Showing papers by "University of Alberta published in 1987"

Difference in the amplitude of the human soleus H reflex during walking and running.

Abstract: 1. The Hoffman reflex, or H reflex, was strongly modulated in the human soleus muscle during both walking (4 km/h) and running (8 km/h). It was relatively low at the time of heel contact, increased progressively during the stance phase, and reached its maximum amplitude late in the stance phase. During ankle dorsiflexion the H reflex was absent. 2. During running the peak e.m.g. level of the soleus was on average 2.4 times higher than during walking but the maximum amplitude of the H reflex was never larger than during walking. In fact, the H reflex was on average significantly (P less than 0.05 for one-tailed t test) smaller during running than during walking. Furthermore, the slope of the least-squares line fitted to the relation between the H reflex amplitude and the background e.m.g. was always steeper for the walking data than for the running data. 3. The difference in the H reflex in the two tasks is evidence that the size of the H reflex is not simply a passive consequence of the alpha-motoneurone excitation level, as indicated by the e.m.g., but is also influenced by other central neural mechanisms. We suggest that presynaptic inhibition is the most likely mechanism accounting for the change in the slope. 4. The modulation of the reflexes during walking and running can be interpreted in terms of the idea of automatic gain compensation. The decreased gain during running may be appropriate to reduce saturation of motor output and potential instability of the stretch reflex feed-back loop.

Etiology and clinical course of missed spine fractures.

Abstract: A prospective study was designed to document course and outcome. Two hundred fifty-three patients with 274 spinal injuries were reviewed at the time of injury and discharge from hospital, as well as at 1, 2, and 5 years postinjury. Thirty-eight of these patients were identified who had been misdiagnosed at the initial assessment. Fracture location, cause of injury, neurologic deficit, and delay in diagnosis were all documented: 22.9% of cervical injuries, and 4.9% of the thoracolumbar injuries had a delayed diagnosis ranging from less than 1 day to 36 days. The causes of delayed diagnosis were: 1) failure to take X-rays, 2) fractures missed on X-ray, and 3) failure of patients to seek medical attention. Associated factors such as intoxication of the patient, multiple injuries, level of consciousness, or two levels of spinal injury contributed to the delayed diagnosis of these injuries. Certain "at-risk" populations for missed spinal injuries have been identified. In spite of delays in diagnosis, progression of an established neurologic deficit did not appear to occur in our study. However, the development of secondary deficits was significant in the delayed diagnosis group.

The atomic structure of Mengo virus at 3.0 A resolution

Abstract: The structure of Mengo virus, a representative member of the cardio picornaviruses, is substantially different from the structures of rhino- and polioviruses. The structure of Mengo virus was solved with the use of human rhinovirus 14 as an 8 A resolution structural approximation. Phase information was then extended to 3 A resolution by use of the icosahedral symmetry. This procedure gives promise that many other virus structures also can be determined without the use of the isomorphous replacement technique. Although the organization of the major capsid proteins VP1, VP2, and VP3 of Mengo virus is essentially the same as in rhino- and polioviruses, large insertions and deletions, mostly in VP1, radically alter the surface features. In particular, the putative receptor binding "canyon" of human rhinovirus 14 becomes a deep "pit" in Mengo virus because of polypeptide insertions in VP1 that fill part of the canyon. The minor capsid peptide, VP4, is completely internal in Mengo virus, but its association with the other capsid proteins is substantially different from that in rhino- or poliovirus. However, its carboxyl terminus is located at a position similar to that in human rhinovirus 14 and poliovirus, suggesting the same autocatalytic cleavage of VP0 to VP4 and VP2 takes place during assembly in all these picornaviruses.

Epidermal growth factor induces differentiation and secretion of human chorionic gonadotropin and placental lactogen in normal human placenta.

