Showing papers by "University of Liverpool published in 1983"

The assessment of 210Pb data from sites with varying sediment accumulation rates

Abstract: The last few years have seen a dramatic growth in the use of 210Pb sediment dating. Despite this, considerable doubt still surrounds the nature of the processes by which 210Pb is deposited in lake sediments, and this has lead to a situation where there is a choice of dating models offering different interpretations of 210Pb data. In assessing 210Pb data it is therefore essential to first of all determine whether data is consistent with the assumptions of the dating model, and to then compare the 210Pb chronology with independent dating evidence. We have tested 210Pb data from a wide variety of sites, and our calculations indicate that the crs (constant rate of 210Pb supply) model provides a reasonably accurate chronology when the total 210Pb contents of cores from neighbouring locations are comparable.

Is blindsight an effect of scattered light, spared cortex, and near-threshold vision?

Abstract: Blindsight is the term commonly used to describe visually guided behaviour elicited by a stimulus falling within the scotoma (blind area) caused by a lesion of the striate cortex. Such “vision” is normally held to be unconscious and to be mediated by subcortical pathways involving the superior colliculus. Blindsight is of considerable theoretical importance since it suggests that destriate man is more like destriate monkey than had been previously believed and also because it supports the classical notion of two visual systems. It is also of potential clinical importance, since it has been claimed recently that systematic practice in blindsight can lead to the recovery of normal visual function in patients with cortical lesions. From a review of the literature it is concluded that all of the phenomena of blindsight can be attributed either to light scatter into unimpaired parts of the visual field or to residual vision resulting from spared striate cortex. The possible contribution f other factors is also considered. It is concluded that blindsight studies have generally failed to control for such nonblindsight interpretations partly because of poor methodology and partly because of difficulties in defining the term “blindsight.” Experiments were carried out to investigate the extent to which subjects can exhibit performance similar to blindsight when they are using scattered light as a cue. This was done both with hemianopic subjects (by manipulating the amount of scattered and direct light coming from a stimulus) and with normal subjects (by presenting targets within their blind spots). Good blindsight performance was observed when only scattered light was available as a cue to the subjects. It is therefore concluded that an adequate case for blindsight has not been made. It is probably impossible to demonstrate the existence of blindsight on purely behavioural grounds. What is required is the establishment of relationships between visual function and independent anatomical evidence.

A novel active pentapeptide from chicken brain identified by antibodies to FMRFamide.

Abstract: The tetrapeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) and peptides structurally related to it, have been isolated from molluscan ganglia1–3. They have widespread actions on both invertebrate and vertebrate tissues and there is increasing evidence that they are an important group of invertebrate peptide neurotransmitters3–8. It is of interest that the primary amino acid sequence of FMRFamide forms the C-terminal tetrapeptide of an enkephalin-like heptapeptide (Met-enkephalin-Arg6Phe7) isolated from bovine adrenal medulla and striatum9,10. Antisera to FMRFamide have been shown to react in radioimmunoassay and immunohistochemistry with material in the central nervous system of various vertebrate species11–17, but the identity of this material, and in particular its relationship to the opioid heptapeptide, remains uncertain. We have used antibodies specific for the C-terminus of FMRFamide in radioimmunoassays to monitor purification of the material in chicken brain. We describe here the sequence of one of the peptides obtained. It is a biologically active peptide which does not seem to be related to other known vertebrate neuropeptides.

Voltage and Ca2+-activated K+ channel in baso-lateral acinar cell membranes of mammalian salivary glands

Abstract: Nervous or hormonal stimulation of many exocrine glands evokes release of cellular K+ (ref. 1), as originally demonstrated in mammalian salivary glands2,3, and is associated with a marked increase in membrane conductance1,4,5. We now demonstrate directly, by using the patch-clamp technique6, the existence of a K+ channel with a large conductance localized in the baso-lateral plasma membranes of mouse and rat salivary gland acinar cells. The K+ channel has a conductance of approximately 250 pS in the presence of high K+ solutions on both sides of the membrane. Although mammalian exocrine glands are believed not to possess voltage-activated channels1,7, the probability of opening the salivary gland K+ channel was increased by membrane depolarization. The frequency of channel opening, particularly at higher membrane potentials, was increased markedly by elevating the internal ionized Ca2+ concentration, as previously shown for high-conductance K+ channels from cells of neural origin8-10. The Ca2+ and voltage-activated K+ channel explains the marked cellular K+ release that is characteristically observed when salivary glands are stimulated to secrete.

