Theoretical and experimental derivation of the function relating the size distribution of spherical particles in a volume element to that obtained from images of sections taken through it

Summary The mathematical formulation of three classes of theories concerning the problem outlined in the title of this study was critically assessed and experimentally evaluated. It was found that only one class of the theories describes the relation between the distribution of particles in a volume element to that observed in sections through this volume in a satisfactory way. The errors in the remaining two classes could be traced and the corrections made after a mathematically rigorous analysis brought these theories to comply with a model which, as we could prove experimentally, deserves a high level of confidence.Supported by a grant from the Medical Research Council of Canada.In partial fulfillment of the requirements for obtention of the degree of a Master of Science. Supported by a Studentship from the Medical Research Council of Canada.Scholar of the Medical Research Council of Canada.     

Analysis of a model for antagonistic muscles

In the present work a linear model for a pair of antogonistic muscles is analysed. Each constituent muscle in this model is identical to ones considered previously (Stein and Ouztöreli, 1976). Analytical properties of the antagonistic muscles and dynamics of the system are described and some numerical results are discussed. The natural modes of the system are determined by a fourth order polynomial, which most commonly has one pair of conjugate complex roots and two negative real roots. The filtering of neural inputs through the active state properties of the muscle increases the order of the system to fifth order for these inputs.This work was partly supported by the National Scientific and Engineering Research Council of Canada Grant NRC-A4345 and by the Medical Research Council of Canada Grant MRC-MT-3307 through the University of Alberta     

Effects of elastic loads on the contractions of cat muscles

The nerves to plantaris and soleus muscles in the cat were stimulated with maximal single shocks and with random stimulus trains which produced partially fused contractions. In order to obtain information on the mechanism of muscular contraction, the effects of allowing the muscles to shorten against various elastic loads were studied in the time domain and in the frequency domain. When springs of increasing stiffness were placed in series with the muscle, the twitch tension increased greatly. The gain of the frequency response curve was also much greater with stiffer springs. The shape of the frequency response curve for plantaris muscle could usually be described by that expected for a second-order system with two real time constants or rate constants. The rate constants changed in qualitatively similar ways in response to increased stiffness of an elastic load, increased muscle length and increased mean rate of nerve stimulation. These results are in agreement with the hypothesis that the linear responses of muscles working against elastic loads are determined by the values of two rate constants. Thus, of the many processes associated with contraction, only two are rate-limiting: one associated with the viscoelastic properties of muscle and the second associated with the reuptake of Ca into the sarcoplasmic reticulum. Non-linear aspects of muscular contraction are also discussed. These are more prominent in soleus muscle than in plantaris muscle.Graduate student of the Medical Research Council of Canada.Formerly a Post-doctoral Fellow of the Muscular Dystrophy Association of Canada.     

Predator-prey systems with group defence: The paradox of enrichment revisited

The main concern of this paper is with survival or extinction of predators in models of predator-prey systems exhibiting group defence of the prey. It is shown that if there is no mutual interference among predators, enrichment could result in their extinction. However, if there is mutual interference, the predator population survives (at least deterministically). Research partially supported by the Natural Sciences and Engineering Research Council of Canada, Grant No. NSERC A 4823. Research partially supported by a Natural Sciences and Engineering Research Council of Canada postdoctoral fellowship.     

Smooth endoplasmic reticulum proliferation in mouse enterocytes induced by fructose feeding

Summary Adult male mice receiving a fructose diet show, after three days, a large proliferation of the smooth endoplasmic reticulum in the jejunal absorptive cells. This extension is a secondary stage of the trememdous increase of the glucose-6-phosphatase activity and seems to result from a crypt regulation. Glucose feeding does not provoke the same morphologic changes. This work was supported by a research grant from the Medical Research Council of Canada. Dr. D. Maestracci Ph. D. is a recipient of a Centennial Fellowship of the Medical Research Council of Canada. Mr. D. Ménard is a recipient of a studentship of the Medical Reserach Council of Canada. The authors are greatly indebted to Mrs. S. Sinave for her skillful technical assistance.     

