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Biomedical subjects

L R Williams

Publications and source records attributed to L R Williams.

At least 19 recordsLinked to original sources
PubMed2001

Orientation, scale, and discontinuity as emergent properties of illusory contour shape.

A recent neural model of illusory contour formation is based on a distribution of natural shapes traced by particles moving with constant speed in directions given by Brownian motions. The input to that model consists of pairs of position and direction constraints, and the output consists of the distribution of contours joining all such pairs. In general, these contours will not be closed, and their distribution will not be scale-invariant. In this article, we show how to compute a scale-invariant distribution of closed contours given position constraints alone and use this result to explain a well-known illusory contour effect.

Animals↗
PubMed2001

Coincidence timing of finger, arm, and whole body movements.

Two experiments investigated the effects of different types of movement responses on coincidence timing skill. The view was taken that the sensory-motor integration of the movement responses would be reflected in the accuracy and consistency of anticipation timing. A Bassin anticipation timer provided a light stimulus velocity of 3 mph for both experiments and the movements studied included a simple key press using a finger, an arm movement to a key press, and whole body movements culminating with a kick or step to a target. The experiments were modelled closely on the seminal study by Grose (1967). The results of Exp. 1 supported our prediction by demonstrating superiority of the finger task over the two larger movements for all measures of coincidence timing ability. The purpose of Exp. 2 was to compare the slightly different versions of the whole body task-that used in the first experiment and that used by Grose (1967). The results confirmed the close similarity of the two movement tasks and re-affirmed the results of Exp. 1. Exp. 2 also investigated sex effects on coincidence timing ability and, in contrast to previous evidence indicating that females perform with less accuracy and consistency than do males, no significant differences were found. Analysis of practice effects showed that, although there were no significant improvements over trial blocks in Exp. 1, there were significant improvements in Exp. 2. Comparisons with other research suggests that repeated practice in solving a coincident timing problem using whole body movements can lead to improved performance. In general, the findings are consistent with the constructs of action theory and emphasize the roles perceptual and movement variables have in defining situational constraints. Also, findings indicate that proficiency in coincidence anticipation appears to be influenced by the planning and organisation required for movement execution.

Adult↗
PubMed2001

Staining nucleic acids and proteins in electrophoresis gels.

This review addresses the most widely used stains for gel electrophoresis in molecular biology today. A brief introduction to electrophoresis is given, followed by a description of agarose and acrylamide gel formation. The major stains for nucleic acids are described, most of which are fluorescent and intercalate into the double helix structure of the nucleic acids. An ultraviolet transilluminator is necessary to visualize the fluorescent bands. The major protein stains include Coomassie blue, silver, and commercial fluorescent stains. Negative staining also can be used to stain the gel background, leaving the protein bands of interest transparent and visible against a white background.

Acrylic Resins↗
PubMed2000

Splicing before import - an intein in a mitochondrially targeted preprotein folds and is catalytically active in the cytoplasm in vivo.

Nuclear-encoded mitochondrial proteins are cytoplasmically synthesized and imported into the organelle. The intein-containing RecA protein of Mycobacterium tuberculosis, with or without the CoxIVp mitochondrial targeting signal (MTS), was used to determine where a protein targeted to mitochondria folds and becomes catalytically active. Analysis of fractions from Saccharomyces cerevisiae cells expressing RecA without the MTS revealed that RecA and intein proteins remained cytoplasmic. With the MTS, most of RecA was directed to mitochondria, while most of the intein remained in the cytoplasm. The intein therefore folds into a catalytically active state in the cytoplasm prior to RecA import into mitochondria.

Base Sequence↗
PubMed2000

Response timing and muscular coordination in fencing: a comparison of elite and novice fencers.

