Showing papers by "University of Amsterdam published in 1971"

On the nature of turbulence

Abstract: A mechanism for the generation of turbulence and related phenomena in dissipative systems is proposed.

Circus Movement within the AV Node as a Basis for Supraventricular Tachycardia as Shown by Multiple Microelectrode Recording in the Isolated Rabbit Heart

Abstract: Supraventricular tachycardia in an isolated rabbit heart preparation was repeatedly initiated and terminated by carefully timed atrial premature beats. Transmembrane action potentials of AV nodal cells were recorded simultaneously by a "brush electrode" consisting of 10 microelectrodes. Surface electrograms of atrium and His bundle were also recorded. The moments of activation of 54 different AV nodal cells, both during regular driving of the atrium and during tachycardia were ascertained. Premature atrial beats introduced during tachycardia would either "reset" the tachycardia or terminate it. The sequence of activation of the AV nodal cells when initiating tachycardia, during tachycardia itself, and when premature beats were interpolated during tachycardia warrant the conclusion that a circus movement in the AV node, based on functional longitudinal dissociation of the upper AV node, was the underlying mechanism of the arrhythmia.

Host-Parasite Interrelationships Between the Freshwater Pulmonate Biomphalaria Pfeifferi and the Trematode Schistosoma Mansoni

Abstract: The influence of infection with S. mansoni on reproduction, growth, food consumption and survival in B. pfeifferi was studied experimentally (Ch. II). The prepatent period in infected snails was shown to last 22-24 days under the conditions prevailing in the relevant experiment. The number of eggs laid by infected snails as compared with controls was significantly reduced from 7-10 days postinfection onwards. After day 13 postinfection it was completely suppressed in the majority of the infected snails. The increase in shell diameter in infected specimens was larger than that of the controls between 7 and 18 days, that in weight between 11 and 21 days postinfection. Gigantism did not occur. There was no difference in mortality between infected and control snails prior to the 11th week after the beginning of the experiment. After that, the mortality among infected specimens showed a sharp rise. Uninfected and infected snails consumed similar amounts of food (dried lettuce) in the first two weeks of the experiment. After that, infected snails consumed less food than controls. The digestive gland of B. pfeifferi was studied with histological, histochemical and ultrastructural methods (Ch. III). The highly folded epithelium of the ducts connecting the digestive gland with the pyloric part of the stomach, consists of cilia and/or microvilli bearing columnar cells with interspersed mucous cells. In the epithelium of the digestive gland two main cell types are distinguished: the digestive cell and the secretory cell. In addition some mucous cells occur. It is concluded that the main functions of the digestive cell are absorption and endocytosis of predigested food material, followed by intracellular digestion. Indigestible residues are accumulated in a large vacuole, which eventually is excreted. The secretory cell produces and secretes proteinaceous substances, presumably digestive enzymes. It does not store calcium. The so-called excretory cells, which are in fact degenerating secretory cells, have vacuoles containing yellow globules. These yellow globules together with cell debris are finally released into the lumen of the digestive gland. The observations indicate that the digestive gland is not important as a storage organ for reserve material. The lobules of the digestive gland are covered by a thin connective tissue sheath, consisting of ground substance, collagen-like fibrils, smooth muscle cells and cells with the appearance of pigment cells. The connective tissue between the lobules of the digestive gland and the acini of the ovotestis, and between these organs and the mantle, consists mainly of vesicular connective tissue cells. These cells are supposed to play an important metabolic role as storage cells for glycogen. The tegument of the daughter sporocyst of S. mansoni (Ch. IV), consisting of an outer syncytial anucleate layer which is joined by cytoplasmic connections to nucleated cell bodies (tegumental cells), has the same basic architecture as that described for various stages of trematodes and cestodes. Well-developed mitochondria, GER cisternae and tubules, free ribosomes and polysomes, and lipid droplets occur throughout the tegument. The ultrastructural features suggest that the outer layer is involved in uptake of nutrients by absorption and endocytosis. The poorly developed musculature is loosely arranged in two layers beneath the outer tegumental layer. The nucleated portions of the muscle fibres are situated between the tegumental cells. The protonephridial system consists of flame cells with efferent tubules. The bundle of cilia, implanted in the flame cell, beats in the cilia chamber or barrel. The proximal part of the barrel consists of alternating rib-like extensions of the flame cell and of the first tubule cell, respectively. Ultrafiltration probably takes place in the ribbed part of the barrel. The development of cercariae from germinal cells is briefly described. The pathological effects of infection with S. mansoni on the digestive gland epithelium of B. pfeifferi (Ch. V) are limited. From about 12 weeks after infection slight changes occur, but they are difficult to distinguish from changes due to ageing of the cells. The effect of starvation on the digestive gland epithelium is much more marked than the adverse influence of infection. Compression of digestive gland lumina by daughter sporocysts was not observed. Changes in the connective tissue of the digestive gland due to the presence of daughter sporocysts were: development of muscle cells into cells with the appearance of pigment cells and/or degeneration of these muscle cells, and an increase in the number of amoebocytes, which become involved in the elimination of cell debris and in the formation of a loose layer over the parasites.

