Showing papers by "University College London published in 1973"

The Logic of Animal Conflict

Abstract: Conflicts between animals of the same species usually are of “limited war” type, not causing serious injury. This is often explained as due to group or species selection for behaviour benefiting the species rather than individuals. Game theory and computer simulation analyses show, however, that a “limited war” strategy benefits individual animals as well as the species.

Calcium Ionophores and Movement of Calcium Ions following the Physiological Stimulus to a Secretory Process

Abstract: Mast cells can be induced to secrete histamine by an ionophore, the action of which depends on the presence of calcium within a specific concentration range. The fact that labelled calcium can be seen to enter sensitized cells during histamine secretion in the presence of antigen suggests that the entry of calcium into the mast cell may be the trigger for the release of histamine.

Transmitter Release Induced by Injection of Calcium Ions into Nerve Terminals

Abstract: Calcium ions injected into the presynaptic nerve terminal in the giant synapse of the squid, evoked transmitter release while similar doses of Mg and Mn were ineffective The transmitter release induced by intracellular application was still observed when Ca was replaced in the external fluid by Mn, in spite of the fact that this abolished transmitter release in response to presynaptic depolarization

Esterase D: a new human polymorphism

Abstract: Tashian (1 961, 1969) demonstrated several different esterases in human red cells by electrophoresis. Azo dye coupling techniques were used to locate the esterase isozymes. Three main groups of esterases were defined on the basis of their electrophoretic properties, substrate specificities and inhibition characteristics, and were referred to as the A, B and C esterases. Isozymes of carbonic anhydrase, which also has esteratic activity, were also demonstrated using essentially similar techniques. Fig. 1, which is based on Tashian's work, shows a diagrammatic representation of the various red cell esterase isozymes after electrophoresis of haemolysates in borate starch gels at pH 8.0-8-6. The A esterases are subdivided into three sets of isozymes, A,, A, and As, which differ electrophoretically and in their storage properties and inhibition characteristics ; also the As isozymes have a larger molecular size than A, or A,. Inherited variants of these isozymes are rare in man but two different variant phenotypes have been reported (Tashian & Shaw, 1962; Tashian, 1965). They are of particular interest because each of the three subgroups of A esterase are affected in the variant isozyme patterns suggesting that A,, A, and As contain a common subunit. Family studies on one of the variants indicated that this esterase A locus is autosomal. Esterase B is primarily a butyryl esterase and no variants have been reported in population surveys to date. Esterase C is a rather weakly staining invariate acetyl esterase. Several different variants of the carbonic anhydrase isozyme CA I (or B) have been recorded in the literature (see Tashian, 1969) but they are all individually rare except in certain cases where they have been identified in small isolated populations, e.g. the CA I, variant in Guam and Saipan. The CA 1 locus is autosomal and the variants do not affect CA I1 (or C). The latter is determined at a separate autosomal locus and recent studies (Moore, Funakoshi & Deutsch, 1971) using an immunological detection technique have led to the recognition of a genetic polymorphism of CA 11 in Blacks. Another esterase which occurs in red cells is acetylcholinesterase. This is membrane bound and not therefore readily detected by electrophoresis of simple lysates. The present paper describes yet a further human red cell esterase. It will be referred to as esterase D (Es D). It was discovered by the use of the fluorogenic substrates, 4-methyl-umbelliferyl acetate and 4-methyl-umbelliferyl butyrate, for the detection of esterase isozymes after starch gel electrophoresis. The isozymes of this new esterase are different from the red cell A, B aiid C esterases, the carbonic anhydrase isozymes, and from acetylcholinesterase in their

A family of steady vortex rings

Abstract: Axisymmetric vortex rings which propagate steadily through an unbounded ideal fluid at rest at infinity are considered. The vorticity in the ring is proportional to the distance from the axis of symmetry. Recent theoretical work suggests the existence of a one-parameter family, [npar ]2 ≥ α ≥ 0 (the parameter α is taken as the non-dimensional mean core radius), of these vortex rings extending from Hill's spherical vortex, which has the parameter value α = [npar ]2, to vortex rings of small cross-section, where α → 0. This paper gives a numerical description of vortex rings in this family. As well as the core boundary, propagation velocity and flux, various other properties of the vortex ring are given, including the circulation, fluid impulse and kinetic energy. This numerical description is then compared with asymptotic descriptions which can be found near both ends of the family, that is, when α → [npar ]2 and α → 0.