Reaction time (RT), movement time (MT), total response time (RMT) and accuracy of elite and novice fencers was studied under three levels of target choice (single-, two- and four-targets) with three variations of movement distance (short, medium and long lunge). In addition, electromyographic activity (EMG) of selected upper and lower limb muscles was used to compare the two groups. The elite subjects were faster for RT and RMT and displayed a higher level of accuracy. The hypothesis that increasing choice would cause increases in RT was not upheld. Except for some differentiation between the short and the two longer distances, the effects of movement distance were not marked. Qualitative and quantitative analysis of EMG revealed the high consistency of response patterns within subjects and highlighted the synergistic roles of selected muscles in distinguishing between elite and novice fencers. These findings confirm that differences in the technical skill of fencers can be distinguished in the laboratory through a combination of response timing measures in association with measures of muscle action. They also draw attention to practical implications for individual skill assessment and training. Analysis of pre-movement muscle activity provided moderate support for the hypothesis that it was part of a single control process and indicates that a dual process can involve both the maintenance of postural stability and the generation of movement. It is suggested that different movement contexts can lead to different levels of coordination between the system controlling posture and that controlling movement.

Adult↗
PubMed2000

Coping style following acute stress in competitive sport.

The purpose of this study was to ascertain coping styles among competitive athletes in response to various acute stressors. Specifically, the authors used a 134-item survey to measure approach and avoidance coping styles, with task-focused and emotion-focused coping tendencies nested hierarchically as subdimensions under each. Australian and U.S. college-aged participants indicated the extent to which they used approach, avoidance, task-focused, and emotion-focused coping strategies (a 4-factor model) in response to selected acute stressors experienced during sport competition. The authors computed confirmatory factor analysis to test the theoretically driven model. The criterion loading of .30 and above for each of the factors reduced the survey to 65 items. Findings indicated stronger links between the 2 approach constructs of task- and emotion-focused coping than between the 2 avoidance constructs of those subdimensions. The goodness-of-fit indices for the 4-factor model were 0.58 and 0.57 for Australian and U.S. samples, respectively, and .71 overall. Concomitant low correlations between the 2 approach (0.18) and the 2 avoidance dimensions (0.43) reflected relatively high residuals between stressors. In general, psychometric analyses suggest that coping style may be more prevalent in some situations than others, lending partial support for the transactional model of coping.

Acute Disease↗
PubMed2000

Sensitivity of testicular germ cells to toxicant-induced apoptosis in gld mice that express a nonfunctional form of Fas ligand.

Germ cell apoptosis in testis is essential for functional spermatogenesis. Recent evidence suggests that the Fas signaling system is critical for the regulation of testicular germ cell apoptosis. To further evaluate the Fas signaling system in testis, we examined the incidence of germ cell apoptosis in gld mice that lack a functional Fas-signaling pathway. gld mice have a small, but significant, increase in testis weight and numbers of spermatid heads per testis compared with wild-type mice. In addition, gld mice have a small increase in the spontaneous incidence of germ cell apoptosis, as indicated by characteristic DNA fragmentation via the terminal deoxynucleotidyl-transferase-mediated deoxy-UTP nick end labeling assay. To test the role of the Fas system in toxicant-induced germ cell apoptosis, mice were exposed to either a Sertoli cell- or germ cell-specific toxicant [mono-(2-ethylhexyl)phthalate (MEHP; 1 g/kg) or 5 Gy radiation, respectively]. These two exposure paradigms induced extensive increases in germ cell apoptosis in wild-type mice. However, exposure of gld mice to MEHP caused only a minimal increase in germ cell apoptosis, whereas they were as sensitive as wild-type mice to radiation exposure. These data indicate that the Fas signaling pathway is 1) involved in regulating the numbers of germ cells in the testis, 2) crucial for the initiation of germ cell apoptosis after MEHP-induced Sertoli cell injury, and 3) differentially active in the cell-specific regulation of germ cell apoptosis that occurs as a consequence of Sertoli cell vs. germ cell injury.

Animals↗
PubMed2000

Response amendment in fencing: differences between elite and novice subjects.

Reaction time (RT), movement time (MT), total response time (RMT), and accuracy of 3 elite and 3 novice fencers were studied under a dual response paradigm requiring a full lunge. Electromyographic activity (EMG) from selected arm and leg muscles was used to compare response profiles of the two groups. Although the elite subjects had slower MTs, their faster RTs resulted in significantly shorter total response times. The EMG analysis showed that in comparison to the novice subjects, onset of muscle activity was significantly faster for the elite group in five of the six muscles studied. In addition, the elite subjects showed more coherent muscle synergies and more consistent patterns of muscle coordination. Although the requirement to change targets (signalled by the arrival of a second stimulus) led to slightly more target misses for the elite group, the overall frequency was low, which indicates that it did not pose difficulty for either group. The present findings show that measures of response timing and neuromuscular coordination differentiate skill level in the fencing lunge and draw attention to practical implications for skill assessment and training.