Effect of an Early Atrial Premature Beat on Activity of the Sinoatrial Node and Atrial Rhythm in the Rabbit

Abstract: In the spontaneously beating isolated right atrium of the rabbit, premature beats were elicited by electrical stimulation. When the premature beat was elicited early in the atrial cycle, the postextrasystolic pause had a short duration and the sum of the pre- and postextrasystolic pause was about the same as the duration of a normal spontaneous interval. We have tried to demonstrate, using simultaneous multiple microelectrode impalements of SA node fibers, that by such an early atrial premature beat the atrium could be activated by a reentrant mechanism. The results of our experiments led us to the conclusion that the impulse of the premature beat, elicited early in the atrial cycle, discharges the SA node only fractionally and that the fibers in the neighborhood of the activated area are influenced electrotonically. This causes a change of both the site and the moment of the spontaneous impulse formation. The SA node discharges spontaneously after such an early premature beat. Reentry activation is likely to occur when a series of atrial premature beats is observed. A supraventricular tachvcardia might be caused by repeated atrial discharges following a stimulus very shortly after the atrial refractory period.

Relation between egg production and food consumption in species of the genus Pardosa (Lycosidae, Araneae) under experimental conditions of food-abundance and food-shortage.

Abstract: 1. The amount of food intake during the egg ripening period and the conversion of this food into eggs (biomass and number of eggs) in four Pardosa species is described. The amount of food taken in is dependent on the size of the spider species. Basically the process of conversion of food into egg-biomass is the same for all four species. Thus the size of the spider species mainly determines the number of eggs in the egg-sac. There are however minor differences in “efficiency” of the process and in dryweight of the eggs between the species. These differences which are discussed complicated the general process of food conversion into number of eggs. 2. When food shortages are supplied during the egg ripening period two reactions can be observed: a) All species tend to keep the dry weight of the eggs at a constant level. b) Some species produce the same number of eggs under conditions of small food shortages as under conditions of maximum food supply, using reserve material from the body of the female. In this case the female either shows no increase in body weight or a decrease while others immediately adapt the number of eggs to the quantity of food given.

Fracture Faces in the Cell Envelope of Escherichia coli

Abstract: Freeze-fracturing of Escherichia coli cells in the presence of 30% (v/v) glycerol resulted in a double cleavage of the cell envelope exposing two convex and two concave fracture faces ([Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text]) with characteristic patterns Complementary replicas revealed the relationship of the fracture faces to their corresponding fracture planes The inner fracture plane splits the plasma membrane at one particular level Apparently the outer fracture plane was located in the outer part of the wall, as it was separated by a layer ([Formula: see text]) from the fractured profile (CW1) presumably corresponding to the murein layer The outer fracture plane did alternate toward the cell periphery, exposing complementary smooth areas ([Formula: see text] and [Formula: see text]) When cells were freeze-fractured in the absence of glycerol, the outer cell surface appeared as an etching face rather than a fracture face A schematic representation of the relative location of the different fracture faces in the E coli cell envelope is given

