Showing papers by "Dalhousie University published in 1988"

Two-Point Step Size Gradient Methods

Abstract: Etude de nouvelles methodes de descente suivant le gradient pour la solution approchee du probleme de minimisation sans contrainte. Analyse de la convergence

Inhibitory tagging system facilitates visual search.

Abstract: Two visuospatial phenomena, serial search and inhibition of return, have recently gained the attention of scientists from such diverse disciplines as neuroscience, artificial intelligence and cognitive psychology1–5. A linear increase in search latency with increasing display size has been assumed to reflect serial focused attention to each item in the display. A delay in the detection of a signal in a previously attended location has been assumed to reflect an inhibitory process that may be used to prevent attention from returning to the same stimulus. The following study of human performance supports these assumptions and, by demonstrating that inhibition of return operates in serial search, presumably to improve search efficiency, provides a functional link between these two phenomena.

Heat-shock response is associated with enhanced postischemic ventricular recovery.

Abstract: In cells, hyperthermia induces synthesis of heat-shock proteins and the acquisition of thermotolerance. Thermotolerant cells are resistant to subsequent oxidative stress. In this study, heat-shocked hearts were examined for evidence of protection during ischemia and reperfusion. Rats were exposed to 15 minutes of 42 degrees C hyperthermia. Twenty-four hours later their hearts were isolated and perfused and the contractility examined during and after ischemic perfusion. No protection was observed during ischemic perfusion. However, upon reperfusion heat-shocked hearts had recovery of contractility within 5 minutes of reperfusion, while control hearts showed no contractility at this time. Throughout 30 minutes of reperfusion heat-shocked hearts had significantly improved recovery of contractile force, rate of contraction and rate of relaxation. Creatine kinase release, associated with reperfusion injury, was significantly reduced from a high of 386.8 +/- 78.9 mU/min/g heart wt for controls to 123.7 +/- 82.9 mU/min/g heart wt for heat-shocked hearts at 5 minutes of reperfusion. Following 30 minutes of reperfusion, ultrastructural examination revealed less damage of mitochondrial membranes in the heat-shocked hearts. Further biochemical investigations revealed that the antioxidative enzyme, catalase, was significantly increased to 137 +/- 12.7 U/mg protein in the heat-shocked hearts while the control value was 64.8 +/- 8.3 U/mg protein. Hyperthermic treatment, which induces the heat-shock response, may be therapeutic for salvaging ischemic myocardium during reperfusion, through a mechanism involving increased levels of myocardial catalase.

First report of a Canadian epidemiological study of autistic syndromes.

Abstract: This report describes an epidemiological investigation of the autistic syndrome using new research diagnostic criteria (Denckla, 1986). The focus here is on the methods of screening and follow-up, and on a description of the cases identified within a circumscribed region of Nova Scotia. Autism, as defined by social deviance, language impairment and repetitive or ritualistic behaviours, has a prevalence of 10 per 10,000 and a male to female ratio of 2.5 : 1. These findings are discussed relative to those reported previously.

Ocean primary production and available light: further algorithms for remote sensing

Abstract: In the context of remote sensing of the ocean, the general problem of estimating water column production from surface irradiance and column chlorophyll concentration is examined, and some refinements are made to the linear theory presented by Platt (1986, Deep-Sea Research , 33 , 149–163). Further empirical evidence is presented to show the stability of the relationship between surface light and biomass-normalized primary production of the ocean water column. A theoretical explanation is given for the non-zero intercept often obtained when these two variables are regressed. The systematic errors in the estimation of primary production by remote sensing, due to non-uniformity in the biomass profile, are examined through sensitivity analyses on a generalized biomass profile. The errors are shown to be functions of the parameters of the biomass profile, of the photosynthetic parameters and of the optical properties of the water. The probable random errors in the estimation of water column primary production using remotely sensed data are evaluated. Some general issues related to the collection and assimilation of data on ocean primary production are addressed.

