Showing papers by "Cardiff University published in 1984"

A model of neuronal bursting using three coupled first order differential equations.

Abstract: We describe a modification to our recent model of the action potential which introduces two additional equilibrium points. By using stability analysis we show that one of these equilibrium points is a saddle point from which there are two separatrices which divide the phase plane into two regions. In one region all phase paths approach a limit cycle and in the other all phase paths approach a stable equilibrium point. A consequence of this is that a short depolarizing current pulse will change an initially silent model neuron into one that fires repetitively. Addition of a third equation limits this firing to either an isolated burst or a depolarizing afterpotential. When steady depolarizing current was applied to this model it resulted in periodic bursting. The equations, which were initially developed to explain isolated triggered bursts, therefore provide one of the simplest models of the more general phenomenon of oscillatory burst discharge.

The nature of endothelium-derived vascular relaxant factor

Abstract: The existence of endothelium-derived vascular relaxant factor (EDRF) was postulated by Furchgott and colleagues when they observed that acetylcholine paradoxically relaxed preconstricted aortic strip preparations by an endothelium-dependent mechanism. This phenomenon has since been demonstrated in different blood vessels and mammalian species and it can be elicited by several other agents. EDRF has been thought to be a humoral agent, a lipoxygenase derivative and possibly a free radical. In the study reported here, by using aortic preparations from the rabbit, alone and in cascade experiments with isolated perfused coronary preparations, we demonstrate definitively that EDRF is a humoral agent. It is released from unstimulated aortic preparations containing endothelium, its release can be stimulated for prolonged periods by acetylcholine, and it is not a lipoxygenase derivative or free radical but an unstable compound with a carbonyl group at or near its active site.

The position and topography of the apical canal constriction and apical foramen.

Abstract: . Two hundred and seventy extracted human teeth of unknown age were evaluated for apex to foramen and apex to constriction distances, in addition the topography of the apical portion of the root canal was studied under × 20 magnification. The mean A–F distance was 0.38 mm and the mean A–C distance 0.89 mm, although it must be stressed that a wide range of values was observed. Four distinct types of apical constriction were routinely found, whilst a proportion of canals were apparently blocked. The study confirms the view that it is impossible, with complete certainty, to establish the position of the apical canal constriction during root canal therapy, but indicates that a combination of methods might be more successful than reliance on one.

On the composition of H II regions in southern galaxies. III. NGC 2997 and 7793.

Abstract: On a obtenu des spectres AAT/IPCS pour une partie de la region nucleaire et pour quatre regions HII dans la galaxie SABc NGC 2997, et pour le noyau et cinq regions HII dans la galaxie prototype Sd du groupe Sculptor, NGC 7793. On a deduit les abondances de l'intensite des raies d'emission. On discute des relations qui existent entre les gradients d'abondance et les autres caracteristiques des galaxies spirales

Autoimmune thyroid disease: developments in our understanding.

Abstract: INTRODUCTION THIS REVIEW of autoimmune thyroid disease will highlight the recent advances made in understanding the control of the autoimmune process particularly at pathogenetic and therapeutic levels Many novel techniques have recently been applied to the investigation of thyroid autoimmunity although the results obtained have not always clarified the overall picture These new methodologies are discussed and attention is also focused upon experimental thyroiditis produced in a variety of animals We believe that these models have been neglected somewhat by clinically oriented investigators Yet their use originally led to the foundation of autoimmune concepts, and experimental thyroiditis continues to provide major insights into the possible etiology and pathogenesis of the human counterpart Before discussing thyroid disease in detail however, it is worth considering the current themes in autoimmunity in general

Anthropometric norms in the elderly.

Abstract: Anthropometric indices are presented for representative samples of elderly people in South Wales, based on over 1500 subjects seen during community surveys. Body mass index declined with age after 70 years in both men and women. Estimates of fat and muscle volume based on upper arm measurements also showed a decline with age, which was particularly steep for triceps skinfold thickness in women. These indices are in general similar to results that have been reported from other surveys within the UK; they suggest that Welsh old people have less fat and muscle than elderly Americans.

The strength of the orienting response during Pavlovian conditioning.

