Showing papers by "Cardiff University published in 1987"

A model for stimulus generalization in Pavlovian conditioning.

Abstract: A selective review of experiments that can be said to demonstrate the effects of generalization decrement in Pavlovian condition is presented, and it is argued that an adequate theoretical explanation for them is currently not available. This article then develops a theoretical account for the processes of generalization and generalization decrement in Pavlovian conditioning. It assumes that animals represent their environment by a stimulus array in a buffer and that this array in its entirety constitutes the conditioned stimulus. Generalization is then held to occur whenever at least some of the stimuli represented in the array on a test trial are the same as at least some of those represented in the array during training. Specifically, the magnitude of generalization is determined by the proportion of the array occupied by these common stimuli during training compared to the proportion of the array they occupy during testing. By adding to this principle rules concerning excitatory and inhibitory learning, it is proposed, the model can explain all the results that were difficult for its predecessors to account for. A fundamental property of conditioned responding is that it may occur in circumstances that differ from those prevailing during acquisition. This phenomenon is referred to as generalization, and the term generalization decrement is used when this transfer is less than complete. These effects have been revealed with both Pavlovian and instrumental conditioning, using a variety of species and a wide range of conditioned stimuli (CS) and unconditioned stimuli (US). As iar as instrumental conditioning is concerned, a considerable number of studies have been directed at examining the factors that influence the magnitude of generalization from one situation to another (for reviews see Honig & Urcuioli, 1981; Mackintosh, 1974). These results also have been the focus of considerable theoretical analysis. In contrast, much less attention has been paid to the role of generalization in Pavlovian conditioning. Only a few studies have been concerned specifically with demonstrating the generalization decrement of a Pavlovian conditioned response (CR) as a result of modifying the properties of the CS (Hofiman & Fleshier, 1961; Hovland, 1937; Moore, 1972; Pavlov, 1927; Siegel, Hearst, George, & O'Neal, 1968). Furthermore, only a few theorists have been specifically concerned with the analysis of these and related effects (Hull, 1943; Pavlov, 1927). An alternative approach has been to show how a particular theoretical analysis of the Pavlovian learning process can be extended to account for generalization and generalization decrement (cf. Rescorla, 1976). The argument presented in this article is based on the premise that an adequate account for the effects of generalization must lie at the core of

Epidemiological and environmental evidence of the health effects of exposure to erionite fibres: a four-year study in the cappadocian region of Turkey

Abstract: An environmental and epidemiological study has been carried out in Central Cappadocia, Turkey, aiming at investigating the relationship between exposure to naturally occurring erionite fibres and the reported high incidence of malignant mesotheliomas. Airborne fibre levels are generally low but show a higher proportion of erionite fibres in the villages affected by malignant disease than in a control village. The same pattern is confirmed by analysis of the fibre content in lung tissues of sheep from several villages, both affected and unaffected by malignant disease. The 3 villages with the highest proportion of erionite fibres have high rates of malignant pleural mesothelioma, malignant peritoneal mesothelioma and lung cancer. No case of malignancy for the same sites has been reported during the study period from the control village. The relationships between these findings and their consistency with the results from experimental studies indicate erionite fibres as a carcinogenic agent, although some aspects of the exposure are not fully clarified.

Free fatty acids block growth hormone (GH) releasing hormone-stimulated GH secretion in man directly at the pituitary.