Psoriasis-Liver-Methotrexate Interactions

Abstract: An international cooperative study was organized to evaluate whether the treatment of severe psoriasis with methotrexate significantly affects the liver of these patients. From a study population of 550 patients, 742 liver biopsy specimens together with pertinent clinical and laboratory data were evaluated as a function of methotrexate usage. Factors found to be significantly associated with histologic liver damage include: increased alcohol intake, the daily orally administered methotrexate dosage schedule, obesity, and diabetes. The evidence implicating increasing cumulative methotrexate dosage as a cause of hepatic fibrosis is not clear. Of 247 patients with biopsyproven fibrosis or cirrhosis, 88 patients had no recorded abnormalities in history, physical examination, or laboratory test results which casts serious doubt on the reliability of detecting fibrosis or cirrhosis without a liver biopsy.

On making holes in a sheet of fluid

Abstract: It is suggested in this paper that axisymmetric holes in thin sheets of fluid in which surface tension forces predominate will open out if they are initially large in relation to the thickness of the sheet; but that small holes will close up. No exact criterion has been found for the critical hole size in a free falling sheet, but the behaviour of the sheet may be closely simulated by the suspension of a soap film between coaxial circular rings. Theoretical results and experimental observations on catenoid films so formed are described.For a hole in a sheet standing under gravity on a horizontal plane an equilibrium configuration exists, which is shown to be unstable. It is suggested that in this case the equilibrium position serves to distinguish between holes which open and those which close. Experiments on the behaviour of holes in a mercury sheet reveal a well-defined critical size which is in good agreement with that predicted by the unstable equilibrium.A further series of experiments on holes made in a sheet of water standing on paraffin wax gave no sharp distinction between opening and closing holes, and holes of a wide range of sizes could remain stationary. This behaviour is associated with changes in the angle of contact with the plane. Independent meniscus observations similar to those of Ablett for a steadily moving meniscus show that the angle of contact θa, for a meniscus about to advance is greater than the value θr for a meniscus on the point of receding. It is seen that this difference will produce a range of hole diameters within which a hole will be trapped and remain stationary. Observations on the minimum size of hole on a water sheet which will remain open are reported. But it was found that the largest holes which would remain stationary were too large in relation to the size of the sheet for reliable results to be obtained.

An Anti-Inflammatory Peptide from Bee Venom

Abstract: THE belief that the venom of the common honey bee, Apis mellifira, is beneficial in certain arthritic and rheumatoid conditions goes back to antiquity1. In a study of phospholi-pase-A2,3 we have fractionated nearly 1 kg of freeze-dried bee venom and tested all the fractions for anti-inflammatory activity. Preliminary experiments showed activity to be associated with the basic peptide fraction. The peptides were separated using ‘Sephadex’ G25 and G50 followed by ion-exchange chromatography using either CM ‘Sephadex’ C25 (pH 4.7) or SE ‘Sephadex’ C25 (pH 4.2).

T and B lymphocytes and immune responses.

Abstract: The recognition of two distinct classes of lymphocytes has been a turning point in immunology. Immunological models and tools may help to provide the answers to many biological problems.

Normal Distribution, Patching and Capping of Lymphocyte Surface Immunoglobulin studied by Electron Microscopy

Abstract: Lymphocyte surface Ig is diffusely and randomly distributed in the unperturbed membrane. The binding of divalent antibodies redistributes the membrane immunoglobulin molecules even at 0°C.

Cytochemical and Ultrastructural Differences between Intraspecific Compatible and Incompatible Pollinations in Raphanus

Abstract: Examination of the behaviour of pollen on the style of Raphanus, following compatible and incompatible intraspecific pollinations, has revealed the self-incompatibility system in this species to be composed of at least three stages. The first, on which no information has been obtained in this study, involves the germination of the grain. The second stage concerns the ability of the pollen tube to penetrate the cuticle of the stigmatic papilla. It is possible that cutinase is deficient in incompatible pollen tubes but, in most instances, the outer layers of the stigmatic wall are penetrated. The third stage involves the interaction of substances secreted by the pollen tube with products of the stigmatic cytoplasm. The interaction is swiftly followed by the deposition, in the stigma, of a layered callosic body. This is formed immediately under the point of penetration and takes about 6 h to develop fully. Development of the pollen tube ceases as the first layers of callose are laid down. It is possible that the substances in the pollen responsible for the initiation of the second two stages are held in the tapetally synthesized tryphine, thus accounting for the sporophytic control of pollen compatibility in this species. The mature stigma contains large numbers of crystalline protein bodies, but it is not known whether they play any role in the self-incompatibility system.