Abstract: The strength of orienting toward a light that signaled food was studied in five experiments Experiment 1 demonstrated that this response declined in strength during conditioning but was temporarily restored during extinction In Experiment 2 the light was again paired immediately with the unconditioned stimulus (US), whereas in Experiments 3 and 4 it signaled a tone which in turn signaled the US In these three experiments we again found that continuous reinforcement resulted in a decline in the strength of light orientation These studies also revealed that under conditions of partial reinforcement, orientation to the light was sustained Experiment 5 demonstrated that the decline in light orientation with a continuous reinforcement procedure can be retarded either by preexposing the light for a number of trials prior to conditioning or by intermixing reinforced light trials with nonreinforced presentations of a tone This experiment also revealed that reversing the reinforcement contingency associated with the tone restored orientation to the light This pattern of results can be most readily explained by the proposal that the strength of orientation toward the light is inversely related to the predictive accuracy of this stimulus

A receptor assay for the measurement of TSH receptor antibodies in unextracted serum.

Abstract: SUMMARY A receptor assay for TSH receptor antibodies is described in which unextracted serum, detergent solubilised TSH receptors and 125I-labelled TSH are used. The assay was rapid and reproducible with coefficients of inter-assay variation of 12·3%, 2·1 and 2·6% at mean inhibition of TSH binding values of 11, 53, and 79 respectively. Assay sensitivity could be increased by reducing the volume of receptors used but some increase in the scatter of values obtained with individual normal sera was also observed. Comparison of human and porcine TSH receptor preparations indicated that porcine tissue gave greater sensitivity. Analysis of different groups of patients and normal subjects (n= 21) showed the absence of detectable TSH receptor antibody activity in 16 patients with rheumatoid arthritis, 10 with multinodular goitre and 12 with Hashimoto's disease. However the antibody was readily detectable in 28 out of 28 GRAVES' patients (treated and untreated) who were hyperthyroid at the time of assay.

Evolution and mechanics of a Miocene tidal sandwave

Abstract: A remarkable exposure of Miocene marine molasse in western Switzerland records the evolution of a tidal sandwave over a period of approximately 2 1/2 months. The sandwave is composed of tidal ‘bundles’ in which a sandwave reactivation stage and full vortex stage can be recognized for the dominant flow (ebb tide) and a rippled flood apron overlain by high water drape for the reversed flow. Bundle thicknesses vary systematically through neap–spring cycles, with a periodicity of 27 demonstrating the semi-diurnal lunar control of sedimentation. Waves were an additional component, especially when superimposed on flood tides, producing near-symmetrical combined-flow ripple marks in the flood apron. Tidal current velocities are estimated using critical shear velocities for entrainment, the ripple-dune transition and the dune-plane bed transition. Using appropriate estimates of roughness lengths and a logarithmic velocity law, maximum tidal speeds at 1 m above the bed were approximately 0·6 m sec−1 for ebbs and up to 0·5 m sec−1 for floods. The enhancement by waves of bed shear stress (τwc/τ of approximately 2 for 1 m high waves) under flood currents implies flood tidal velocities closer to 0·2–0·3 m sec−1. Peak instantaneous bedload sediment transport rates using a modified Bagnold equation are nearly 5 times greater under ebb tides than floods. The average net sediment transport rate at springs (0·04 kg m−1 sec−1) is over 10 times greater than at neaps (0·002 kg m−1 sec−1). Comparison with transport rates in modern tidal environments suggests that the marine molasse of Switzerland was deposited under spatially confined and relatively swift tidal flows not dissimilar to those of the present Dutch tidal estuaries.

An investigation into the initial discomfort caused by placement of an archwire

Abstract: Thirty patients completed a discomfort index card for the first 16 days following placement of a fixed appliance. This recorded a score for the degree of discomfort and the analgesic requirement on a sessional basis. It was found that a number of patients suffered severe discomfort over the first few days, 11 scoring at least one severe discomfort session and 12 a moderate discomfort session. The majority of recording occurred over the first 8 days, although the most severe scores were mostly within the first 3 days. Those scoring severe discomfort sessions usually had the worst pain at night, and this correlated well with when analgesics were most required. Those patients scoring at most mild discomfort (5) had this discomfort evenly distributed throughout the day. There was a statistically significant difference in the discomfort experience of adolescents under 16 years of age and adults over 16 years of age.

Evidence for an effect of antithyroid drugs on the natural history of graves' disease

Abstract: In the United Kingdom, about half the patients with Graves' disease who are given antithyroid drugs are still in remission one year after treatment is stopped. The most widely held view is that such remission rates are due only to the biochemical effects of the drugs, the disease either spontaneously remitting or abating when the immune system is no longer subject to the stimulatory effects of excessive thyroid hormone. We review here the accumulating evidence against both of these alternatives. In contrast, there is now a large body of work which shows that thyrotrophin receptor antibody levels, central to the aetiology of Graves' hyperthyroidism, fall during antithyroid treatment and that remission may be related to this fall in a fashion which is dependent on the dose and duration of treatment. This immunosuppressive effect is supported by experimental data and on the basis of these results we propose that antithyroid drugs may modify the natural history of Graves' disease and contribute to the remission which occurs in a proportion of treated patients.