Abstract: Human trophoblast differentiates by the fusion of cytotrophoblasts to form syncytiotrophoblast. To determine factors controlling this process, the effects of epidermal growth factor (EGF) on trophoblast differentiation were studied using long term serum-free culture of isolated trophoblast. Only trophoblast was present in the cultures, as demonstrated by positive immunoperoxidase staining with βhCG, cytokeratin, and trophoblast-specific H315 monoclonal antisera and by the absence of contaminating endothelial cells, fibroblasts, and macrophages, as shown by negative staining with vimentin and OKM1 monoclonal antisera. EGF induced large sustained increases in hCG and human placental lactogen (hPL) secretion in a dose-dependent manner. The minimum effective dose was 0.1 ng/mL, and the maximum effective dose was 1 ng/mL. Light and electron microscopic studies showed EGF-induced differentiation of cytotrophoblast to form syncytiotrophoblast. DNA content and cell number did not change during the process. The fo...

Bacterial resistance to beta-lactam antibiotics: crystal structure of beta-lactamase from Staphylococcus aureus PC1 at 2.5 A resolution.

Abstract: beta-lactamases are enzymes that protect bacteria from the lethal effects of beta-lactam antibiotics, and are therefore of considerable clinical importance. The crystal structure of beta-lactamase from the Gram-positive bacterium Staphylococcus aureus PC1 has been determined at 2.5 angstrom resolution. It reveals a molecule of novel topology, made up of two closely associated domains. The active site is located at the interface between the domains, with the key catalytic residue Ser70 at the amino terminus of a buried helix. Examination of the disposition of the functionally important residues within the active site depression leads to a model for the binding of a substrate and a functional analogy to the serine proteases. The unusual topology of the secondary structure units is relevant to questions concerning the evolutionary relation to the beta-lactam target enzymes of the bacterial cell wall.

A differential scanning calorimetric study of the thermotropic phase behavior of model membranes composed of phosphatidylcholines containing linear saturated fatty acyl chains.

Abstract: The thermotropic phase behavior of a series of 1,2-diacylphosphatidylcholines containing linear saturated acyl chains of 10-22 carbons was studied by differential scanning calorimetry. When fully hydrated and thoroughly equilibrated by prolonged incubation at appropriate low temperatures, all of the compounds studied form an apparently stable subgel phase (the Lc phase). The formation of the stable Lc phase is a complex process which apparently proceeds via a number of metastable intermediates after being nucleated by incubation at appropriate low temperatures. The process of Lc phase formation is subject to considerable hysteresis, and our observations indicate that the kinetic limitations become more severe as the length of the acyl chain increases. The kinetics of Lc phase formation also depend upon whether the acyl chains contain an odd or an even number of carbon atoms. The Lc phase is unstable at higher temperatures and upon heating converts to the so-called liquid-crystalline state (the L alpha phase). The conversion from the stable Lc to the L alpha phase can be a direct, albeit a multistage process, as observed with very short chain phosphatidylcholines, or one or more stable gel states may exist between the Lc and L alpha states. For the longer chain compounds, conversions from one stable gel phase to another become separated on the temperature scale, so that discrete subtransition, pretransition, and gel/liquid-crystalline phase transition events are observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Accounting as a legitimating institution.

Abstract: Recent attempts to reconceptualize the role of accounting in organizations and society have suggested that accounting may be examined as a “legitimating institution”. The concept of legitimation, however, has not developed within a single theoretic tradition, rather it emerges from three sociological traditions, each suggesting a distinct perspective on the phenomena and opening new areas for research. This paper reviews perspectives on legitimation, locates existing research on accounting within them, and suggests some areas for further research.

Are indices of free radical damage related to exercise intensity.

