Search PubMed⌕ Search

Biomedical subjects

M A Wilson

Publications and source records attributed to M A Wilson.

At least 217 records · Page 12Linked to original sources
PubMed1991

Interaction of monovalent ions with the water liquid-vapor interface: a molecular dynamics study.

Results of molecular dynamics studies on the ions Na+, F-, and Cl- near the water liquid-vapor interface are reported. The free energies required to move the ions to the interface are presented and shown to depend on the sign of the ionic charge, and not the size of the ion. F- and Cl- can approach to within 2 molecular layers of the interface without incurring a significant change in free energy, while it costs about 2.5 kcal/mole to move Na+ this same distance. The free energy differences between the cation and the anions arise from the interaction of the ions with the water molecules in the interfacial region. These water molecules are oriented with a slight preference for their molecular dipoles to point toward the liquid. Thus, the anions approaching the interface disrupt the water structure less than does the cation. The calculated free energy curves are compared with predictions of simple dielectric models. It is shown that these models do not provide a good description of ions at the water surface. The ions are found to retain their first solvation shells at the interface. The anions also retain part of their second solvation shells, while Na+ does not. As a result, a larger bulge in the water surface is observed above the anions than above Na+. The lateral mobilities of the ions increase at the interface, in qualitative agreement with predictions of hydrodynamic models.

Chemical Phenomena↗
PubMed1991

Current status and rationale for composite inlays and onlays.

Composite inlay systems, now available to the dental profession, are classified and evaluated. Principle motives for their deployment are the aviodance or reduction of in situ polymerisation shrinkage and the optimisation of restoration contour and adaptation. The criteria for placement of direct or indirect composite inlay restorations are critically reviewed in relation to alternative materials and operative procedures. Dimensions of typical molar and premolar inlay cavities are presented and interim guidelines for inlay cavity design are discussed.

Composite Resins↗
PubMed1991

Discordance between accumulation of C-14 deoxyglucose and Tl-201 in reperfused myocardium.

Radiolabeled deoxyglucose (FDG) has been advocated as a marker of viability of reperfused myocardium during acute infarction. However, data for such recommendation are few. We investigated cardiac deposition of C-14 deoxyglucose (C-14 DG) and of Thallium -201 (Tl-201) in rabbits subjected to coronary occlusion (15, 30, 60 or greater than 100 min) and reperfusion (75 min and 24 h). Measured myocardial concentrations of C-14 DG and Tl-201 in macroautoradiograms were quantitatively correlated in a 24 h reperfusion group with presence of myocardial necrosis evaluated by light microscopy. The major finding in this investigation was that with 30 min or 60 min of ischemia followed by reperfusion there were myocardial regions with significant hypoperfusion (Tl-201) and histologic necrosis. However, in the same myocardial areas, the deposition of C-14 DG was not correlated with the extent of necrosis (r = 0.27). Also, the deposition of C-14 DG in acute myocardial infarction was higher than that of Tl-201 (P = 0.05 by paired T test and by nonparametric Wilcoxon's test). It was also demonstrated that when the occlusion time was varied (15-130 min) and early reperfusion was provided for 75 min or omitted altogether, the myocardial accumulation of Tl-201 was variable and that myocardial sequestration of C-14 DG was higher than perfusion in central and peripheral portions of the area-at-risk. These observations do not support a role for the use of radiolabeled deoxyglucose for the detection of myocardial viability in recently infarcted cardiac muscle.

Animal Nutritional Physiological Phenomena↗
PubMed1991

Performance of occlusin in butt-joint and bevel-edged preparations: five-year results. 4.

The five-year findings of a study to compare the performance of restorations of Occlusin (ICI Dental, Macclesfield, UK) in butt-joint and bevel-edged preparations are reported. Ninety-four (79%) of the restorations originally placed were reviewed at five years, 20 restorations (17%) having failed during the study. Initial analysis of the overall results having failed to reveal any significant differences between the five-year performance of the two types of restorations, the results were combined and analyzed by Chi-square tests and step-wise logistic regression. Chi-square analysis indicated that of the independent variables investigated, size of restoration had the greatest effect on clinical performance. Step-wise logistic regression revealed that only four of the eight dependent variables investigated showed significant predictive relationships with the independent variables, the logistic equation for occlusal marginal adaptation being the most complex. The greatest amount of generalized occlusal surface wear tended to be seen in large-sized Class II restorations in molar teeth, with the main factor influencing wear being found to be the type of restoration (Class I or Class II). It is concluded that the performance of restorations of Occlusin has not been found to differ significantly in butt-joint and bevel-edged preparations after five years in clinical service. Step-wise logistic regression has been found to be a useful tool in the analysis of data obtained during the clinical evaluation of a restorative material.