Amiloride enhances postischemic ventricular recovery: possible role of Na+-H+ exchange

Abstract: Amiloride (40 micrograms/ml) was studied in the isolated rat heart subjected to low-flow ischemia followed by reperfusion. Reperfusion after 30 min of ischemia produced recoveries of force, rate of force development (+dF/dt), and rate of relaxation (-dF/dt) of 42, 82, and 71%, respectively, in control hearts. Amiloride did not enhance the maximum degree of recovery, although, when present during ischemia, it markedly shortened the time required for peak recovery. Reperfusion after 60 min of ischemia resulted in 18, 43, and 34% recovery of force, +dF/dt, and -dF/dt, respectively. Amiloride significantly enhanced recovery to a maximum of 39, 88, and 78% for force, +dF/dt, and -dF/dt, respectively. The improved contractile recovery was accompanied with substantial reductions in the release of creatine kinase (CK) and 6-ketoprostaglandin F1 alpha. Coronary perfusion pressure and resting tension were generally unaffected by amiloride, although there was a moderate tendency to attenuate these parameters after reperfusion. The salutary effects of amiloride were dependent on the drug's presence during ischemia with maximum protection when it was administered during both ischemia and reperfusion and no benefit when added at the time of reperfusion. Because of amiloride's well-documented property in inhibiting Na+-H+ exchange, it is possible that this process plays an important role in modulating the cardiac response to reperfusion.

The effects of unilateral brain damage on visually guided reaching: hemispheric differences in the nature of the deficit.

Abstract: Groups of patients suffering from unilateral damage to the left or right cerebral hemisphere were compared to a group of age-matched normal controls in a visually guided pointing task. Subjects were required to reach quickly and accurately to small visual targets as soon as they appeared on the screen in front of them. All reaches, which were quite unrestricted, were videotaped by rotary-shutter cameras and analyzed by a computer-assisted system which allowed analysis of the kinematic parameters of the movement in three-dimensional space. The groups were compared on the basis of their latency to initiate a reaching movement, the accuracy with which they achieved the target's position, and various measures derived from the instantaneous velocity of the movement. Both patient groups were found to be less accurate than controls and to require more time after the target was illuminated to complete the reach. But while the right-hemisphere group took longer to initiate a reach, the kinematic parameters of the movements they produced did not differ from those of the control group. In contrast, the left-hemisphere group did not differ from the control group in the time required to initiate a reaching movement but did require a greater period of time to execute the reach once it had been initiated. It is suggested that the right hemisphere group were deficient in the speed with which they could determine the spatial position of the target, while the left hemisphere group were deficient in their ability to select an appropriate motor program to achieve the target position and/or to monitor the movement and update the motor program as it was being executed.

Exposure to Parturient Cats: A Risk Factor for Acquisition of Q Fever in Maritime Canada

Abstract: Over a 34-mo period we studied 51 patients with Q fever and 102 control subjects (with various lower-respiratory-tract infections) who were matched for age, sex, and time of onset of infection. By univariate analysis (not adjusted for multiple comparisons), cases differed significantly from controls in the following activities: working on a farm; slaughtering or dressing animals; and contact with cats, cattle, and sheep. The strongest association was with exposure to stillborn kittens--11 of 51 cases vs. none of 102 controls (P less than .00000)--and with exposure to parturient cats (odds ratio, 10.3; 95% confidence interval, 3.5-31.8). Exposures to newborn animals (chiefly kittens) and stillborn kittens were significant risk factors by multivariate analysis, as were rural residence and slaughtering or dressing animals. In 13 Q fever incidents following exposure to parturient cats, 80 people became ill, 52 of whom had serological evidence of recent Coxiella burnetii infection (most of the others were not tested).

Long-term enhancement of evoked potentials in cat somatosensory cortex produced by co-activation of the basal forebrain and cutaneous receptors.

Abstract: Averaged evoked potentials from primary somatosensory cortex (SEPs) were recorded before and after pairing the peripheral stimuli with electrical activation of the basal forebrain (BF) in anesthetized cats. Four pulses at 400 Hz were delivered to the BF 120 ms before each cutaneous stimulus and 10 to 660 such pairings were found to produce an enlargement of the SEP in 10 of 11 animals. The average increase in amplitude of the initial peak of the SEP was 69%. The SEP remained enhanced in five of six animals that were tested an hour or more after the pairing, and in one case the SEP was tested 4.5 h after pairing without diminution. The effective BF sites were located in the substantia innominata and at the rostral pole of the globus pallidus, regions known to contain many cholinergic cell bodies. Enhancement occurred consistently only if stimulation of the BF site elicited a positive wave in the cortex at a latency of 11 to 18 ms. Repeated BF stimulation without cutaneous input did not produce a change in subsequent SEPs. The long-term changes described here may be involved in experimentally- and naturally-induced cortical reorganization.