Surface albedo data for climatic modeling

Abstract: The climate system is driven, primarily, by energy absorbed at the surface. Surface albedo sensitivity is incorporated into all types of climate models, and changes can lead to large feedback effects. For example, alterations in the extent and/or state of the cryosphere and large-scale modification of vegetation cause significant perturbations in climate model results. The specification of surface albedo in general circulation climate models (GCM's) differs. An improved and agreed surface albedo data set is urgently required for climate modeling. It is likely that the most appropriate means of achieving consistent and credible surface albedos is by using well-designed satellite surveillance to augment global inventories of soils and vegetation. However, retrieval of surface albedo values for all sky and surface conditions from satellite observations is difficult. Atmospheric distortion is especially hard to remove. Some of the sensitivity of GCM's to surface albedo values may be the result of inadequate parameterization of other climatic components. The accuracy of information demanded by climate modelers could be reduced and made more consistent. Recommendations are made for the implementation of a new global scale observational program with the aim of providing surface albedo data at an accuracy of ±0.05 within 5–10 years. Immediate initiation is urged.

Quantification of Ca2+-activated K+ channels under hormonal control in pig pancreas acinar cells.

Abstract: Ca2+- and voltage-activated K+ channels are found in many electrically excitable cells and have an important role in regulating electrical activity1–4. Recently, the large K+ channel has been found in the baso-lateral plasma membranes of salivary gland acinar cells, where it may be important in the regulation of salt transport5. Using patch-clamp methods6,7 to record single-channel currents from excised fragments of baso-lateral acinar cell membranes in combination with current recordings from isolated single acinar cells and two- and three-cell clusters, we have now for the first time characterized the K+ channels quantitatively. In pig pancreatic acini there are 25–60 K+ channels per cell with a maximal single channel conductance of about 200 pS. We have quantified the relationship between internal ionized Ca2+ concentration ([Ca2+]i) membrane potential and open-state probability (p) of the K+ channel. By comparing curves obtained from excised patches relating membrane potential to p, at different levels of [Ca2+]i, with similar curves obtained from intact cells, [Ca2+]i in resting acinar cells was found to be between 10−8 and 10−7 M. In microelectrode experiments acetylcholine (ACh), gastrin–cholecystokinin (CCK) as well as bombesin peptides evoked Ca2+-dependent opening of the K+ conductance pathway, resulting in membrane hyperpolarization. The large K+ channel, which is under strict dual control by internal Ca2+ and voltage, may provide a crucial link between hormone-evoked increase in internal Ca2+ concentration and the resulting NaCl-rich fluid secretion5,8.

Clinical pharmacokinetics of oral contraceptive steroids.