Petrology and geochemistry of lower to middle Ordovician igneous rocks in Wales: a volcanic arc to marginal basin transition

Abstract: Volcanic activity was widespread in Wales during Ordovician times. There are marked petrological and geochemical differences between late Tremadoc volcanism and that of Arenig to Llandeilo age. The earlier activity, represented by the Rhobell Volcanic Complex and the Trefgarn Volcanic Group, comprises a fractionation continuum which is basalt-andesite-dacite-rhyodacite and is similar to that of modern volcanic arcs. In contrast, the later activity, as seen in the Fishguard Volcanic Complex and the Aran Volcanic Group, is represented by basalt-rhyolite bimodal sequences. The basic rocks are similar to those of ensialic marginal basins and the acidic magmas were most probably generated by crustal fusion. The contemporaneous Builth Volcanic Group has some arc-like characteristics but the variation is here interpreted as due to the influence of subduction zone components in marginal basin magma generation. The change from the Tremadoc to later volcanism reflects an arc to marginal basin transition.

The deleterious effects of myocardial catecholamines on cellular electrophsiology and arrhythmias during ischaemia and reperfusion

Abstract: Action potentials and ECGs were recorded from Langendorff perfused guinea pig hearts during ischaemia and reperfusion. Arrhythmias were significantly more frequent during low flow (10% of control) than zero flow ischaemia and were most frequent during reperfusion following 30 minute ischaemia. Arrhythmias during low flow ischaemia were preceded by spontaneous recovery in action potential amplitude and Vmax and marked shortening of refractory period which did not occur during zero flow ischaemia. Reperfusion VF was always preceded by further shortening of the action potential. Myocardial catecholamine depletion, by pre-treatment with 6-hydroxydopamine significantly reduced the incidence of arrhythmias during ischaemia and reperfusion. Catecholamine depletion blunted the ischaemia-induced reduction in action potential amplitude and Vmax, prevented any spontaneous recovery and abolished reperfusion induced shortening of action potential duration. Methoxamine given to catecholamine-depleted hearts, having only minor effects during normal perfusion, significantly reversed the anti-arrhythmic and electrophysiological effects of catecholamine depletion during ischaemia and reperfusion. Phentolamine and propranolol in anti-arrhythmic concentrations, profoundly modified the electrophysiological effects of ischaemia and reperfusion. These results suggest that release of endogenous myocardial catecholamines contributes through alpha and beta-adrenoceptor stimulation to the electrophysiological changes and arrhythmias during myocardial ischaemia and reperfusion.

Ultimate capacity of uniaxially compressed perforated plates

Abstract: An approximate method of predicting the ultimate load carrying capacity and the post-buckling behaviour of perforated plates typically used in engineering structures is presented. The theory is based on a mechanism solution, used in conjunction with an elastic loading path derived from energy methods. Experiments have shown that a good approximation of the loading and unloading paths for simply supported plates containing square and circular openings has been obtained by the suggested theoretical treatment. Curves suitable for the use of designers have been proposed and can be employed to determine the ultimate capacity of approximately square plates containing centrally placed holes.

Comparison of the immediate effects on the sub‐gingival microflora of acrylic strips containing 40% chlorhexidine, metronidazole or tetracycline

Abstract: In the management of chronic periodontitis, there has been a renewed interest in the local delivery of antimicrobial drugs into periodontal pockets. This study assessed the effects of the acrylic strip delivery system containing chlorhexidine, metronidazole or tetracycline on subgingival microflora assessed by dark field microscopy. Strips containing 40% chlorhexidine, metronidazole or tetracycline were placed for 2 to 3 days into pockets greater than 6 mm which bled on probing. Plaque samples were obtained before and after treatment and counts of morphological and motile groups of organisms were made by dark field microscopy. Prior to treatment, the dark field microscopic counts were similar to those previously reported for diseased sites with motile bacteria, in particular spirochaetes, present in high numbers. Following treatment, all 3 antimicrobial drugs produced a significant increase in the proportion of cocci and significant decreases in all other types of organisms. Motile organisms, in particular, were markedly reduced and spirochaetes could not be recovered from some sites treated with metronidazole and tetracycline. Metronidazole was significantly more effective than tetracycline or chlorhexidine on spirochaetes. The results indicate that acrylic strips may be useful in the management of chronic periodontitis as an adjunct to routine mechanical methods.