Achievement↗
PubMed2000

Coincidence timing of a soccer pass: effects of stimulus velocity and movement distance.

The effect of stimulus velocity and movement extent on coincidence timing and spatial accuracy of a soccer pass was investigated. A Bassin anticipation timer provided light stimulus velocities of 1.79 or 2.68 m/sec. (designated as "Low" and "High", respectively), and subjects were required to kick a stationary soccer ball so that it struck a target in coincidence with the arrival of the light stimulus at the end of the runway. Two kick types were used. The "Short" condition began with the subject 70 cm from the ball and required a single forward step with the nonkicking leg before making the kick. The "Long" condition began 140 cm from the ball and required two steps before the kick. Twenty male subjects were given 16 trials under each of the four combinations of stimulus velocity and kick type. The expectation that the faster stimulus velocity would be associated with lower coincidence timing scores for both absolute error (AE) and variable error (VE) and with late responding for constant error (CEO) was upheld with the exception that for the Long Kick-High Velocity condition, AE was highest. The index of preprogramming (IP) was used to test the hypothesis that a two-stage control process would characterise coincidence anticipation performance involving whole-body movements. Results showed that the preparatory phase of responding produced zero-order IPs signifying reliance on feedback control. Also, while the striking phase produced high IP and suggested reliance on preprogrammed control, the possibility that the High Velocity conditions may have limited the responses was recognised. As a consequence, the role of open-loop processes remained equivocal. The findings are, however, in agreement with the view that the sensorimotor and movement-execution phases of responding require a process that is characterised by adaptability to regulatory features of the environment via closed loop mechanisms involving perception-action coupling.

Adult↗
PubMed1999

Novel, highly lipophilic antioxidants readily diffuse across the blood-brain barrier and access intracellular sites.

In an accompanying article, an in vitro assay for permeability predicts that membrane-protective, antioxidant 2,4-diamino-pyrrolo[2, 3-d]pyrimidines should have improved blood-brain barrier (BBB) permeation over previously described lipophilic antioxidants. Using a first-pass extraction method and brain/plasma quantification, we show here that two of the pyrrolopyrimidines, one of which is markedly less permeable, readily partition into rat brain. The efficiency of extraction was dependent on serum protein binding, and in situ efflux confirms the in vitro data showing that PNU-87663 is retained in brain longer than PNU-89843. By exploiting inherent fluorescence properties of PNU-87663, its distribution within brain and within cells in culture was demonstrated using confocal scanning laser microscopy. PNU-87663 rapidly partitioned into the cell membrane and equilibrates with cytoplasmic compartments via passive diffusion. Although partitioning of PNU-87663 favors intracytoplasmic lipid storage droplets, the compound was readily exchangeable as shown by efflux of compound from cells to buffer when protein was present. The results demonstrated that pyrrolopyrimidines were well suited for quickly accessing target cells within the central nervous system as well as in other target tissues.

Animals↗
PubMed1998

Clonal production of tea tree oil high in terpinen-4-ol for use in formulations for the treatment of thrush.

A programme of evaluation and selection of superior trees has led to the vegetative propagation of highly productive clones which produce tea tree oil high in terpinen-4-ol. These will soon provide commercial quantities of a particularly active oil of consistent quality for use in formulations for therapeutic use and in particular for vaginal thrush.

Anti-Infective Agents, Local↗
PubMed1997

Glial cell line-derived neurotrophic factor protects against ischemia-induced injury in the cerebral cortex.

Glial cell line-derived neurotrophic factor (GDNF), a recently described and cloned member of the transforming growth factor (TGF)-beta superfamily, has been shown to have marked trophic activity on several populations of central neurons. Survival-promoting and injury protectant activity in vitro and in vivo, using several paradigms, has been demonstrated for ventral mesencephalic dopaminergic neurons and spinal cord motoneurons. In view of a proposed commonality of mechanisms, involving intracellular free radical generation, depolarization-induced Ca2+ influx, and mitochondrial respiratory enzyme injury, between such GDNF-responsive paradigms and those of ischemia-induced injury, we tested the effects of GDNF on the extent of neural degeneration induced by transient middle cerebral artery (MCA) occlusion. We now report that intracerebroventricular and intraparenchymal administration of GDNF potently protects the cerebral hemispheres from damage induced by MCA occlusion. In addition, the increase in nitric oxide that accompanies MCA occlusion and subsequent reperfusion is blocked almost completely by GDNF. Thus, this protein may play an important role in the treatment of cerebrovascular occlusive disease.