Adolescent↗
PubMed1991

The organization of serotonergic projections to cerebral cortex in primates: regional distribution of axon terminals.

Serotonergic axons are widely distributed in the primate forebrain and represent the most abundant ascending projection from the reticular formation. Immunocytochemical methods have been utilized to examine the density, laminar distribution and morphology of serotonergic axons in both primary projection (motor, somatosensory) and association areas (dorsolateral prefrontal, area 5) as well as in the hippocampus and in cingulate cortex of rhesus and cynomolgus macaques. Serotonergic axons are present in all areas of cortex examined, and all cortical layers receive serotonergic afferents. However, the intracortical distribution of serotonergic axon terminals is not uniform; rather, different regions of cortex exhibit dissimilarities in both the density and laminar distribution of serotonergic axons. Thus, there are local patterns of serotonin innervation that are characteristic of each cortical area. Highly diverse patterns of serotonin innervation are found in heterotypical areas of cortex; more subtle variations are present among homotypical areas. Two morphologic types of serotonergic axon terminals, fine and beaded, are present in all cortical areas, and they typically exhibit different laminar distributions: in most areas of neocortex, beaded axons predominate in layer I while fine axons predominate in layers II-VI. However, exceptions to this pattern were observed in primary visual cortex and in the hippocampal formation. The distinctive local patterns of serotonin innervation observed in this study indicate that raphe-cortical projections are likely to have differential influences on particular cytoarchitectonic areas of cerebral cortex in the primate. Moreover, the discrete laminar distribution of serotonin axons suggests that serotonergic projections selectively innervate particular neuronal elements in cerebral cortex. The present findings suggest that the two classes of serotonergic axons, fine and beaded, which have different patterns of termination, affect different sets of cortical neurons. In addition, these two serotonergic projections may be associated with different sets of serotonergic receptors and thus produce selective effects on cortical function.

Afferent Pathways↗
PubMed1991

The organization of serotonergic projections to cerebral cortex in primates: retrograde transport studies.

Retrograde axonal transport and immunocytochemical methods were utilized to determine the origin of serotonergic afferents to selected primary projection and association areas of cerebral cortex in macaque monkeys. After injections of Fast Blue or Diamidino Yellow in primary motor, somatosensory, or visual cortex, retrogradely labeled neurons are found in both the dorsal and median raphe nuclei. The sets of dorsal raphe neurons which innervate these cortical areas differ in their spatial distributions along the rostrocaudal axis of the brainstem; a coarse rostrocaudal topographic relationship is found between these groups of dorsal raphe neurons and their cortical targets. In contrast, neurons in the median raphe which innervate these primary projection areas are not differentially distributed along the rostrocaudal axis. However, in both the median and dorsal raphe nuclei, most neurons projecting to primary visual cortex are situated lateral to the cells which project to motor and somatosensory areas; many of these visually projecting neurons lie among the fascicles of the medial longitudinal fasciculus. For comparison with the serotonergic innervation of primary projection areas, the locations of raphe cells projecting to three areas of association cortex were examined: dorsolateral prefrontal cortex, area 5 and area 7b. Neurons projecting to each of these association areas are found throughout the dorsal and median raphe nuclei. Their distributions are similar to one another; however, more cells projecting to dorsolateral prefrontal cortex are in the rostral part of the dorsal raphe. The dorsal and median raphe neurons projecting to these association areas are intermingled with neurons projecting to motor and somatosensory cortex, but are medial to most of those projecting to visual cortex. Thus, separate cortical areas are innervated by different sets of raphe neurons; these sets partially overlap, yet differ in their rostrocaudal and mediolateral distributions. Ascending serotonergic projections to cerebral cortex form a widely distributed system which exhibits a highly intricate anatomic organization. The present observations support the hypothesis that the dorsal raphe nucleus is comprised of distinct sets of neurons whose output is distributed to multiple, interconnected cortical areas; these serotonergic projections may play a role in the coordination of excitability in functionally related areas of cortex. In contrast, the serotonergic projections arising from the median raphe appear to be more divergent and are likely to have a global influence on cortical activity. Since these individual raphe nuclei have different projection patterns, they are likely to have distinct functional roles.

