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Biomedical subjects

C Fyfe

Publications and source records attributed to C Fyfe.

9 recordsLinked to original sources
PubMed1999

Dexamethasone effects on cerebral protein synthesis prior to and following hypoxia-ischemia in immature rat.

We hypothesized that the neuroprotection against cerebral hypoxic-ischemic damage observed with dexamethasone treatment in immature rats is related to a change in cerebral protein synthesis. Six-day-old Wistar rats were injected with either vehicle (10 ml/kg) or dexamethasone (0.1 mg/kg) 24 h prior to cerebral hypoxia-ischemia. Local cerebral protein synthesis (incorporation of 14C-leucine into proteins) was measured in 7-day-old rats during normoxia, during hypoxia-ischemia, and after hypoxia-ischemia which was produced with right carotid artery ligation and 2-h exposure to 8% O2. In normoxic controls, cerebral protein synthesis was similar in dexamethasone and vehicle-treated animals. During hypoxia-ischemia, local cerebral protein synthesis decreased markedly (p < 0.0001) in ischemic regions ipsilateral to the occlusion, irrespective of treatment. After hypoxia-ischemia, protein synthesis declined even further in vehicle-treated animals. Reductions in protein synthesis were substantially more severe in vehicle- than dexamethasone-treated animals, particularly after hypoxia-ischemia (p < 0.0001). Thus, neuroprotection with dexamethasone is not related to a reduction in basal levels of cerebral protein synthesis, but is associated with an improved protein synthesis during and following hypoxia-ischemia.

Animals↗
PubMed1998

Modelling multiple-cause structure using rectification constraints.

We present an artificial neural network which self-organizes in an unsupervised manner to form a sparse distributed representation of the underlying causes in data sets. This coding is achieved by introducing several rectification constraints to a PCA network, based on our prior beliefs about the data. Through experimentation we investigate the relative performance of these rectifications on the weights and/or outputs of the network. We find that use of an exponential function on the output to the network is most reliable in discovering all the causes in data sets even when the input data are strongly corrupted by random noise. Preprocessing our inputs to achieve unit variance on each is very effective in helping us to discover all underlying causes when the power on each cause is variable. Our resulting network methodologies are straightforward yet extremely robust over many trials.

Animals↗
PubMed1995

Introducing asymmetry into interneuron learning.

A review is given of a new artificial neural network architecture in which the weights converge to the principal component subspace. The weights learn by only simple Hebbian learning yet require no clipping, normalization or weight decay. The net self-organizes using negative feedback of activation from a set of "interneurons" to the input neurons. By allowing this negative feedback from the interneurons to act on other interneurons we can introduce the necessary asymmetry to cause convergence to the actual principal components. Simulations and analysis confirm such convergence.

Interneurons↗
PubMed1994

Serum lipid profile determines platelet reactivity to native and modified LDL-cholesterol in humans.

The effects of thrombin (0.2 U/ml) and native (n-LDL), malondialdehyde-modified (MDA-LDL) and auto-oxidized (ox-LDL) low-density lipoproteins (20 micrograms of protein/ml) on platelet activation were evaluated in seven hyperlipidemic patients and compared to seven controls (fasting serum cholesterol 8.49 +/- 0.5 and 4.61 +/- 0.4 mM, respectively). Basal and thrombin-induced increases in platelet intracellular free calcium ion concentration ([Ca2+]i; fura-2) were similar in hyperlipidemic patients and controls (45 +/- 5 vs 42 +/- 3 and 635 +/- 51 vs 599 +/- 69 mM, respectively). n-LDL, MDA-LDL and ox-LDL increased basal [Ca2+]i (16, 36 and 81 percent, p < 0.01 between LDL-types), increases were consistently smaller in patients. There was an inverse relationship between LDL-induced responses and fasting serum LDL cholesterol as well as LDL/HDL ratio. In conclusion, modified LDL activated platelets to a greater extent than n-LDL, suggesting different types of LDL-receptors. Their agonistic effect was inversely related to the fasting serum lipid profile, suggesting that blunting of platelet responses to LDL could represent a protective mechanism in hyperlipidemic patients.

Adult↗
PubMed1990

Investigations of the horse conceptus via magnetic resonance imaging (MRI) and nitroxide spin labels as contrast agents.

Results are presented which illustrate the usefulness of Magnetic Resonance Imaging as applied to the study of living embryos. Nitroxide spin labels were employed as contrast agents to study the structure and properties of the embryos. These spin labels offer the additional advantage that they may potentially be bound to biologically important molecules thereby imparting the ability to produce contrast in the MR images to these new molecules. The horse conceptus was chosen over other embryos due to its large size. Whereas the embryos of cattle and swine are sub-millimetre in size, the horse conceptus is on the order of 10 millimetres in diameter. The availability of microscopic imaging gradient coils will allow the techniques developed in this study to be applied to the smaller embryos of other species.

Animals↗
PubMed1986

A simple adjustable functional brace for tibial fractures.

The use of an adjustable functional brace for fractures of the tibia has several practical and theoretical advantages. The high cost of commercially available braces has limited their use until now. We describe a simple, inexpensive orthosis which has given good results in a clinical study for 32 unselected fractures. The fractures' alignment was well maintained. The brace was comfortable to wear and there were few complications. It is hoped that the low cost of this simple custom-made brace will encourage more widespread use of this technique.

Adolescent↗
PubMed1982

An integrative approach to the electrophoresis of the reductase and dehydrogenase isozymes in respiring and fermenting yeasts.

A method is described for qualitatively monitoring changes in the starch gel electrophoresis isozyme patterns of key yeast dehydrogenase and reductase activities involved in the transition from aerobic to anaerobic conditions during batch fermentations. The hypoxic transition was accompanied by the disappearance of catalase, superoxide dismutase, mitochondrial dehydrogenases and the appearance of a novel 6-phosphogluconic acid dehydrogenase activity. Significant genetic differences were noted in the banding patterns of wine yeasts, baker's yeast and a commonly used laboratory yeast strain.

Alcohol Oxidoreductases↗
PubMedDate not supplied

Stochastic ICA contrast maximisation using OJA's nonlinear PCA algorithm.

Independent Component Analysis (ICA) is an important extension of linear Principal Component Analysis (PCA). PCA performs a data transformation to provide independence to second order, that is, decorrelation. ICA transforms data to provide approximate independence up to and beyond second order yielding transformed data with fully factorable probability densities. The linear ICA transformation has been applied to the classical statistical signal-processing problem of Blind Separation of Sources (BSS), that is, separating unknown original source signals from a mixture whose mode of mixing is undetermined. In this paper it is shown that Oja's Nonlinear PCA algorithm performs a general stochastic online adaptive ICA. This analysis is corroborated with three simulations. The first separates unknown mixtures of original natural images, which have sub-Gaussian densities, the second separates linear mixtures of natural speech whose densities are super-Gaussian. Finally unknown mixtures of original images, which have both sub- and super-Gaussian densities are separated.

Algorithms↗