Laminar flow over a small hump on a flat plate

Abstract: A boundary layer flows over a flat plate which has on it a small hump situated downstream of the leading edge. The description of the boundary-layer flow, based upon a triple-deck structure, shows how the presence of the hump generates an interaction between the inviscid region just outside the layer and the viscous region near the hump. The pressure force dominant in the boundary layer and the connexion of the local flow with the main stream develop together and are self-perpetuating, and both remain of primary significance for a wide range of hump sizes, even for a hump buried well inside the boundary layer. By consideration of the limiting cases of very small and very large humps, a consistent account of the nature of the disturbances due to the various sizes of hump is produced. The forces and couples on the hump are also evaluated.

Syntheses of Seven‐ and Five‐Membered Rings from Allyl Cations

Abstract: The cycloaddition of allyl cations to conjugated dienes offers an efficient and general tool for the construction of seven-membered carbocycles. The silver salt route is highly suitable for generating allyl cations and can be used even in most difficult cases, i. e. for elusive and intractable allyl cations such as 2-methylallyl, 2-methoxyallyl, and the parent allyl cation. Cycloadditions to the 2-methoxyallyl cation come very close to the prototype of a 6π, 7C reaction, since the carbonyl group introduced into the new ring can either be used for further transformations or be removed altogether. The combination of an allyl cation with π reactants, especially conjugated dienes, is a powerful and strongly convergent synthetic method since it permits one-step assembly, from a C3 and a C4 unit, of a cluster of up to four chiral centers in a ring which is larger than six-membered. Allyl cations combine with electron-rich 2π systems to form novel five-membered rings. The nature of the organometallic intermediates has been elucidated in many cases.

The effect of slip on the motion of a sphere close to a wall and of two adjacent spheres

Abstract: The motion of a sphere towards a plane or another sphere is opposed by the fluid between them with a force which is inversely proportional to the gap. In consequence, it is impossible for a constant force to produce contact in a finite time, unless the Stokes equations are modified. When the gap is of the same order as the mean free path of the air molecules, the Stokes theory for the motion of the air must be modified. The Maxwell slip flow approximation is used in this paper to show that, when the gap is small, the resisting force between the approaching surfaces becomes only logarithmically dependent on the gap, and contact can be achieved in a finite time. The difficulty in applying the Stokes theory to the problem of determining collision efficiencies for cloud droplets is thereby removed. The calculated values of the resistance to approach are used to determine the motion of a sphere falling towards a plane. If the motion is compared with the corresponding motion when no allowance is made for slip flow, the sphere without slip would still be at a distance of 1.3 times the mean free path from the plane, when the sphere with slip has made contact. Transverse motion must also be considered if the trajectory of a particle close to a collector is required. The forces and couples on the sphere in that situation have a logarithmic dependence on the gap without slip, but they tend to constant values when the effect of slip is included. Some calculations of collision efficiency of drops falling under gravity (Hocking and Jonas [1]) have been amended to include the effect of slip when the colliding drops are very close together, and show a significant increase in the collision efficiency.

The formation of the tryphine coating the pollen grains of Raphanus, and its properties relating to the self-incompatibility system

Abstract: The tryphine that coats the pollen grains of Raphanus is tapetally synthesized and is composed of a fibro-granular and a lipidic component. The fibro-granular material is proteinaceous and is secreted by cisternae of the endoplasmic reticulum. The lipidic component is derived, mainly, from degraded elaioplasts. The fibro-granular material is applied to the pollen exine first, followed by the lipidic mass. The tryphine condenses during the final stages of pollen maturation and dries down to form a thick, highly viscous coating. The major part of the condensation appears to result from dehydration. The tryphine, extracted from the pollen by a centrifugal method and mounted in a membrane, appears to be capable of penetrating the outer layers of a stigma of the same species and, if the pollen from which it was derived is incompatible with respect to the stigma, the stimulation of the production of the callosic reaction body in a manner similar to an incompatible pollen tube. It is proposed that, in Raphanus, substances responsible for the initiation of at least two stages in the self-incompatibility system are held in the tryphine.

A Golgi study of the rat dorsal lateral geniculate nucleus.