Abstract: The possibility that plasma levels of malonaldehyde (MDA) are altered by exercise has been examined. The presence of MDA has been recognized to reflect peroxidation of lipids resulting from reactions with free radicals. Maximal exercise, eliciting 100% of maximal oxygen consumption ( $$\dot V_{{\text{O}}_{{\text{ 2 max}}} } $$ ) resulted in a 26% increase in plasma MDA (P<0.005). Short periods of intermittent exercise, the intensity of which was varied, indicated a correlation between lactate and MDA (r 2=0.51) (p<0.001). Blood lactate concentrations increased throughout this exercise regimen. A significant decrease (10.3%) in plasma MDA occurred at 40% $$\dot V_{{\text{O}}_{{\text{ 2 max}}} } $$ . At 70% $$\dot V_{{\text{O}}_{{\text{ 2 max}}} } $$ plasma MDA was still below resting values, however the trend to an increase in MDA with exercise intensity was evident. At exhaustion, plasma MDA and lactate were significantly greater than at rest. These results suggest, that exhaustive maximal exercise induces free radical generation while short periods of submaximal exercise (i.e. <70% $$\dot V_{{\text{O}}_{{\text{ 2 max}}} } $$ ) may inhibit it and lipid peroxidation.

The function of authority in transaction cost economics

Abstract: This paper questions the transaction cost characterization of observed authority relations as efficient governance structures. Various inadequacies in the transaction cost account of work organization and the limits of firm size are traced to its neglect of the possibility that authority may be abused opportunistically. This exemplifies a more general propensity in the transaction cost literature: that of explaining economic organization in functionalist terms, with little attention to the causal mechanisms through which efficient governance structures might actually arise. Three such mechanisms are considered, but none is found to provide an adequate rationale for the imputation of efficiency to observed structures.

Average number of nucleotide differences in a sample from a single subpopulation: a test for population subdivision.

Abstract: Unbiased estimates of theta = 4Nmicro in a random mating population can be based on either the number of alleles or the average number of nucleotide differences in a sample. However, if there is population structure and the sample is drawn from a single subpopulation, these two estimates of theta behave differently. The expected number of alleles in a sample is an increasing function of the migration rates, whereas the expected average number of nucleotide differences is shown to be independent of the migration rates and equal to 4N(T)micro for a general model of population structure which includes both the island model and the circular stepping-stone model. This contrast in the behavior of these two estimates of theta is used as the basis of a test for population subdivision. Using a Monte-Carlo simulation developed so that independent samples from a single subpopulation could be obtained quickly, this test is shown to be a useful method to determine if there is population subdivision.

A steroid sex pheromone synchronizes male-female spawning readiness in goldfish

Abstract: Understanding of pheromone function in teleost fish has been impeded by a lack of information on pheromone identities1. Our recent studies2,3 on goldfish Carassius auratus, however, provide strong evidence that 17α,20β-dihydroxy-4-pregnen-3-one (17,20P), the proposed oocyte maturation-inducing steroid hormone in goldfish4 and other teleosts5, could be a potent female sex pheromone. Milt (sperm and seminal fluid) volume in goldfish is increased by exposure to 17,20P (and to a lesser extent by exposure to two precursors of 17,20P, progesterone and 17α-hydroxyprogesterone) but not to other steroids proposed as fish pheromones1,6,7. In addition, the goldfish olfactory epithelium is extremely sensitive to 17,20P (ref. 3), and the increase in milt volume normally induced by 17,20P exposure is abolished by sectioning the medial olfactory tracts, which previously have been implicated in the control of sex behaviour in male goldfish8. We report here that ovulating goldfish release 17,20P into the water and that a rapid (within 15 min) elevation in blood gonadotropin of males mediates the milt response to 17,20P exposure. We conclude that this pheromone system synchronizes milt production with ovulation.

Human motor-unit recruitment during isometric contractions and repeated dynamic movements.