Multiple genetic mechanisms for the evolution of senescence in Drosophila melanogaster

Abstract: We present the results of selection experiments designed to distinguish between antag- onistic pleiotropy and mutation accumulation, two mechanisms for the evolution of senescence. Reverse selection for early-life fitness was applied to laboratory populations of Drosophila mela- nogaster that had been previously selected for late-life fitness. These populations also exhibited reduced early-age female fecundity and increased resistance to the stresses of starvation, desiccation, and ethanol, when compared to control populations. Reverse selection was carried out at both uncontrolled, higher larval rearing density and at controlled, lower larval density. In the uncon- trolled-density selection lines, early-age female fecundity increased to control-population levels in response to the reintroduction of selection for early-age fitness. Concomitantly, resistance to star- vation declined in agreement with previous observations of a negative genetic correlation between these two characters and in accordance with the antagonistic-pleiotropy mechanism. However, resistance to stresses of desiccation and ethanol did not decline in the uncontrolled-density lines during 22 generations of reverse selection for early-life fitness. The latter results provide evidence that mutation accumulation has also played a role in the evolution of senescence in this set of Drosophila populations. No significant response in early-age fecundity or starvation resistance was observed in the controlled-density reverse-selection lines, supporting previous observations that selection on Drosophila life-history characters is critically sensitive to larval rearing density.

The morphology and tectonics of the Mark area from Sea Beam and Sea MARC I observations (Mid-Atlantic Ridge 23° N)

Abstract: High-resolution Sea Beam bathymetry and Sea MARC I side scan sonar data have been obtained in the MARK area, a 100-km-long portion of the Mid-Atlantic Ridge rift valley south of the Kane Fracture Zone. These data reveal a surprisingly complex rift valley structure that is composed of two distinct spreading cells which overlap to create a small, zero-offset transform or discordant zone. The northern spreading cell consists of a magmatically robust, active ridge segment 40–50 km in length that extends from the eastern Kane ridge-transform intersection south to about 23°12′ N. The rift valley in this area is dominated by a large constructional volcanic ridge that creates 200–500 m of relief and is associated with high-temperature hydrothermal activity. The southern spreading cell is characterized by a NNE-trending band of small (50–200 m high), conical volcanos that are built upon relatively old, fissured and sediment-covered lavas, and which in some cases are themselves fissured and faulted. This cell appears to be in a predominantly extensional phase with only small, isolated eruptions. These two spreading cells overlap in an anomalous zone between 23°05′ N and 23°17′ N that lacks a well-developed rift valley or neovolcanic zone, and may represent a slow-spreading ridge analogue to the overlapping spreading centers found at the East Pacific Rise. Despite the complexity of the MARK area, volcanic and tectonic activity appears to be confined to the 10–17 km wide rift valley floor. Block faulting along near-vertical, small-offset normal faults, accompanied by minor amounts of back-tilting (generally less than 5°), begins within a few km of the ridge axis and is largely completed by the time the crust is transported up into the rift valley walls. Features that appear to be constructional volcanic ridges formed in the median valley are preserved largely intact in the rift mountains. Mass-wasting and gullying of scarp faces, and sedimentation which buries low-relief seafloor features, are the major geological processes occurring outside of the rift valley. The morphological and structural heterogeneity within the MARK rift valley and in the flanking rift mountains documented in this study are largely the product of two spreading cells that evolve independently to the interplay between extensional tectonism and episodic variations in magma production rates.

The evolutionary relationships among known life forms.

Abstract: Sequences of small subunit (SSU) and large subunit (LSU) ribosomal RNA genes from archaebacteria, eubacteria, and the nucleus, chloroplasts, and mitochondria of eukaryotes have been compared in order to identify the most conservative positions. Aligned sets of these positions for both SSU and LSU rRNA have been used to generate tree diagrams relating the source organisms/organelles. Branching patterns were evaluated using the statistical bootstrapping technique. The resulting SSU and LSU trees are remarkably congruent and show a high degree of similarity with those based on alternative data sets and/or generated by different techniques. In addition to providing insights into the evolution of prokaryotic and eukaryotic (nuclear) lineages, the analysis reported here provides, for the first time, an extensive phylogeny of the mitochondrial lineage.