Abstract: Golgi-Kopsch and Cox preparations of albino rat dorsal lateral geniculate nucleus show two classes of neuron. Class A cells (assumed geniculocortical relay cells) have tufted dendritic arborizations, smooth primary dendrites, occasional excrescence clusters at dendritic branch points, irregular, small excrescences along distal dendrites, and myelinated axons. A subclass, more common medially, has long, smooth, radiating dendrites that branch sparsely. Class B cells are small (c. 10 m dia.) paucidendritic, and commonly bipolar. Their dendrites branch rarely and often run for long distances maintaining a uniform diameter. They are commonly orientated so that their dendrites extend either dorso-ventrally or approximately antero-posteriorly (i.e., parallel to either the representation of the vertical meridian or to the lines of projection). The dendrites bear complex appendages, often branched and several microns long, with en passant and terminal varicosities. Some class B cells also appear to have axons, but conclusive evidence is lacking. Class B cells may be intrinsic neurons, corresponding to the electrophysiologically identified inhibitory interneurons and to cells seen by electron microscopy to have presynaptic perikarya and dendrites. The complex dendritic appendages probably enter synaptic glomeruli within which they establish pre- and postsynaptic contacts. Whether class B cells are comparable with the Golgi type II cells of other thalamic nuclei remains an open question. Three classes of axons are also described, and their possible origins considered.

Quantitative photogrammetric analysis and qualitative stereoscopic analysis of SEM images

Abstract: SUMMARY This paper is concerned with methods for obtaining three-dimensional (3D) information from scanning electron microscope (SEM) images. It may come as a surprise that this topic merits separate discussion, because, it is generally accepted that every SEM image of a rough surface using the secondary electron emission mode gives apparent 3D information. This is true to some extent, since SEM images are comparable with photographs of rough surfaces illuminated with light coming from one direction, but our main concern here will be with 3D visualization from stereoscopic pairs of images. However, there are other ways in which 3D information may be obtained, even in the SEM, and these are considered first. The remainder of the paper is largely concerned with the use of stereoscopic parallaxes, whether or not they are visualized as such. Commonly used methods for viewing stereo-pairs are described, followed by simple methods for measuring stereoscopic parallaxes. Formulae for reducing linear measurements in the two photographs to real height differences are given.

Theta-bearing lymphocytes in nude mice.

Abstract: MICE homozygous for the mutation nude (nu/nu) are hairless1 and deficient in thymus2–4 and thymus-derived (T)5,6 lymphocytes. They are generally referred to as being athymic and are widely used in immunology as a source of B lymphocytes uncontaminated with T cells, although there is evidence that the thymus is present, but is small and dysplastic3,4. Indirect evidence has suggested that at least some nude mice have small numbers of T cells7–9, but this has been controversial. I report here the direct demonstration by immunofluorescence of a small population of θ-bearing cells in lymph nodes and spleens of nude mice using fluorescein-conjugated anti-θ antibody.

Mobility of concanavalin A receptors in myelin and synaptic membranes.

Abstract: THERE is now abundant evidence that biological membranes are fluid in nature with constituent protein and lipid molecules able to move relative to one another in the plane of the membrane1–6. In cells that occur in the unassociated state such as lymphocytes, surface macromolecules appear to be randomly distributed in the membrane unless cross linked by multivalent antibodies or plant lectins when they undergo a striking redistribution, passively clustering into patches and sometimes actively coalescing to form a “cap” at one pole of the cell3,5–11. No conclusions can be drawn from these experiments with unassociated cells regarding the conditions within cellular membranes of highly organized tissues, such as the central nervous system, where the complexity of cell to cell interactions might demand a more rigid membrane structure. We describe here the distribution and induced redistribution of concanavalin A (con A) receptors in the membranes of myelin fragments and synaptosomes studied by immunoferritin electron microscopy.

The anatomy and development of brachypodism in the mouse

Abstract: The autosomal recessive gene for brachypodism ( bp ) in the mouse affects the appendicular, but not the axial skeleton. Manus and pes are more severely affected than the rest of the limbs; the girdles are normal. In digits 2–5, the basal and middle phalanges of the normal are replaced by a short and thin element which never ossifies properly; by contrast, the terminal phalanges are normal or nearly so. Up to the 13-day stage, the limbs of brachypods are externally quite normal, but anomalies of the digital blastemata are detectable in the 12-day embryo already, i.e. before the onset of chondrification. In the 14-day embryo, the overall length of metapod + phalanges is still nearly normal; but the basal and middle phalanges of the normal are represented by a single thin element which is absolutely longer whereas the metacarpale (metatarsale) is correspondingly reduced in length and calibre. This situation is subsequently reversed by heterogonic growth as the phalangeal element of brachypods grows very little. The normality of the terminal phalanges is largely due to the fact that, in the mouse, much of the terminal phalanx is formed directly from membrane and not by replacement of its cartilaginous ‘model’ on which it sits like a thimble. Brachypodism is thus due to an abnormality of the limb blastemata which precedes chondrification, but whose nature is unknown. Generally, muscular and tendinous anomalies parallel those of the skeleton.