Afferent Pathways↗
PubMed1991

Early events in initiation of alternative complement pathway activation by the capsule of Cryptococcus neoformans.

The capsule of Cryptococcus neoformans is a powerful activator of the alternative complement pathway. This study examined the manner in which the cryptococcal capsule influences initiation of and early events in complement activation by C. neoformans. These studies examined the effects of the classical and alternative pathways on the kinetics and early sites for deposition of C3 fragments on encapsulated cryptococci, nonencapsulated cryptococci, and zymosan. The results showed that nonencapsulated cryptococci and zymosan are qualitatively and quantitatively similar in the manner in which they initiate complement activation. Both utilize the classical and alternative pathways. Initiation via the classical pathway occurs suddenly and simultaneously at sites distributed over the entire cell surface. Initiation of the alternative pathway by zymosan and nonencapsulated cryptococci is characterized by a lag of 6 to 8 min before appreciable amounts of C3 accumulate on the cells. Alternative pathway initiation by zymosan and nonencapsulated cryptococci occurs at a limited number of focal initiation sites that expand with alternative pathway amplification to cover the cell surface. Presence of the cryptococcal capsule blocks classical pathway initiation, which would normally occur at the cryptococcal cell wall, and produces an initiation that is dependent solely on the alternative pathway. Initiation of the alternative pathway by the cryptococcal capsule is characterized by a lag in C3 accumulation and the appearance of a limited number of focal initiation sites which resemble those observed when the alternative pathway is activated by zymosan and nonencapsulated cryptococci.

Complement Activation↗
PubMed1991

Survey to estimate prevalence of Leptospira interrogans infection in mature cattle in the United States.

A total of 5,142 kidney tissue samples and 5,111 serum samples from mature cattle in 49 states and Puerto Rico were collected at slaughter. Age of cattle ranged from 1 to 16 years (mean, 6.6 years). Leptospires were isolated from 88 (1.7%) kidney tissues, and 2,493 (49%) sera contained antibodies against 1 or more of 12 Leptospira interrogans serovars. Leptospires were observed by immunofluorescence in 41 (0.8%) kidney tissues. Using agglutinin-absorption tests, 73 (83%) isolates were identified as serovar hardjo, 11 (12.5%) as serovar pomona, and 4 (4.5%) as serovar grippotyphosa. By use of restriction endonuclease analysis studies of chromosomal DNA, all isolates differed from reference serovars but were identical to strains previously isolated from cattle or swine in the United States. Of the serovar hardjo isolates, 85% were identical to restriction endonuclease analysis type (genotype) hardjo-bovis A and 11 (15%) were identical to genotype hardjo-bovis B. Serovar pomona isolates were identical to genotypes kennewicki A (64%) or kennewicki B (36%), and serovar grippotyphosa isolates were identical to the RM 52 strain. Isolation rates were significantly (P less than 0.001) higher for beef cattle than for dairy cattle and were higher (P less than 0.001) for bulls than for cows. Combined culture and immunofluorescence results indicated that 2% of mature cattle were renal carriers of leptospires.

Agglutination Tests↗
PubMed1991

Relationships between prevalence of Leptospira interrogans in cattle, and regional, climatic, and seasonal factors.

On the basis of serologic test results and isolation of leptospires from mature cattle, distribution and prevalence of Leptospira interrogans serovars and genotypes were compared by state and region of the United States. Relationships between isolation rate and month of sample collection, mean regional temperature, and mean regional precipitation were examined. Isolation rate and seroprevalence were significantly (P less than 0.001) higher for southeastern, south central, and Pacific coastal regions than for other regions of the United States. Isolates of genotypes hardjo-bovis A and kennewicki A and B, and of serovar grippotyphosa appeared to be randomly distributed. Genotype hardjo-bovis B isolates came from a southern area of the country that extends from Georgia to New Mexico. To the authors' knowledge, this is the first recorded isolation of serovar hardjo from Hawaii. Although significant relationship was not documented between isolation rate and month or season of the year, seroprevalence for summer, fall, and winter was significantly (P less than 0.001) higher than that for spring. Regional isolation rate was related more to mean temperature (r = 0.83; P less than 0.05) than to mean precipitation amount (r = 0.34; P greater than 0.50).

Animals↗
PubMed1990

Regeneration of optic fibres through the chiasma in Xenopus laevis tadpoles.

