophaga ruticilla, V. philadelphicus, Dendroica caerulescens en fonction des types de plantes et des diverses strates de la foret (New Hampshire)

Applications of the Proper Forcing Axiom

Abstract: Publisher Summary The chapter presents a more powerful version of Martin Axiom (MA), the Proper Forcing Axiom (PFA) that is successful at settling problems left open by MA PFA is obtained from MA by replacing the countable chain condition by properness In addition to the countable chain condition (ccc) partial orderings, the proper partial orderings include the countably closed and Axiom A orderings and many others as well Like the ccc orderings, the proper orderings are closed under forcing composition Thus, PFA applies to many more orderings than MA, and this is one source of its power Another source of power is the fact that large cardinals are needed to obtain the consistency of PFA This means that PFA can be applied to problems that MA has no hope of solving simply because of questions of consistency strength

Senile systemic amyloidosis.

Abstract: Senile systemic amyloid contains the prealbumin-like fibril protein, ASc1, and is the only known form of systemic age-related amyloid. Although it involves predominantly the heart, it may be found in a wide range of tissues. Immunologic studies show that ASc1 cross reacts with human prealbumin (PA) in binding reactions but not in immunoprecipitation reactions. Protein ASc1 shows complete homology with PA in four residues isolated. However, unlike PA, Asc1 may have a blocked N-terminus and is composed of at least three components. Anti-ASc1 forms a line of precipitation with sera from patients with familial amyloidosis. A similar weak reaction has been observed in some elderly patients with senile systemic amyloid.

Shock-induced analgesia on the formalin test: effects of shock severity, naloxone, hypophysectomy, and associative variables.

Abstract: Rats were exposed to three shocks, spaced 20 s apart, at two different levels of severity, low (.75 s, 1 mA) and high (3 s, 4 mA). Both shock levels produced a similar suppression of the recuperative behavior elicited by an injection of formalin into a rat's hind paw. Naloxone fully reversed the analgesia produced by the low-severity shock but only partially reversed the analgesia produced by the high-severity shock (Experiment 1). Hypophysectomy did not alter the level of analgesia (Experiment 2). When the rats were tested in a chamber different from the one they were shocked in, both analgesias were totally reversed (Experiment 3). However, imposing a delay between shock and analgesia testing did not reduce analgesia (Experiment 4). These results suggest that analgesia is not directly elicited by the shock but by apparatus stimuli associated with shock. Further support for this position was obtained when it was found that a Pavlovian extinction procedure could completely eliminate analgesia (Experiment 5). In all of the experiments, the freezing response, one of the rat's species-specific defense reactions, was monitored simultaneously with recuperative behavior. A parallel was found between analgesia and this defensive response, a result suggesting that an animal's endogenous analgesic systems may be activated along with the animal's defensive motivational system. The results point to the critical nature of associative variables in the control of endogenous analgesic systems. They also suggest that shock severity is a determinant of analgesia's sensitivity to naloxone.

The Functions of Acetylcholine in the Rabbit Retina

Abstract: Rabbit retinas were incubated in vitro under conditions known to maintain their physiological function. The acetylcholine stores of the cholinergic amacrine cells were labelled by incubation in the presence of [3H]choline. The tissue was then mounted in a fast-flow superfusion chamber, and the release of [3H]acetylcholine under various conditions was measured by liquid cation exchange or high-voltage electrophoresis. When the retina was stimulated by flashing light, the rate of appearance of radioactive acetylcholine in the superfusate increased, with a latency shorter than the resolution of the system. The rate of release of acetylcholine remained elevated as long as the light was flashing, and returned rapidly to baseline when the light was extinguished. A one minute stimulation with steady light caused a burst of acetylcholine release following stimulus onset and a second, smaller, burst following stimulus cessation. In the presence of 2-amino-4-phosphonobutyrate (APB), an agent known to eliminate selectively the transmission of ON responses to the proximal retina, steady light caused acetylcholine release only at stimulus cessation. Other retinas were labelled with [3H]choline, then incubated for 10-80 min in the presence of flashing light (to promote acetylcholine release) and either control medium or medium containing 100 micron APB (to prevent release from cells activated by stimulus onset). These retinas were quick-frozen, freeze-dried and radioautographed on dry emulsion. In retinas incubated under control conditions [3H]acetylcholine was initially present within two bands within the inner plexiform layer. The two bands became fainter together as the tissue's [3H]acetylcholine was released. APB selectively retarded the depletion of [3H]acetylcholine from the band nearest the ganglion cell layer. We conclude that the displaced cholinergic amacrine cells release acetylcholine at the transient when light appears, and the conventionally placed cholinergic amacrine cells release acetylcholine at the transient when light is extinguished. The retinal ganglion cells that receive a light-driven cholinergic input are distinguished from those that do not by a great sensitivity to slow stimulus motion. It is proposed that the dense plexus of cholinergic dendrites and the transient nature of acetylcholine release combine to create the local subunit that enables detection of motion within regions smaller than those ganglion cells' receptive fields.