Abstract: Increases in plasma FFA levels inhibit GH responses to a variety of pharmacological and physiological stimuli. To gain further insight into the mechanism by which FFA exert their effect, we studied the plasma GH responses to GHRH-(1-44) (1 microgram/kg, iv) in normal subjects in whom plasma FFA levels were raised by a lipid-heparin infusion (250 mL 10% Intralipid plus 2500 U heparin). Paired tests were performed in 10 normal subjects, with and without lipid-heparin pretreatment. Lipid-heparin infusion from -30 to 120 min increased mean FFA levels from 0.41 +/- 0.03 (+/- SEM) to 3.12 +/- 0.40 mmol/L at 120 min. The mean plasma GH levels after GHRH administration were lower at all times; however, the values were significantly different (P less than 0.05) only at the later times (45, 60, and 90 min). When considered individually, an all or none pattern was observed; 5 subjects had no plasma GH response to GHRH, and 5 had no reduction. To investigate the time relationships between the FFA peak and subsequent GH blockade, a different protocol of paired tests was performed with GHRH with or without a different lipid-heparin infusion protocol. Lipid-heparin was infused from -90 to 0 min, with an additional heparin pulse at -15 min, to obtain a higher and earlier (0 min) FFA increase. FFA increased from 1.06 +/- 0.19 to 11.61 +/- 0.83 mmol/L at zero time. The GHRH-induced GH secretory peak (15.8 +/- 3.5 ng/ml) at 15 min was completely blocked (0.9 +/- 0.2 ng/ml), and the mean plasma GH levels were also lower at 30, 45, and 60 min. To determine whether the FFA-induced blockade of GH secretion was exerted in the pituitary, a series of in vitro studies was conducted using monolayer cultures of rat anterior pituitary glands, with GHRH concentrations of both 10(-10) and 10(-8) M and 10(-5) M forskolin to stimulate GH release. Both caprylic and oleic acid inhibited basal GH release and GHRH- or forskolin-induced GH release. PRL release was not altered, nor were toxic actions noted on the cells. In conclusion, FFA are able to block GH secretion directly at the pituitary level.

Persistence of bacterial denitrification capacity under aerobic conditions: The rule rather than the exception

Abstract: Bacterial decomposition of nitrate to dinitrogen and oxides of nitrogen, essential steps in the nitrogen cycle, are regarded as predominantly anaerobic processes. However, here we have shown, using simultaneous mass spectrometric monitoring of dissolved N2, NOx and O2, that in the laboratory a number of different bacteria can denitrify, even when O2 concentrations approach or exceed air saturation values. The proportions of gaseous end products vary from one organism to another and depend on the level of dissolved O2. We, therefore, suggest that aerobic bacterial denitrification, with the production of N2 and/or NOx, may, contrary to the beliefs of many, be as widespread and ecologically important as its anaerobic counterpart.

Sex hormones, insulin, lipids, and prevalent ischemic heart disease

Abstract: The relations between estradiol, testosterone, insulin, lipids, and prevalent ischemic heart disease were examined using the cross-sectional data from the Caerphilly Heart Disease Study, a cohort of 2,512 men (aged 45-59 years) surveyed between 1978 and 1982. Endogenous levels of estradiol were associated directly with high density lipoprotein (HDL) cholesterol (r = 0.106, p less than 0.001), but this relation was removed after adjustment for testosterone and insulin levels. Estradiol was not associated with prevalent ischemic heart disease. Endogenous levels of testosterone were associated directly with HDL cholesterol (r = 0.148, p less than 0.001) and inversely with triglyceride (r = -0.217, p less than 0.001). Persons with prevalent ischemic heart disease had significantly lower testosterone levels than persons without ischemic heart disease (mean levels 20.9 vs. 22.0 nmol/liter, p less than 0.01). These relations were confounded by associations with insulin. The associations between testosterone and the lipids persist after adjusting for body mass index, age, and insulin. The association between testosterone and prevalent ischemic heart disease was reduced after adjusting for insulin and/or triglyceride levels. The results suggest that insulin and testosterone may have an interdependent regulatory effect on lipid metabolism. The effect of testosterone on ischemic heart disease appears to be primarily mediated through its association with insulin. Future work on sex hormones and ischemic heart disease will need to account for the effects of insulin.