Abstract: Oral contraceptive steroids are of 2 types: oestrogens, of which ethinyloestradiol is the most important, and progestagens, of which levonorgestrel and norethisterone are the most commonly used. All these steroids can be measured by a number of analytical techniques but there is little doubt that radioimmunoassay is the most convenient. All the steroids are well absorbed in humans but while levonorgestrel is completely bioavailable, norethisterone has an average bioavailability of 70%. Ethinyloestradiol, too, is subject to presystemic metabolism with a mean bioavailability of 40 to 45%. The main site of presystemic metabolism is the gut wall, with the production of ethinyloestradiol sulphate. The progestagens norethynodrel, ethynodiol diacetate and lynoestrenol are quantitatively metabolised to norethisterone. The pharmacokinetics of the contraceptive steroids are best described by a 2-compartment open model. The terminal plasma half-life of levonorgestrel varies from 11 to 45 hours and of norethisterone from 5 to 14 hours. The β-phase half-life of ethinyloestradiol varies from 6 to 20 hours. The apparent volume of distribution of these contraceptive steroids (after intravenous administration) is between 1.5 and 4.3 L/kg. During long term treatment with oral contraceptive steroids, steady-state plasma concentrations of ethinyloestradiol (24 hours after administration) are between 10 and 200 pg/ml. Plasma concentrations of norethisterone and levonorgestrel at steady-state are higher than predicted from the single-dose kinetics because of enhanced binding of the progestagens following the induction of sex hormone binding globulin (SHBG) by ethinyloestradiol. Concentrations are in the range of 1.6 to 15.2 ng/ml for norethisterone and 0.8 to 4.5 ng/ml for levonorgestrel. All the contraceptive steroids are bound to proteins in plasma. Ethinyloestradiol is 97 to 98% bound to plasma albumin. The progestagens are bound both to albumin (levonorgestrel 93 to 95%; norethisterone 79 to 80%) and more specifically to SHBG. The binding capacity of SHBG can be enhanced by treatment with ethinyloestradiol or with more conventional enzyme-inducing drugs such as phenobarbitone, carbamazepine or rifampicin. Norethisterone and levonorgestrel are chiefly metabolised by reduction in the A ring and this is followed by conjugation with glucuronide or sulphate. The metabolism of levonorgestrel is stereoselective. Ethinyloestradiol is primarily hydroxylated at the 2 position but a wide variety of hydroxylated and methylated metabolites are formed and these are present both free and as glucuronide and sulphate conjugates. Ethinyloestradiol is conjugated directly at the 3 position (unlike the progestagens) and thus is liable to enterohepatic recirculation. Ethinyloestradiol sulphate concentrations in plasma are many times higher than that of the unchanged drug. The oral contraceptive steroids are involved in drug interactions of clinical significance. While the effect of contraceptive steroids on other drugs is small and unlikely to be of clinical significance, failure of contraception often occurs if enzyme-inducing agents such as rifampkin, phenobarbitone or carbamazepine are coadministered. Oral antibiotics do not seem to cause a significant loss of contraception in the large majority of women. Vitamin C will enhance the effect of contraceptive steroids by competing for sulphate conjugation in the gut wall, thus leading to increased bioavailability of ethinyloestradiol.

Identification and probable role of a single neurone containing the neuropeptide Helix FMRFamide.

Abstract: Recently, there has been intense interest in the possibility that peptides might function as neurotransmitters1,2. Despite much progress, there remains no clear-cut example in which the production of a chemically characterized peptide may be ascribed to individual identifiable neurones of proven physiological role/Invertebrate systems have proved to be particularly valuable for the study of identified neurones, including those producing peptides3,4. We have now identified a neurone in ganglia of Helix that is associated with a peptide of the Phe-Met-Arg-Phe-NH2 (FMRFamide) group, and which influences tentacle contraction. This system offers for the first time the capacity to study peptidergic transmission in a system in which both the cell soma and the postsynaptic target may be readily and reproducibly identified.

Themes on circulation in the third world.

Abstract: This article focuses upon circulation, or reciprocal flows of people, with specific reference to Third World societies. The many forms of circulation in Third World societies have lead to a profusi...

A dynamic analysis of spinal compression with different lifting techniques

Abstract: Although it is commonly assumed that lifting with flexed knees and the trunk erect will lead to reduced compressive force on the low back, the benefits are only realized when the load can be lifted between the knees, i.e. close to the body. Moreover, the assumption has often been based solely on an analysis of the initial lifting posture, ignoring the inertial forces due to accelerations of the body and the load. For this study a biomechanical sagittal plane model was developed to take full account of dynamic factors, based on direct recordings of body movements, accelerations of the load and forces at the feet. Twenty subjects lifted a 15 kg box from a 10 cm high shelf to knuckle height with four lifting techniques: leg lift, back lift, load kinetic lift, and trunk kinetic lift. In the ‘kinetic’ lifts the subjects tried to use the kinetic energy of the horizontally moving load or the vertically moving body, respectively, in order to reduce the spinal load. When the peak compressions were considered the l...