Global dynamics of a selection model for the growth of a population with genotypic fertility differences

A population growth model is considered for a one locus two allele problem with selection based entirely on fertility differences. A local stability analysis is carried out for the critical points — which include possible polymorphic states — of the resulting nonlinear differential equations. The methods of dynamical systems theory are applied to obtain limiting genotypic proportions for every initial state. Thus the results are global and there are no periodic solutions.Research for this paper was partially supported by the National Science and Engineering Research Council of Canada Grant NSERC A-8130Research for this paper was partially supported by the National Science and Engineering Research Council of Canada Grant NSERC A-4823Research supported by NSF Grant MCS 7901069. A portion of the work was carried out while the author was a Visiting Professor at the University of Utah, Salt Lake City, Utah     

A kinetic study of muscular contractions

Summary In the present work the kinetics of muscular contractions are studied, based on a three-state model which is introduced in Section I. The general properties of this class of models for muscular contractions are derived in Sections II–VI. The kinetic equations are solved for four particular examples in Sections VII–X. These analytical results should be useful for comparison with experimental data to determine the functional dependence of the rate constants and on muscle length.This work was partly supported by the National Research Council of Canada Grant NRC-A4345 and by the Medical Research Council of Canada Grant MRC-MA-3307 through the University of Alberta.     

Evolutionary games for spatially dispersed populations

An evolutionary game model is developed that incorporates both spatial dispersion and density effects in the evolutionary dynamic. It is shown that a stable equilibrium (e.g. an evolutionarily stable strategy) of the non-dispersed frequency dynamic becomes a stable equilibrium of the larger system if population density stabilizes at these fixed frequencies. It is also shown, by example, that other equilibria, whose frequencies change from one location to another, may appear when dispersal rates are relatively small.Research supported by Natural Sciences and Engineering Research Council of Canada Operating Grant A6187Research supported by Natural Sciences and Engineering Research Council of Canada Operating Grant A7822     

The development of sites of metaplastic change in regenerating tendon

Summary The development of cartilage and bone in the regenerating segment of the tendon of Achilles following transection has been studied with regeneration taking place in situ, and also following transplantation to a subcutaneous site. Prior to transplantation regeneration was allowed to proceed in situ for various periods of time.It was observed that cartilage and bone develop from the cells of certain pre-cartilaginous areas which represent a metaplasia from fibroblasts. Transplantation to the subcutaneous site at a stage of regeneration when pre-cartilaginous or cartilaginous foci are present leads to the eventual development of bone in the transplant. Transplants made prior to the development of pre-cartilage or cartilage do not show bony metaplasia.It is concluded that the tension of muscle pull is a factor stimulating the metaplastic transformation of fibroblasts to chondroblasts, but once this transformation has occurred the progression to bony metaplasia continues, independently of tension.Supported by a grant from the Medical Research Council of Canada.     

Mitochondrial malic enzyme in mosaic skeletal muscle of mouse chimeras

The question was investigated whether mitochondria in the mammalian skeletal muscle fiber syncytium incorporate gene products encoded by one or many nuclei. Mouse chimeras were produced from strains which differ in their electrophoretic variants of the nuclear-coded mitochondrial protein, malic enzyme (MOD-2, E.C. 1.1.1.40, l-malate NADP⁺ oxidoreductase decarboxylating). The MOD-2 phenotypes of skeletal muscles of these chimeras were characterized in a starch gel electrophoretic system. The results indicate that individual mitochondria can contain products encoded by multiple nuclei and therefore that, for skeletal muscle mitochondria, the cell is not subdivided into nuclear territories. Possible mechanisms of gene product distribution in skeletal muscle fibers are discussed.This work was supported by Grants MT-1940 (K. B. F.) and MA-6411 (A. C. P.) from the Medical Research Council of Canada, and by the Muscular Dystrophy Association of Canada (A. C. P. and P. M. F.).     