The path through the chiasma followed by regenerating optic nerve fibres in Xenopus tadpoles was studied at light- and electron-microscopic levels, and with horseradish peroxidase as a fibre label. Over the period (5-10 days) in which regenerating fibres reach and cross the chiasma, they did not follow residual deep fibres through the chiasma, nor were they associated with the trail of degeneration in the chiasma which represented the remains of the deeper (older) parts of the original projection. The regenerating optic fibres were always seen in close association with the inner surfaces of the ependymoglial endfeet, or in the extracellular spaces that lie close to the endfeet in the most superficial part of the chiasma, where newly-growing fibres from the retinal margin are normally to be found.

Animals↗
PubMed1990

A topographic study of differences in the P300 between introverts and extraverts.

This paper presents results of a study to establish a link between neurocognitive psychophysiological and psychological type data through the investigation of differences in topographic auditory event-related potential (AERP) (P300) patterns in strongly introverted (n = 17) and strongly extraverted ( = 16) high school males as identified by the Myers Briggs Type Indicator. Group data files were created for the auditory event related potential task and converted to ASCII form. Amplitude values were evaluated at each scalp site. Kruskal Wallis one way analysis of variance was performed to evaluate group differences. In processing of infrequent, target stimuli, the amplitude of the P300 waveform for introverts was higher than for extraverts. When processing for non-target stimuli was subtracted from target stimuli, statistical differences were found over nine central, parietal, and occipital sites. The findings support and extend theories of biologically-based and bio-psycho-social typology.

Acoustic Stimulation↗
PubMed1990

Glycolysis in Anolis carolinensis during agonistic encounters.

We examined the influences of territorial status, encounter outcome, body mass difference, activity, and display on lactate accumulation in adult male Anolis carolinensis during agonistic interactions. Of the pairs of lizards frozen at the onset of an encounter, intruders had significantly higher lactate concentrations than residents. Lactate levels at the onset of an interaction were not significantly different from those at the conclusion, suggesting a limited role for glycolysis during such events. The outcome of an agonistic encounter was not based on fatigue. Individuals that were larger or changed sites had a lower relative lactate concentration at the conclusion of an interaction than smaller or sedentary animals. We consider the influence of autonomic arousal on glycolysis.

Agonistic Behavior↗
PubMed1990

Chloroplast DNA evolves slowly in the palm family (Arecaceae).

A survey of cpDNA restriction-site variation for 22 species representing five of the six subfamilies of the palm family was conducted. Phylogenetic reconstructions based on the restriction-site data are in general agreement with conventional analyses based on morphological characters. Base-substitution estimates, derived from the restriction-site data, indicate a potential 5-13-fold decrease in substitution rates within the palms relative to rate estimates for annual plant taxa. Approximately 1,000 bp of the rbcL gene (ribulose-1,5-bisphosphate carboxylase, large subunit) were sequenced from species representing two subfamilies of the palms. The complete DNA sequence data are in accord with the restriction-site data and indicate a total rate of nucleotide substitution that is about eightfold lower than that observed for annual plants.

Base Sequence↗
PubMed1990

Treatment of obesity.

Decreases in resting metabolic rate and thermic effect of exercise during and after caloric restriction contribute to a reduced rate of weight reduction and subsequent difficulty in weight maintenance. Increasing exercise increases the thermic effect of exercise and prevents a decrease in resting metabolic rate, thereby, improving the rate of weight loss. A combined program of caloric restriction, exercise, and behavior therapy (including relapse prevention training and social support systems) is the most successful approach to long term weight reduction efforts. Pharmacologic treatment is currently limited, but there are three areas of development: agents which reduce energy intake, inhibitors of lipid synthesis, and thermogenesis enhancers. Evidence for improving efficiency of weight loss prevention and prevention of weight regain during repeated cycles of dieting (yo-yo phenomenon) exists in rat studies but not in a preliminary human investigation.

Basal Metabolism↗
PubMed1990

Current methods of treating and preventing myopia.

In this review, we discuss and compare current methods of treating and preventing myopia including radial keratotomy, keratomileusis, keratophakia, epikeratoplasty, keratokyphosis, scleral reinforcement, phakoemulsification, and heat application. Among the visual training methods are such procedures as biofeedback and behavior modification. The use of drugs, orthokeratology, spectacles, bifocals, prisms, intraocular lenses, contact lenses, and ultrasound are described.

Humans↗