Acetylcholine-synthesizing amacrine cells: identification and selective staining by using radioautography and fluorescent markers.

Abstract: The fluorescent DNA stain 4,6,diamidino-2-phenylindole (DAPI) was applied to the cut axons of the rabbit optic tract, from which it was retrogradely transported to the retinal ganglion cell bodies. The labelled retinas were isolated from the eye and maintained in vitro in the presence of [3H]choline. They were then quick-frozen, freeze-dried, vacuum-embedded, and radioautographed on dry emulsion for identification of the acetylcholine-synthesizing cells. Inspection of the radioautographs by fluorescence microscopy showed the two labels not to co-exist: the cells that contained the transported fluorescence did not contain radioactive acetylcholine. In other animals the optic nerve was sectioned, causing retrograde degeneration of a large fraction of the ganglion cells. A population of small, round neurons in the ganglion cell layer was spared. These retinas synthesized [3H]acetylcholine at the same rate as control tissues; and radioautography showed an identical distribution of the acetylcholine-synthesizing cells. We conclude that the acetylcholine-synthesizing neurons of the ganglion cell layer are displaced amacrine cells. When DAPI was injected intraocularly instead of being applied to the optic tract, a regular mosaic of neurons in the ganglion cell layer was selectively stained, and two bands of fluorescence were observed in the inner plexiform layer, at the level where two bands of radioactive acetylcholine were observed in radioautographs. Quantitative analysis showed that the DAPI-stained cells were the same size as those that survive optic nerve section. Like the acetylcholine-synthesizing cells, they appear to be displaced amacrines; when wheatgerm agglutinin labelled by Evans blue was applied to the optic tract and DAPI was injected intraocularly, the red fluorescence of Evans blue and the blue fluorescence of DAPI accumulated in different cells. When DAPI was injected intraocularly and radioautography for acetylcholine was carried out, the cells brightly labelled by DAPI were found to have synthesized acetylcholine. We conclude that topically applied DAPI selectively labels the acetylcholine-synthesizing neurons of the ganglion cell layer. The distribution of the acetylcholine-synthesizing cells was established by counting the DAPI-labelled cells in whole-mounts.(ABSTRACT TRUNCATED AT 400 WORDS)

Spine development in the rotifer Keratella cochlearis: induction by cyclopoid copepods and Asplanchna

Abstract: SUMMARY. 1. Spine development in a clone of unspined Keratella cochlearis was promoted by a water soluble factor released by the copepods Tropocyclops prasinus and Mesocyclops edax and by the predatory rotifer Asplanchna priodonta. Between 9 and 55% of K. cochlearis populations cultured in predator-conditioned media responded to the inducing chemical. 2. The K. cochlearis form possessing a posterior spine of medium length was much less susceptible to predation by small Tropocylops and Asplanchna than the form lacking the posterior spine. These predators consistently selected the unspined form over the spined form when offered equal densities of each. However, both spined and unspined forms were equally susceptible to predation by large Mesocyclops. 3. The phenotypic variation of offspring produced from induced unspined Keratella females encompassed much of the variation reported for the taxon in North America. These morphotypes are similar to the variation of forms reported for the K. cochlearis tecta series known from Europe. We suggest that the North American morphotypes be identified in studies of this species because the presence of the posterior spine can greatly affect predator selectivity.

A comparative study of the enzymatic hydrolysis of acid-pretreated white pine and mixed hardwood

Abstract: Removal of hemicellulose by acid pretreatment in a flow reactor followed by enzymatic hydrolysis of the neutralized slurry has resulted in glucose yields as high as 95% for mixed hardwood. For white pine, however, the maximum glucose yield is 65%. Although pine has a higher extractives content, removal of the extractives prior to enzymatic hydrolysis does not increases the glucose yield. Pore size measurements reveal that the increase in pore volume, in the size range of the cellulase molecule, following pretreatment for pine is only about one-half the value obtained with mixed hardwood. This suggests that pore volume is an important determinant of substrate-enzyme reactivity.

Localized Hyperthermia in the Treatment of Malignant Brain Tumors Using an Interstitial Microwave Antenna Array

Abstract: An interstitial microwave antenna array hyperthermia (IMAAH) system was evaluated in a series of acute experiments for its ability to generate localized hyperthermic fields in the normal adult and developing dog brain. Using a single microwave antenna, the maximum diameter of heating greater than or equal to 42°C was 1.3 cm. Using four microwave antennas, temperatures greater than or equal to 42°C were obtained over a 2.5 cm cross-sectional diameter. Normal gray matter cannot be heated above 42.2°C for 60 min without causing acute damage to cortical neurons. Edema formation can occur at temperatures as low as 42°C in both gray and white matter. Disruption of myelin tracts in white matter is apparent at temperatures of 43.0-43.5°C. The IMAAH system generates significantly higher and more variable temperature distributions in virally induced experimental brain tumors than in the developing dog brain at the same power levels.