Abstract: Spike-triggered averaging was used to determine the twitch tensions and contraction times of motor units in the abductor pollicis brevis muscle of two human subjects for two directions of isometric contraction: abduction and opposition of the thumb. During isometric contractions in each direction, the threshold force for motor-unit recruitment and the twitch amplitude were correlated linearly. These data suggested that an orderly pattern of recruitment, according to increasing twitch size, describes the function of the human abductor pollicis brevis muscle for each contraction direction. Rank order of motor-unit recruitment in each isometric contraction direction was correlated, but not identical. All units contributed tension in each direction of contraction, so no clear evidence was found for task-dependent motor units. In two subjects, motor-unit recruitment order during isometric contraction of the first dorsal interosseous and abductor pollicis brevis muscles was then compared with that of motor-unit pairs in both muscles during repetitive dynamic movements. Recruitment according to increasing twitch size was largely preserved during the repetitive opening and closing of scissors. The recruitment reversals that were observed were usually between pairs of units with similar thresholds.

Management of injection pain in children.

Abstract: Researchers have come to understand a great deal about pain mechanisms, especially in the past 30 years. This understanding has spawned the development of a number of psychological pain control strategies which have been extensively assessed for use with adults. Less is known about pain control strategies in children. The purpose of this study was to assess the value of 2 cognitive strategies (suggestion and music distraction) in reducing pain in children. Two hundred children, aged 4.5-6.5 years, receiving routine immunization injections were randomly assigned to one of the intervention groups in this factorial study. The groups were designated as: distraction, distraction with suggestion, suggestion and control. Subjects reported their pain using a 4-point pain scale. Distraction was found to significantly decrease pain whereas suggestion did not. Combining suggestion and distraction did not further enhance pain relief compared to use of distraction alone. Age was found to be an important determinant of the success of distraction. Furthermore, age was found to be related to amount of pain reported by children regardless of type of treatment. The results of this study support the use of music distraction in the reduction of injection pain in children.

Saddle dolomite as a by-product of chemical compaction and thermochemical sulfate reduction

Abstract: Petrographic, stable and radiogenic isotope, trace-element, and fluid-inclusion data from the Devonian Nisku reef trend in the subsurface of Alberta, Canada, suggest that saddle dolomite was a by-product of chemical compaction and thermochemical sulfate reduction in subsiding dolomitized rocks. Furthermore, thermochemical sulfate reduction may be representative of other processes that increase the amount of saddle dolomite via an increase in carbonate alkalinity. The data also confirm that saddle dolomite is most likely to form at elevated temperatures from hypersaline brines.

Quaternary stratigraphy of the Fladen area, central North Sea: a multidisciplinary study

Abstract: Based on detailed stratigraphic investigations on a 200.6m long core (BGS borehole No. 81/26) from the Fladen Ground area (British sector), core material from the Sleipner field (Norwegian sector) and shallow seismic profiles between the core-sites, the following conclusions are drawn: (1) The North Sea was glaciated sometime during th elaterpart of Matuyama reversed period. A complete glacial-interglacial-glacial cycle is recorded in these sediments. (2) In a period of marine sedimentation in the Middle Pleistocene, a transgression-regression cycle under boreal-arctic regime is recorded. (3) The Fladen area has subsided between 0.9 and 0.6 m/ka through the later parts of the Quaternary (4) A major glacial event dated at between 130 and 200 ka is recorded as a thick till unit in 81/26. This till, which was deposited by ice moving from the southwest (Scotland), probably represents a period when the Scandinavian and British ice sheets coalesced in the North Sea. (5) Based on the seismic data and the stratigraphy of the Sleipner core, an ice-free, open embayment/dry land is favoured for the central North Sea during the Late Weichselian. (6) From the amino-acid data, it is shown that there has been an episodic style of sedimentation through the Quaternary. (7) of the investigated sediments (which span the last 1 mill. year) ca 98% have been deposited under arctic to boreal-arctic conditions.

The undoing of scenarios.