Comparative studies of plant growth and distribution in relation to waterlogging

Abstract: Summary Rooted cuttings of Salix caprea L. and -S. cinerea ssp. oleifolia (Macreight) growing in soil were exposed to (a) intermittent, (b) partial and (c) complete waterlogging of the soil. Measurements of growth and other characteristics were compared with unflooded controls. Both species were harmed by waterlogging but S. caprea was more sensitive than 5. cinerea as shown by the greater reduction of height, internode number, dry weight of root, stem and leaf, specific leaf area and leaf area per plant. The waterlogging treatments did not differ amongst themselves in the degree of inhibition of growth which they caused. A single fully waterlogged treatment would thus have been quite adequate in screening for tolerance. The reduction in specific leaf area of S. caprea was probably mediated by reduced turgidity and failure of leaf tissue to expand fully. Leaf iron content increased in both species but less so in S. cinerea, which is able to immobilize more iron in, or on, its roots. 5. caprea leaves contained over 2000 μg g−1 iron, a concentration recorded as toxic in other plants; these leaves became brittle and some lower leaves were shed. Root iron content increased more in S. cinerea than in S. caprea, and this was accompanied by an increase in phosphorus content. Chlorophyll and magnesium content of leaves was significantly reduced in S caprea but not in S. cinerea. Photosynthetic potential was reduced in S. caprea but not in S. cinerea; this was probably unrelated to stomatal control of CO2 uptake. S. cinerea produced adventitious roots at the surface of flooded soil and when cuttings were immersed in water; S. caprea did not. These observations are compatible with the ecology of the two species, S. caprea normally inhabiting better drained soils than 51. cinerea.

High resolution X-ray analyses of renin inhibitor-aspartic proteinase complexes

Abstract: Inhibitors of the conversion of angiotensinogen to the vasoconstrictor angiotensin II have considerable value as antihypertensive agents. For example, captopril and enalapril are clinically useful as inhibitors of angiotensin-converting enzyme. This has encouraged intense activity in the development of inhibitors of kidney renin, which is a very specific aspartic proteinase catalysing the first and rate limiting step in the conversion of angiotensinogen to angiotensin II. The most effective inhibitors such as H-142 and L-363,564 have used non-hydrolysable analogues of the proposed transition state, and partial sequences of angiotensinogen (Table 1). H-142 is effective in lowering blood pressure in humans but has no significant effect on other aspartic proteinases such as pepsin in the human body (Table 1). At present there are no crystal structures available for human or mouse renins although three-dimensional models demonstrate close structural similarity to other spartic proteinases. We have therefore determined by X-ray analysis the three-dimensional structures of H-142 and L-363,564 complexed with the aspartic proteinase endothiapepsin, which binds these inhibitors with affinities not greatly different from those measured against human renin (Table 1). The structures of these complexes and of that between endothiapepsin and the general aspartic proteinase inhibitor, H-256 (Table 1) define the common hydrogen bonding schemes that allow subtle differences in side-chain orientations and in the positions of the transition state analogues with respect to the active-site aspartates.

Some long term effects of smoking on the haemostatic system: a report from the Caerphilly and Speedwell Collaborative Surveys.

Abstract: Data from two community studies on men from South Wales and the west of England suggest that the effects of smoking on the haemostatic system remain for many years after giving up. Long term correlations between several variables, including plasma fibrinogen and white cell count, and the length of time after giving up were seen in ex-smokers. Dose response relations were apparent in current smokers in terms of the white cell count and two haematological variables, the packed and mean cell volumes. These long term correlations probably reflect the toxicity of other agents in tobacco smoke besides nicotine and carbon monoxide, which act only in the short term. Identification of these agents may further our understanding of the mechanism by which cigarette smoking is associated with atherosclerotic disease.

Isolation, biochemical characterization, and culture of lung type II cells of the rat.