Intracortical connections and their physiological correlates in the primary auditory cortex (AI) of the cat

Abstract: We studied the functional and anatomical properties of the intrinsic connections in the primary auditory cortex (AI) of the cat by using physiological mapping and retrograde tracing methods. Our results revealed that a focal microinjection of tracer labeled as many as five intracortical patches in AI. The patches contained labeled pyramidal and non-pyramidal cell types, most of which were clustered in the middle layers. A densely distributed anterograde-like reaction product was present in the superficial layers above the labeled cells. The distribution of the patches was anisotropic, with most patches occurring dorsal, ventral, and anterior to the injection site. We examined the correlation between the characteristic frequency (CF) and binaural response properties of the injected and labeled regions. We found local labeling in regions possessing CFs equivalent to or slightly greater than that of the injected area. This appears to be a specific connection since we were able to predict the general location of many of the patches on the basis of the organization of the isofrequency domains. Patches were more numerous dorsoposterior to the injection site when the isofrequency contours ran obliquely (i.e., dorsoposterior to ventroanterior) across AI. The binaural response properties of the injected and labelled regions, however, were unrelated.

Lymphocyte recruitment in delayed-type hypersensitivity. The role of IFN-gamma.

Abstract: Lymphocytes are recruited out of the blood into delayed-type hypersensitivity (DTH) reactions, but the factors controlling their migration are poorly understood Our previous studies have shown that IFN-alpha/beta, its inducers, and T cell lymphokines can induce lymphocyte migration into the skin after intradermal injection The present studies were designed to determine the effect of rIFN-gamma, IL-1, and anti-IFN-gamma on lymphocyte recruitment into DTH Small peritoneal exudate lymphocytes, which preferentially migrate to inflammatory sites, were labelled with 111In and injected iv into rats The intradermal injection of IFN-gamma stimulated the migration of these lymphocytes into the skin IL-1 induced very little migration by itself, but enhanced the effect of IFN-gamma Kinetic analysis demonstrated that the migration of lymphocytes to IFN-gamma was rapid, with a peak at 6 h, whereas migration into a DTH reaction was minimal for the first 8 h and reached a peak 24 h after intradermal injection Polyclonal rabbit anti-IFN-gamma anti-serum, and a Mab to IFN-gamma, DB-2, could almost completely block lymphocyte migration induced by IFN-gamma Furthermore, DB-2 inhibited lymphocyte recruitment into DTH reactions by 50 to 90% This Mab did not affect migration in response to IFN-alpha/beta, although it partially inhibited the response to polyI:C The effect of IFN-gamma on lymphocyte recruitment was not specific for small peritoneal exudate lymphocytes, because both spleen T cells and lymph node cells migrated in response to IFN-gamma and DB-2 inhibited the recruitment of splenic T cells to DTH Thus, IFN-gamma is a potent stimulator of lymphocyte migration into the skin and a major mediator of lymphocyte recruitment into DTH

Heat waves, baby booms, and the destruction of kelp beds by sea urchins

Abstract: Large populations of sea urchins, Strongylocentrotus droebachiensis (Muller), destroyed kelp beds along the Atlantic coast of Nova Scotia in the 1960's and 1970's. The origin of these large sea urchin populations is not understood. We have investigated the potential influence of variable growth and development of the planktonic larvae of sea urchins (in response to temperature and food abundance) on recruitment of benthic juveniles. The adult sea urchins were collected at Sandy Cove, Digby County, Nova Scotia, Canada, in December 1986. Temperature strongly affected larval size and the growth of the echinus rudiment within the range 3° to 9°C, and larvae grew most rapidly at 14°C. Food abundance had a smaller effect on larval growth, and these effects were apparent only at high temperature. Larvae fed the same concentration of two different algal food species grew and developed similarly. Correspondence between spring temperature variation and qualitative variation in sea urchin recruitment, as well as strong temperature effects on larval growth in culture, and the occurrence of a large, positive temperature anomaly in June 1960, all suggest that temperature effects on larval growth and development may have led to intense sea urchin recruitment in 1960 and the appearance of large adult populations 4 to 6 yr later. This result invites further research.

Topical anesthesia of the skin by liposome-encapsulated tetracaine.

Abstract: The potential of a liposomal local anesthetic formulation to provide topical anesthesia of the intact skin was investigated Tetracaine base 05% was encapsulated into multilamellar phospholipid vesicles The topical anesthetic effects of the liposomal and a control (Pontocaine cream) preparation were evaluated by pinprick technique in adult volunteers Liposomal tetracaine-produced anesthesia, which lasted at least 4 hours after 1 hour application under occlusion Pontocaine cream was ineffective The liposomal formulation appeared to be suitable to provide long lasting anesthesia of the skin with low drug concentration