Abstract: Scenarios with dramatic outcomes often evoke counterfactual thinking, mentally undoing that outcome by mutating events in the causal scenario and thereby allowing for the mental simulation of new outcomes. Is Experiment 1, we manipulated the order of four events in a scenario. Each of these events could be mutated to alter the outcome, and each event was described as having caused the eveni that followed it People preferred to change the first event and showed no preference for changes to the subsequent events. We proposed that perceived mutability of an event is constrained by the existence of prior events that are believed to have caused the event. Experiment 2 examined characteristics of the events themselves, rather than their order, that affect their mutability. When these were framed as a norm, people were relatively unlikely to mutate the event in order to undo the outcome, instead preferring to mutate the exceptions. The norm or exception status of other events in the scenario did not affect the mutability of a focal event. Discussion includes the conditions that naturally trigger counterfactual thinking and the role of counterfactual thinking in affective reactions.

The Psilonichnus Ichnocoenose, and Its Relationship to Adjacent Marine and Nonmarine Ichnocoenoses along the Georgia Coast

Abstract: Along clastic shorelines, the ecological/sedimentological transition from offshore to onshore facies includes a characteristic ecotone between marine and nonmarine facies, typically corresponding to the beach backshore and dunes or to washover fans and supratidal flats. Ichnologically, this quasimarine ecotone yields distinctive mixtures of marine and nonmarine lebensspuren herewith designated the Psilonichnus Ichnocoenose. As exemplified by Holocene and Pleistocene barrier-island sequences in Georgia, this ichnocoenose lies between the marine Skolithos Ichnocoenose, represented by the beach foreshore, and several unnamed nonmarine ichnocoenoses, represented by brackish to freshwater marshes, ponds, creeks, and sloughs, and maritime meadows and forests. In addition to diverse plants and invertebrate lebensspuren in these settings, traces made by amphibians, reptiles, birds, and mammals are potentially diagnostic and preservable. Quaternary sediments and facies tracts along the Georgia coast thus demonstrate (1) the richness of local ichnological and sedimentological detail found in warm-temperate, siliciclastic settings; (2) the distinctive, albeit intergradational character of ichnofacies and lithofacies suites there; (3) the prospects for their preservation in regressive strandplain to strandline stratigraphic sequences; and, therefore (4) their potential analogy with many ancient paralic or epeiric shoreline deposits. LE "PSILONICHNUS ICHNOCOENOSE", ET SON RAPPORT AVEC DES "ICHNOCOENOSE" MARINS ET CONTINENTAUX CONNEXES LE LONG DE LA COTE DE GEORGIE RESUME Le long de rivages clastiques, la transition ecologique/sedimentaire des facies au large des cotes aux facies vers le rivage comprend un "ecotone" caracteristique entre les facies marins et continentaux, typiquement equivalent a la plage, a l'arriere-plage et aux dunes, ou aux deltas interieurs de lagon et aux estrans supratidaux. Ichnologiquement, cet "ecotone" quasi-marin presente des melanges distincts de "lebensspuren" marins et continentaux ici designes "Psilonichnus Ichnocoenose". Comme le demontrent les sequences de cretes d'avant-plage emergies du Holocine et du Pleistocene en Georgie, cet "ichnocoenose" se trouve entre le "Skolithos Ichnocoenose" marin, represente par l'avant-plage, et plusieurs" ichnocoenoses" continentaux sans nom, representes par des marais d'eau douce a saumatre, des etangs, des ruisseaux, et des bourbiers, et des pres et des forets maritimes. En plus des diverses plantes et "lebensspuren" invertebres dans ces milieux, des empreintes laissees par les amphibiens, les reptiles, les oiseaux, et les mammiferes sont potentiellement diagnostiques et peuvent etre preservees. Les sediments et nappes de facies Quaternaires le long de la cote de Georgie demontrent donc (1) la richesse de detail ichnologique et sedimentaire local qu'on trouve dans les milieux detritiques silicieux chauds-temperes, (2) le caractere distinctif quoique graduel des suites d'ichnofacies et de lithofacies, (3) les chances de preservation de ces derniers dans des sequences regressives de plaine littorale jusqu'a l'ancienne ligne de rivage, et donc (4) leur analogie potentielle avec plusieurs ancients depots de ligne de rivage paraliques ou epicontinentaux.