Trace fossils formed by heart urchins ‐ a study of Scolicia and related traces

Abstract: Cretaceous and Tertiary traces belonging to the ichnogenera Scolicia, Subphyllochorda and Taphrhelminthopsis are described and analysed functionally. Resting traces continuous with Subphyllochorda are described for the first time and interpreted as the work of heart urchins. The new ichnogenus Cardioichnus is erected for them. The preservation and complexity of some specimens of these ichnogenera allows for a detailed comparison with heart urchin morphology. Subphyllochorda is interpreted as a burrow produced by heart urchins and Scolicia as either burrows or sea floor furrows. The traces here assigned to Taphrhelminthopsis are probably casts of washed-out Subphyllochorda burrows. Palaeozoic traces previously referred to ‘Scolicia’ sensu lato are, in the main, much simpler than the Mesozoic and Tertiary traces and should be transferred to other ichnogenera.

Behavioural tolerance to amphetamine and other psychostimulants: The case for considering behavioural mechanisms

Abstract: An hypothesis is presented about the nature of behavioural tolerance in animals to stimulant drugs. It is suggested that, in many behavioural procedures, tolerance is due to behavioural adaptation to those drug effects which cause disruption of ongoing rewarded behaviour. This unitary hypothesis accounts for the available data on tolerance and cross-tolerance to stimulants more effectively than all of the other more conventional explanations which are based upon dispositional or functional concepts, the most common of which are described, evaluated, and found to be inadequate. Furthermore, it is suggested that attempts to explain tolerance in terms of changes in synaptic functioning are subject to very considerable problems of interpretation and that an analysis of behavioural mechanisms may be of greater value in understanding the process of behavioural tolerance. Evidence for the basic behavioural hypothesis is outlined in some detail, and a theoretical justification presented for its major assumptions. Operant studies of chronic stimulant effects on behaviour have often produced very complex patterns of data, considerable differences being reported both between subjects and between studies. A speculative model is presented which attempts to account for this pattern of data in tolerance studies.

Drug interactions with warfarin.

Abstract: Drugs may interact with warfarin through pharmacodynamic or pharmacokinetic mechanisms. Examples of the former include alteration of the bioavailability of vitamin K by antibiotics, mineral oils or cholestyramine; oestrogens, diuretics and hypolipidaemic agents such as clofibrate may influence vitamin K-dependent clotting factor synthesis, and drugs which affect haemostasis, e.g. via platelet function, will enhance the anticoagulant effect of warfarin. Pharmacokinetic interactions are better understood. Few drugs have been shown to alter warfarin absorption, the importance of protein binding displacement has been exaggerated, and since warfarin is not eliminated to any extent unchanged by the kidney, the most important kinetic interactions are those due to inhibition or induction of its hepatic metabolism. Isomeric differences in metabolism form an important basis for stereoselective metabolic interactions, especially inhibition; this has been demonstrated with phenylbutazone, metronidazole and co-trimoxazole. Enzyme induction, although recognised for many years, may still pose problems in therapeutics, usually on withdrawal of the inducing agent.

The population biology of the Orange Tip butterfly Anthocharis cardamines in Britain

Abstract: . 1 The population biology of Anthocharis cardamines (L.) is described and shown to vary with locality. Southern and Western populations emerge earlier than Northern ones, but Western and Northern populations occupy similar, wetter habitats and are associated primarily with Cardamine pratensis (L.). Southern populations are recorded mostly from Alliaria petiolata (Bieb.). 2 Studies on egg and larval survival indicate that host plant-induced death and parasitization by a tachinid are important mortality factors. However, a key-factor analysis on one population indicates that the major determinant of population size may be the number of eggs laid by ovipositing females, itself dependent upon weather during the oviposition period. Populations in different localities do show similar trends in abundance, corroborating the effect of weather. 3 Human effects on distribution and abundance are discussed, and some conservation strategies suggested.