Distribution and Ultrastructure of Epidermal Sensory Cells in the Freshwater Snails Lymnaea Stagnalis and Biomphalaria Pfeifferi

Abstract: The epidermal receptor cells and their distribution throughout the body surface of Lymnaea stagnalis and Biomphalaria pfeifferi were studied by means of light and electron microscopic techniques. The investigations reveal general agreement between the two species. The receptor cells are primary sensory nerve cells with the cell bodies lying below the epidermis. The subepithelial cell bodies are frequently grouped together forming small ganglia, particularly in rich sensory regions, such as the lips and the tentacles. Dendrites extend from these sensory cell bodies between the epidermal cells and form free nerve endings at the surface of the epidermis. Six different types of free nerve endings are distinguished on the basis of the number of cilia present and on the length and structure of the cilia roots. A survey of the distribution of the sensory cells revealed that they are restricted primarily to the tentacles, lips, front edge of the foot, pneumostome and mantle edge, although they are also present in the dorsal and lateral surface of the foot. No free nerve endings were found in the dorsal head epidermis. Only one type of nerve ending was found to have a specific localization, whereas the other types have a general distribution. Although it is difficult to determine the function of the different types of free nerve endings in an ultrastructural study, some suggestions are made on the basis of morphological comparisons with receptor cells in other species and also on the basis of behavioral and physiological experiments which have been performed on L. stagnalis.

Late Weichselian Palaeomagnetic Reversal

Abstract: AS part of the joint European work on the establishment of a world standard section for the Pleistocene/Holocene boundary, an oriented core 14.5 m long was taken with the Swedish foil piston corer in the Botanical Garden of Gothenburg (south-west Sweden). The core, B 873, extends in time from about 12,600 to 8,600 BP, that is, from the early part of the Agard Interstadial to the middle of the Boreal (Fig. 1). Core B 873 was analysed for stratigraphy, water content, grain size distribution, organic matter, carbonate, clay minerals, molluscs (Morner), pollen (Berglund), diatoms (Bjorn-Rasmussen and Du Saar), ostracods (Du Saar), forams (Feyling-Hansen), radiocarbon (Hakansson) and palaeomagnetism (Lanser and Hospers).

Formation, storage, and release of neurosecretory material studied by quantitative electron microscopy in the fresh water snail Lymnaea stagnalis (L.).

Abstract: The process of neurosecretion in the fresh water snail Lymnaea stagnalis was analysed quantitatively at the ultrastructural level. Special attention was paid to the phloxinophilic neurones in the cerebral ganglia, the Caudo-Dorsal Cells (CDC). The rates of synthesis, storage and release of neurosecretory elementary granules were studied in the CDC of animals fixed at time intervals of 4 hours, during a 24 hour period. The processes concerned show a diurnal rhythmicity. In the cell bodies synthetic activity, as determined by counting the number of active golgi zones per surface unit, is high during the night and low during the day. The reverse was found for the amount of secretory material (number of elementary granules per surface unit) stored in the cytoplasm. From these results it is concluded that also the rate of transport of the elementary granules through the axons fluctuates rhythmically. It has its maximum during the night and its minimum during the day. This conclusion was substantiated by the observation that the highest number of granules in the axons is found during the night. The axon terminals of the CDC pass through four different stages during the 24 hour period. In axons being in the accumulation stage, which are found from the morning until the evening, the number of elementary granules increases rapidly. The neurohaemal zone increases in thickness during this process. In axons in the release stage, which predominate during the evening and the night, the contents of the elementary granules are extruded from the axon terminals, apparently by exocytosis. The rate of release of the secretory material into the body fluid, which is very low during the day, shows a rapid increase a few hours before sunset, and is probably correlated with the light intensity. A marked decrease of the amount of secretory material is noted in the neurohaemal area during the release stage. A daily turnover of nearly all secretory material accumulated in the axon terminals is suggested by the observations. Axons being in the reconstruction stage are mainly found during the night. They are distinguished by the presence of vesicular and tubular structures. These probably originate by fusion of microvesicles, which are considered to arise from the membranes of the elementary granules after exocytosis. After disappearance of the vesicles and tubules the axons enter the empty stage. This is frequently found in the night and in the early morning hours. In the morning the axon terminals enter the accumulation stage again. Furthermore, accumulation and release phenomena were quantified in the axon terminals of 5 other neurosecretory cell types present in the ganglia. A diurnal pattern rather similar to that of the CDC was found in the Light Green Cells (the Medio- and Latero-Dorsal Cells in the cerebral ganglia). No rhythmicity was found in the neurohaemal areas of the four types of secretory neurones located in the ganglia of the visceral ring. A constant level of storage and release was established during the 24 hour period. The relationship between synthesis, storage and release of the secretory material of the CDC is discussed.