Purification and properties of two distinct groups of ADH isozymes from Chinese hamster liver

Two major classes of alcohol dehydrogenase isozymes have been purified from Chinese hamster liver. The two isozyme classes have the same subunit molecular weights but different electrophoretic mobilities. They have a similar range of substrates but different KROM values and sensitivities to the inhibitor pyrazole. The ADHs are immunologically related as determined by Ouchterlony double diffusion experiments. These results suggest that the isozymes are encoded by different structural gene loci derived from a common ancestral gene.Financial support was provided by the National Cancer Institute of Canada and the Medical Research Council of Canada, Grant MT4860. J.-P. Thirion is a Research Scholar of the Science Research Council of Quebec.     

Circadian rhythm of alkaline phosphatase activity in the Golgi zone of mouse duodenal enterocytes

Summary Alkaline phosphatase activity has been analyzed by biochemical methods on mouse duodenal homogenates and by cytophotometric method over the Golgi region of the duodenal cells, at different time periods of the day in fasting and nonfasting animals. A circadian variation of the activity has been observed with a peak at 9.00 h and a nadir at 15.00 h in the homogenates. On the contrary, the cytophotometric measurements have shown a maximal activity over the Golgi zone at 15.00 h and a minimal activity at 9.00 h. These observations are compared with other circadian variations of intestinal enzymes.This work was supported by a research grant of the Medical Research Council of Canada.M. Laurendeau D. is a recipient of a studentship of the Medical Research Council of Canada.     

The dye-exclusion test for cell viability: Persistence of differential staining following fixation

Summary A method is described whereby the differential staining of viable and nonviable unfixed cells, as observed by the dye-exclusion method, can be reproduced in glutaraldehyde-fixed preparations by staining with alcian blue. The results suggest that the differential staining is due, at least in part, to structural differences that are retained following aldehyde fixation. This work was supported by grants from the National Cancer Institute of Canada and the National Research Council of Canada. Recipient of a Research Studentship from the National Cancer Institute of Canada.     

Mitochondrial myelin-like figures: A non-specific reactive process of mitochondrial phospholipid membranes to several stimuli

Summary Small concentric arrays resembling myelin figures were found in the liver cell mitochondria of fasted rats, of fasted rats given insulin and glucose, and of untreated fed rats. In addition to myelin-like figures, interdigitation of the membranes of adjacent mitochondria were common and often formed chains of mitochondria. Fusion between the outer membranes of mitochondria and protrusions of part of one mitochondrion into another were also found. Since mitochondrial myelin-like figures were even occasionally observed in control fed animals and since identical structures have been described in a number of unrelated conditions, it is concluded that they are not aetiologically specific. The myelin-like figures are considered to represent a form of focal mitochondrial phospholipid membrane degeneration under various stimuli.This work was supported by the Medical Research Council of Canada, the Banting Research Foundation and the Canada Arts Council.     

Predictions and ecperimental tests of a visco-elastic muscle model using elastic and inertial loads

A simple, linear visco-elastic model of muscle is described which contains five parameters: a series and a parallel elasticity, a viscosity, and a magnitude and rate constant for the decay of the active state. The effects of adding springs in series with a muscle are predicted. The responses to random stimulus trains can be used to evaluate the parameters of the model. The effects of applying inertial loads to the muscle can also be predicted. These predictions are in good agreement with experimental observations on plantaris muscle of the cat. For example, damped oscillations of the predicted frequencies can be observed for various inertial loads. The gain of the frequency response falls off sharply (as the fourth power of frequency) at higher frequencies. However, responses to lower frequency signals, including most of the frequencies important for cyclic movements, are only slightly affected by a wide variation in inertial load.Graduate student of the Medical Research Council of Canada.Formerly a Post-doctoral Fellow of the Muscular Dystrophy Association of Canada.     