Abstract: A method is described for the isolation of rat lung epithelial Type II cells using trypsin digestion of tissue to release cells for subsequent separation by Percoll gradient centrifugation. Both the concentration of trypsin and the age (body weight) of the rat affect the yield from primary digestion and the final number of Type II cells obtained. A lung weighing 1 g from a 200 g rat yields approximately 30 X 10(6) washed Type II cells (approximately 25% of the total estimated lung population). These cells have a plating efficiency of 40-50% after 48 h of culture. The cells have a high alkaline to acid phosphatase ratio (usually greater than 4.0) compared with that of alveolar macrophages (0.1) and accumulate putrescine by an active transport mechanism with an apparent KM between 8 and 14 microM. Together with studies of [3H]thymidine uptake into DNA, which is maximal between 48 and 72 h of culture, these quantitative measurements form a good basis for investigating the interactions between a number of chemical agents and Type II cells in vitro.

The complications of colposuspension

Abstract: Fifty patients with stress incontinence treated by a colposuspension procedure were reviewed symptomatically and urodynamically before and after surgery and followed up for 1 to 6 years (mean 4.5). Although 84% were continent post-operatively, only 63% of those previously operated on for incontinence were dry, and only 44% were dry and complication-free in the long term.

Excitatory amino acid receptors and synaptic transmission in the rat ventrobasal thalamus.

Abstract: 1 Extracellular single-neurone recordings were made in the ventrobasal thalamus (vbt) of urethane-anaesthetized rats with multi-barrel ionophoretic electrodes in order to test the hypothesis that excitatory amino acid receptors are involved in the responses of these neurones to stimulation of sensory afferents 2 Responses of neurones to either physiological stimulation of hair and vibrissa follicle sensory afferents and to ionophoretically applied excitatory amino acids were challenged with the antagonists D-2-amino-5-phosphonovalerate (APV), kynurenate and gamma-D-glutamylaminomethyl sulphonate (GAMS) 3 In agreement with previous findings in other brain areas, ionophoretically applied APV was found to selectively antagonize responses of vbt neurones to N-methylaspartate (NMA), whereas GAMS was found to be moderately kainate selective Kynurenate was found to be relatively non-selective 4 Responses of neurones to short-duration (10-20 ms) physiological stimulation of afferents were resistant to APV when this antagonist was applied with NMA-selective ionophoretic currents In contrast, these APV currents were adequate to antagonize responses to maintained physiological stimulation 5 The broad spectrum excitatory amino acid antagonist kynurenate was found to block synaptic responses of vbt neurones to both short-duration and maintained stimuli when it was applied with currents which were sufficient to reduce responses to ionophoretic quisqualate 6 GAMS was found to selectively block kainate responses in a proportion of the neurones tested In such cases, there was little effect of the antagonist on the responses evoked by either short-duration or maintained sensory stimuli 7 It is concluded that excitatory amino acid receptors of both the NMDA and non-NMDA type are involved in the synaptic responses of vbt neurones to sensory afferent stimulation, and that the apparent synaptic pharmacology depends on the mode of stimulation of the afferent pathway

The Marketing Budgeting Process: Marketing Management Implications:

Abstract: Most examinations of marketing and advertising budgeting concentrate on techniques ranging from arbitrary “rules of thumb” to complex management science models. The author suggests greater insight ...

Coalescing binaries—Probe of the universe

Abstract: At present, coalescing binary systems containing neutron stars or black holes are thought to be the most likely sources of gravitational waves to be detected by long baseline interferometers being currently designed. In this essay we calculate the characteristics of the signal from a coalescing binary to the first post-Newtonian order. We show that at coalescence the eccentricity of the orbit, tidal effects, and magnetic interactions can be neglected. We also consider the effects of the expansion of the universe on the signal. We show that observations of gravitational waves from coalescing binaries by a network of detectors will provide a wealth of astrophysical information, e.g., determination of the Hubble constant, new rungs on the cosmic distance ladder, estimates of the masses of components of the binary systems, information about the mass distribution in the universe, highly accurate tests of general relativity, and constraints on neutron-star equations of state. Further development of laser interferometers may enable determination of the deceleration parameter, provide new information about evolution of the universe, and even enable observation of such effects as gravitational lensing.