Age Factors↗
PubMed1997

Stochastic completion fields; a neural model of illusory contour shape and salience.

We describe an algorithm- and representation-level theory of illusory contour shape and salience. Unlike previous theories, our model is derived from a single assumption: that the prior probability distribution of boundary completion shape can be modeled by a random walk in a lattice whose points are positions and orientations in the image plane (i.e., the space that one can reasonably assume is represented by neurons of the mammalian visual cortex). Our model does not employ numerical relaxation or other explicit minimization, but instead relies on the fact that the probability that a particle following a random walk will pass through a given position and orientation on a path joining two boundary fragments can be computed directly as the product of two vector-field convolutions. We show that for the random walk we define, the maximum likelihood paths are curves of least energy, that is, on average, random walks follow paths commonly assumed to model the shape of illusory contours. A computer model is demonstrated on numerous illusory contour stimuli from the literature.

Algorithms↗
PubMed1997

Regional distribution of iron, transferrin, ferritin, and oxidatively-modified proteins in young and aged Fischer 344 rat brains.

Iron dysregulation in the brain is thought to contribute to the oxidative damage seen in neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. A role for iron in the oxidative stress thought to contribute to normal ageing is less certain. To better characterize the role of iron in normal ageing, the concentrations of iron, transferrin, ferritin, and protein carbonyl groups are measured in nine separate regions of Fischer 344 rats. The largest (approximately 30%) age-related increases in brain iron concentration are seen in the temporal cortex, medial septum, and cerebellum. Ferritin concentration in these same brain regions increases 50 to 250% with age, while protein carbonyl concentration is only -27 to +4%, of young rats. These results indicate that an increase in the major iron-binding protein ferritin compensates for any age-related increase in iron concentration, and suggest that the increased ferritin is cytoprotective, serving to prevent the accumulation of protein carbonyl groups (a principal product of metal-catalysed oxidation of proteins).

Aging↗
PubMed1997

Identification of superoxide dismutase activity in Borrelia burgdorferi.

Infective and noninfective strains of Borrelia burgdorferi, along with Borrelia afzelii and Borrelia garinii, possessed a single iron-containing superoxide dismutase (SOD). None of the Lyme disease spirochetes tested possessed catalase or peroxidase activities. The borrelial SOD was not inducible by growth with increased oxygen concentrations and thus appeared to be produced constitutively.

Borrelia burgdorferi Group↗
PubMed1996

Brain-derived neurotrophic factor, but not neurotrophin-3, prevents ischaemia-induced neuronal cell death in organotypic rat hippocampal slice cultures.

We have investigated the neuroprotective actions of neurotrophins in a model of ischaemia using slice cultures. Ischaemia was induced in organotypic hippocampal cultures by simultaneous oxygen and glucose deprivation. Cell death was assessed 24 h later by propidium iodide fluorescence. Pre- but not post-ischaemic addition of brain-derived neurotrophic factor (BDNF) produced a concentration-dependent reduction in neuronal damage. Neurotrophin-3 was not neuroprotective. These data suggest that BDNF may form part of an endogenous neuroprotective mechanism.

Animals↗
PubMed1996

Evidence for DNA fragmentation in the CNS of aged Fischer-344 rats.

The aged central nervous system (CNS) is characterized by a loss of neurons. Apoptosis has been reported to be responsible for neuronal death during development and may also be involved in some age-related neurodegenerative diseases of the CNS. No evidence is currently available as to whether apoptosis is also responsible for the loss of neurons associated with physiological aging. In this study, we have found fragmented DNA, a characteristic trait of cells undergoing apoptosis, in the hippocampus and, to a minor extent, in the frontal cortex and basal forebrain of aged (24-month-old) Fisher-344 rats, but not in the cerebellum. These data represent important evidence to support the idea that apoptosis may be associated with the neuronal death observed during normal aging.

Aging↗