Electron microscopic histochemistry of lysosomes in neurosecretory nerve endings and pituicytes of rat posterior pituitary

Summary Electron microscopic localization of acid phosphatase (AcPase) was carried out on posterior pituitary glands from rats. An estimated 5% of the neurosecretory nerve terminals contained structures which showed reaction product. Most of the lysosomes were small dense bodies, often with a membranous substructure. Other lysosomes were larger in size or were found within vacuoles. AcPase was also localized to lysosomes and the Golgi apparatus of pituicytes. Evidence is presented which would associate the large lipid droplets characteristic of pituicytes with AcPase-positive dense bodies. The present study indicates that hydrolytic activity by lysosomes occurs within the terminals of neurosecretory cells, and adds further support to the concept that this process represents a normal phenomenon of cells and their extensions in general.Supported by the Medical Research Council of Canada.Medical Research Associate of the Medical Research Council of Canada.     

Optimal task performance of antagonistic muscles

Movements against a variety of loads are relatively invariant in form. These movements are controlled in general by antagonistic groups of muscles. In this paper optimal control strategies are computed for coupling antagonistic muscles so as to minimize deviations from a desired trajectory. Simulations are presented for linear and nonlinear decision functions linking control of the two muscles for a variety of movements in a way that may be compared with experimental observations.This work was partly supported by the Natural Sciences and Engineering Research Council of Canada Grant NSERC OGP-4345 and by the Medical Research Council of Canada Grant MRC PG-47 through the University of Alberta     

Red-light-enhanced conversion of tritiated gibberellin A9 into other gibberellin-like substances in homogenates of etiolated barley leaves

Summary Irradiation of homogenates of etiolated barley leaves with red light resulted in an increase in the levels of gibberellin (GA)-like substances as compared to dark controls. When homogenates were fed with [³H]-GA₉ there was as incorporation of the radioactivity into a number of other GA's: this process occurred to a greater extent in red light than in darkness, and could be inhibited by boiling the extract prior to addition of the [³H]-GA₉.Supported by National Research Council (Canada) grant A-5727 (Dr. D. M. Reid).Supported by National Research Council (Canada) grant A-2585 (Dr. R. P. Pharis).Supported by NATO-Science Research Council (U. K.) Postdoctoral Fellowship.     

Ultrastructural localization of glutamic oxalacetic transaminase activity in cardiac muscle fiber and cardiac mitochondrial fraction of the rat

Summary The ventricular heart muscle of the rat was fixed in glutaraldehyde-formaldehyde mixture. The tissue blocks were incubated in a medium containing 20 mM 1-aspartic acid, 2 mM -ketoglutaric acid and 6 mM lead nitrate as major ingredients. The enzymatic reaction product due to glutamic oxalacetic transaminase (GOT) activity was found to be localized in the cristae and at the surface of the mitochondria, in the cisternae of the nuclear envelope and in the sarcoplasmic reticulum. Isolation of the mitochondrial fraction from the homogenate of the fixed heart muscle was performed, and GOT activity in this fraction was demonstrated both histochemically and biochemically.This Work was Supported by a Research Grant from the Medical Research Council of Canada (MA-3340).     

Application of optimal multichannel filtering to simulated nerve signals

The optimal linear filters derived in the preceding paper can be thoroughly evaluated using computer simulations, based on the properties of mammalian sensory and motor nerve fibres. Using reasonable values for action potential waveforms, conduction velocity and electrode noise, good separation of motor and sensory signals can be obtained. The performance of the filters is degraded by 1) increasing the electrode noise, 2) introducing dispersion in the conduction velocities, or 3) variation in the waveform of the action potentials from that used in designing the filters. However, the variations needed to seriously degrade performance are quite large compared to those which are likely to be present in mammalian nerves. Use of these filters to distinguish different classes of sensory (or motor) signals based on conduction velocity is discussed.This work was partially supported by the Technical Research Council of Denmark (Grant 516-6703.E406), the Medical Research Council of Canada (Grant MRC-MT3307) and the National Research Council of Canada (Grant NRC A-4345)