Introduction to animal cognition

Abstract: The study of animal cognition the representation of knowledge memory processes associative learning attention the translation of knowledge into action problem solving and reasoning communication and language.

The distribution of plaque and gingivitis and the influence of toothbrushing hand in a group of South Wales 11-12 year-old children.

Abstract: Numerous factors may affect the distribution of plaque and gingivitis in any individuals mouth. Of considerable importance must be the oral hygiene habits of each person, which will be influenced by compliance and dexterity with tooth cleaning methods. The pattern of gingivitis seen at a young age may, with time, reflect the eventual distribution of attachment loss. This in part, could explain the considerable variation in chronic periodontal disease seen between individuals and at different sites within the same mouth. This study reports the baseline data for the distribution of plaque and gingivitis in 1105, 11-12-year-old children in South Wales. The children were selected by disproportionate stratified random sampling and examined by a multidisciplinary group with the long-term aim of evaluating the importance of malocclusion to dental health and psychosocial variables. Toothbrushing frequency had a very low but significant correlation with the distribution of plaque and gingivitis, accounting therefore for only a small % of the variance in the group. For the total group and right-handed toothbrushers, buccal plaque and gingivitis was significantly increased on right contralateral teeth. No specific pattern for plaque and gingivitis distribution by side was seen for 100 left-handed toothbrushers. Plaque and gingivitis also showed significant differences dependent upon arch, tooth number, and surface. The population is being followed at 4-year intervals to monitor the pattern of periodontal disease with time and correlate changes with these baseline findings.

Is asthma increasing

Abstract: Asthma mortality is again causing concern. An epidemic of deaths occurred in several countries among young people during the 1960s. In Britain, asthma mortality became higher than it had been at any time in the previous hundred years, throughout which it had been fairly stable.' The epidemic subsided, and by 1974 the death rate had returned to its previous level. In view of the advances in treatment and management since the 1950s it might have been expected that mortality would now be well below pre-epidemic rates. But, in fact, the death rate during the later 1970s remained at about the same level as before. Currently it is showing an alarming tendency to drift upwards again (fig 1). What is going wrong? International comparisons reveal some striking differences in the pattern ofasthma mortality. Caution is obviously required in comparing data from different countries which may use different diagnostic criteria. Death rates among children and young adults are least liable to diagnostic confusion, however, since in this age group the mortality from acute and chronic bronchitis is very low. It appears to be a fact that the epidemic in the 1960s occurred in some countries (eg, Britain, Ireland, Australia, New Zealand and Norway) but not in others (eg, the United States, Canada, Belgium, and West Germany).2 It was noticed that the countries affected had licensed the use ofpressurised aerosols containing high concentrations of sympathomimetic amines, and this led to the suggestion that over use of these drugs had caused the excess mortality.3 This explanation has since been challenged, however, 4 5 and the issue continues to be debated. The present rise in mortality is not occurring in all countries. New Zealand seems to have experienced a particularly sharp rise since 1975, and death rates there are now even higher than they were during the previous epidemic.6 American and Canadian rates have been remarkably low and stable for many years,6 although among children under 14 years of age there has been a recent tendency for asthma deaths to rise in the United States from 1.0 per million in 1977 to 2.2 per million in 1983.7 West Germany, which was also ICD I ICD ' ICD 7th revision 8th revision 9th revision

Vestibular and optokinetic eye movements evoked in the cat by rotation about a tilted axis