Omnivorous feeding behavior of the antarctic krill Euphausia superba

Abstract: Feeding experiments were conducted at Palmer Station from December 1985 to February 1986 to examine the potential role of copepod prey as an alternative food source for Euphausia superba. Copepod concentration, copepod size, phytoplankton concentration, the duration of krill starvation and the volume of experimental vessels were altered to determine effects on ingestion and clearance rates. Krill allowed to feed on phytoplankton and copepods in 50-litre tubs showed greatly increased feeding rates relative to animals feeding in the much smaller volumes of water traditionally used for krill-feeding studies. Clearance rates on copepods remained constant over the range of concentrations offered, but clearance rates on phytoplankton increased linearly with phytoplankton concentration. Feeding rates increased when larger copepods were offered and when krill were starved for two weeks prior to experiments. Clearance rates of krill feeding on copepods were higher than, but not correlated with, their clearance rates on phytoplankton in the same vessel. E. superba may have a distinct mechanism for capturing copepods, perhaps through mechanoreception. Although our observed clearance rate of 1055 ml krill-1 h-1 indicates that krill can feed very efficiently on copepod prey, such feeding would meet less than 10% of their minimum metabolic requirements at the “typical” copepod concentrations reported for Antarctic waters. However, substantial energy could be gained if krill fed on the patches of high copepod concentrations occasionally reported during the austral summer, or if krill and copepods were concentrated beneath the sea ice during the winter or spring months. Our results, indicating efficient feeding on zooplankton and higher clearance rates on phytoplankton than previously believed, represent a step towards balancing the energy budget of E. superba in Antarctic waters.

Bone histomorphometry, bone mass, and related parameters in alcoholic males.

Abstract: Bone mass and related metabolic variables were studied in 50 males known to be, or to have been, regular alcohol abusers. Subjects were divided into those who were still drinking and those who had abstained for at least 3 months, and the former further subdivided into moderate and heavy drinkers. Twenty-five had at least two atraumatic spinal crush fractures. In 25 cases, bone histomorphometry was carried out. Lumbar bone mineral density and iliac crest bone volume were significantly lower in spinal crush fracture cases. Parathyroid hormone, testosterone, and urinary cortisol measurements showed no difference between groups. Alkaline phosphatase and 24-hour urine hydroxyproline were higher in osteoporotics than in nonosteoporotics. On bone histomorphometry, there were essentially no differences between those with and those without fractures in terms of bone formation and resorption parameters. Drinkers showed lower osteoid seam width and fraction of osteoid covered by osteoblasts, as well as fewer osteoblasts per 10 cm of bone surface than abstainers. Mineralization lag time was prolonged, and mineralization rate per day was lower in the drinkers. Osteon formation time was prolonged in the drinkers. On the resorption side, only the osteon resorption time was significantly different in the drinkers, being prolonged. The heavy drinkers, but not the moderate drinkers, had a significantly reduced surface extent of lacunae. We conclude that alcohol consumption has clear detrimental effects on bone formation with less pronounced suppressive effects on bone resorption. In no biochemical or hormonal measurement, however, with the exception of hydroxyproline excretion and plasma alkaline phosphatase, could those who had osteoporosis be distinguished from those who did not.

Poker players' pneumonia. An urban outbreak of Q fever following exposure to a parturient cat.

Abstract: Q FEVER, a zoonosis caused by the rickettsia Coxiella burnetii, is endemic in many parts of the world. Cattle, sheep, and goats are the primary animal reservoirs of infection.1 Humans become infect...

Heterozygosity and growth in marine bivalves: further data and possible explanations.

Abstract: In a natural population of two-year-old mussels, shell length was correlated with degree of heterozygosity. There was no correlation between an individual's glycogen level and its degree of heterozygosity, but when individuals were grouped in heterozygosity classes a near-significant correlation was observed between degree of heterozygosity and mean glycogen level corrected for the effects of sex and stage of gonad development. There was no correlation between degree of heterozygosity and index of gonad development. Such a correlation would have provided support for the hypothesis (Zouros and Foltz, 1984) that dependence of time of spawning on heterozygosity may explain the observed heterozygote-deficiency. The causes of heterozygote-deficiency, a com- mon phenomenon in populations of marine bivalves, remain obscure. The observed heterozygosity- growth correlation is examined in the light of the controversy of whether allozymes act as markers in linkage association with genetic conditions that are responsible for the differences in growth among individuals or are themselves the agents of the correlation. The observations that 1) the contributions of individual loci to the correlation vary among populations, 2) the correlation is observed in samples from natural populations but not among progeny from pair matings, and 3) the correlation is nearly always accompanied with heterozygote-deficiency in the population are more compatible with the first explanation and suggest that the growth-heterozygosity correlation results mostly from associative overdominance and to a lesser extent from the direct contributions of scored loci to growth.