Physiological parameters of mental load.

Abstract: The term mental load can be used for the implications of tasks calling on the information handling capacity of man. The essential aspects of the terms ‘ load ’ and ‘ capacity ’, as used in work physiology, are valid for mental load in the following ways: the question of the physiological ‘ costs ’ (biological consequences) of a given performance; external load to be measured in units of performance/time (signals/time, choices/time); capacity, dependent on time of endurance; physiological changes correlating with load; pathological symptoms due to extreme load. An experiment is discussed, where a simple binary choice task is used with several frequencies of signals to be answered; thus providing different loads. Systematic changes were found in heart frequency, sinus arrhythmia, systolic and diastolic blood pressure, rate of respiration, and so on. Arguments are put forward that these changes are due to a simultaneous rise in sympathetic and in vagal tone.

The mesosome of bacillus subtilis as affected by chemical and physical fixation

Abstract: The reliability of structures observed with electron microscope techniques represents a general problem in ultrastructure research . Obviously, every technique employed will have its limitations . Unfortunately the limitations are incompletely understood, and the eventual image obtained by electron microscopy deviates to an unknown extent from reality . The experimental approach to this problem is not an easy one . However, the effects of chemical fixation on the preservation of ultrastructure can, within limits (9), be studied by means of freeze-fracturing. In previous studies (8, 9) some of these effects were studied on young cells of Bacillus subtilis, strain Marburg . Freeze-fracturing after chemical fixation according to the Ryter-Kellenberger tech-

The Effect of Temperature and Ionic Strength on the Electrophoretic Mobility of Yeast Mitochondrial RNA

Abstract: The electrophoretic mobilities of mitochondrial and cell-sap ribosomal RNAs from Saccharomyces carlsbergensis have been measured relative to the mobility of Escherichia coli rRNA in 2.4% polyacrylamide gels at various temperatures and ionic strengths. At 5° C and in 20 mM sodium acetate, 40 mM Tris-acetate, 2 mM EDTA (pH 7.8), mitochondrial and cell-sap rRNAs co-migrated and were only partially resolved from E. coli rRNA. When the temperature of electrophoresis was increased the mobility of the mitochondrial rRNAs (and to a lesser extent of the cell-sap rRNAs) decreased relative to the mobility of the E. coli rRNA species, reaching a minimum between 9 and 16° C. As a consequence the mitochondrial and cell-sap rRNAs were completely resolved in this buffer at temperatures above 9° C. Similar effects of temperature on relative electrophoretic mobility were observed in 90 mM Tris-borate buffer at pH 8.3 and the effect was even more pronounced at low ionic strength (10 mM NaCl, 5 mM Tris-HCl, 2 mM EDTA, pH 7.5). At low ionic strength the decrease in the relative electrophoretic mobility of mitochondrial rRNA with an increase in temperature was accompanied by a decrease in sedimentation coefficient from 21–22 S (large component) and 14 S (small component) at 5° C to 16 and 11.5 S at 20° C (calculated in relation to assumed S-values of 23 and 16 S for the rRNA species of E. coli). We conclude that the electrophoretic mobility of RNA in polyacrylamide gels is more dependent on secondary structure than previous work had suggested and that caution is needed to interpret the relative mobility of mitochondrial RNA on gels in terms of molecular weight. In addition, our results show that judicious variation of temperature and ionic strength may allow the separation on gels of RNA mixtures that cannot be resolved under standard conditions.