Abstract: Horizontal and vertical eye movements were recorded from cats in response to either a) off-vertical axis rotation (OVAR) at a range of velocities (5–72 deg/s) and a range of tilts (0–60 deg) or b) horizontal (with respect to the cat) optokinetic stimulation (10–80 deg/s), also around a range of tilted axes (0–60 deg). The responses to stopping either of these stimuli were also measured: post-rotatory nystagmus (PRN) following actual rotation, and optokinetic after nystagmus (OKAN) following optokinetic stimulation. The response found during OVAR was a nystagmus with a bias slow-phase velocity that was sinusoidally modulated. The bias was dependent on the tilt and reached 50% of its maximum velocity (maximum was 73±23% of the table velocity) at a tilt of 16 deg. The phase of modulation in horizontal eye velocity bore no consistent relation to the angular rotation. The amplitude of this modulation was roughly correlated with the bias with a slope of 0.13 (deg/s) modulation/(deg/s) bias velocity. There was also a low-velocity vertical bias with the slow-phases upwardly directed. The vertical bias was also modulated and the amplitude depended on the bias velocity (0.27 (deg/s) modulation/ (deg/s) bias velocity). When separated from the canal dependent response, the build up of the OVAR response had a time constant of 5.0±0.8 s. Following OVAR there was no decline in the time constant of PRN which remained at the value measured during earth-vertical axis rotation (EVAR) (6.3±2 s). The peak amplitude of PRN was reduced, dependent on the tilt, reaching only 20% of its EVAR value for a tilt of 20 deg. When a measurable PRN was found, it was accompanied by a slowly-emerging vertical component (time constant 5.4±2s) the effect of which was to vector the PRN accurately onto the earth horizontal. OKN measured about a tilted axis showed no differences in magnitude or direction from EVAR OKN even for tilts as large as 60 deg. OKAN following optokinetic stimulation around a tilted axis appeared normal in the horizontal plane (with respect to the animal) but was accompanied by a slowly emerging (time constant 4.1±2 s) vertical component, the effect of which was to vector the overall OKAN response onto the earth horizontal for tilts less than 20 deg. These results are compared with data from monkey and man and discussed in terms of the involvement of the velocity storage mechanism.

The lipid composition and permeability to azole of an azole- and polyene-resistant mutant of Candida albicans

Abstract: Candida albicans 6.4, which is resistant to both polyene and azole groups of antifungal antibiotics, has a larger lipid content and lower polar lipid to neutral lipid ratio compared with other strains that are sensitive or resistant only to azoles. C. albicans 6.4 contains a relatively greater proportion of triacylglycerol in its neutral lipid in the exponential phase of batch culture compared with other strains, but, unlike them, does not accumulate triacylglycerols or any other stored lipid in the stationary phase. Like other strains, in C. albicans 6.4 the major phospholipids are phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, but sphingomyelin is absent; the major fatty acids are palmitic, palmitoleic, oleic and linoleic acids. In common with other C. albicans strains, strain 6.4 contains non-specific (lyso)phospholipase activity. The main distinctive feature of the lipid composition of C. albicans 6.4 is the absence of ergosterol, which is replaced by methylated sterol; mainly lanosterol, 24-methylene-24,25-dihydrolanosterol and 4-methylergostadiene-3-ol. It is suggested that the altered membrane sterol pattern provides a common basis for the double resistance by preventing polyene binding and reducing azole permeability.

Hydrogen-dependent control of the continuous anaerobic digestion process

Abstract: Membrane inlet mass spectrometry was used to directly measure the concentrations of CH4 and H2 in a mesophilic (37°C) completely mixed, laboratory scale, anaerobic digester, continuously fed at a retention time of 7 days with a glucose (50 mM) mineral salts medium. When the digester was overloaded by an increase in the influent substrate concentration, equivalent to 15.5 kg (COD) m-3 (digester) day-1 the concentrations of H2 and short chain fatty acids increased with a concomitant decline in the pH: following an initial stimulation methanogenesis was inhibited. Regulation of the H2 signal from the mass spectrometer in a closed feedback loop by controlled addition of carbon source under a potential overload condition, enabled the H2 concentration to the controlled around 1μM and a high steady state rate of methanogenesis of 42 μM min-1 to be maintained; this is equivalent to 1.4 volumes of CH4 per culture volume per day. The hydrogen-dependent control system was also used to prevent inhibition of methanogenesis when the digester was subject to volumetric overloading potentially equivalent to a retention time of 1 day.