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Biomedical subjects

M A Wilson

Publications and source records attributed to M A Wilson.

At least 181 records · Page 10Linked to original sources
PubMed1994

Integrin-mediated collagen gel contraction by cardiac fibroblasts. Effects of angiotensin II.

Angiotensin II (Ang II), a vasoactive octapeptide, has been implicated in cardiac growth and the development of hypertrophy and fibrosis secondary in hypertensive disease. These consequences of Ang II imply an effect on the function and morphology of cardiac interstitial cells (fibroblasts). The present investigation was designed to (1) determine whether neonatal heart fibroblasts (NHFs) possess functional Ang II receptors on their plasma membrane and (2) examine the effects of Ang II on NHFs in vitro using three- and two-dimensional (3D and 2D, respectively) cultures. Several analytic techniques were used to test the specific questions of the present study. Since cardiac fibroblast phenotype can be influenced by culture conditions, both 2D and 3D cultures were used in the present investigations. Reverse-transcriptase polymerase chain reaction and radioligand binding analysis were used to test for the presence of Ang II receptors on NHFs. Both revealed that NHFs in 2D culture possess Ang II receptor mRNA and Ang II receptors. When isolated NHFs were cultured in 3D collagen gels and treated with Ang II, gel contraction was stimulated by NHFs. This effect was attenuated by the specific Ang II receptor antagonist [Sar1,Ala8]Ang II. Ang II-stimulated gel contraction was completely inhibited by extracellular matrix receptor (beta 1-integrin) antibodies (P < .05), supporting previous studies indicating that collagen gel contraction is mediated via the integrins. Immunofluorescent staining was used to test the localization of cell-surface integrins. A more intense staining pattern for beta 1-integrin in Ang II-treated versus control cells was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Nitric oxide synthase inhibition exacerbates sepsis-induced renal hypoperfusion.

BACKGROUND: Hyperdynamic sepsis is often complicated by renal dysfunction, caused in part by renal vasoconstriction and impaired blood flow. Nitric oxide (NO) is an important mediator of hemodynamic responses to sepsis; however, its importance in the renal microcirculation during sepsis is unknown. Our purpose was to determine the role of NO in the renal microcirculation during bacteremia. METHODS: In vivo videomicroscopy was used to study the microcirculation in five groups of hydronephrotic rat kidneys. Cardiac output (CO), mean arterial pressure, interlobular artery (ILA) diameter and flow, and afferent (AFF) and efferent arteriole diameters were measured. RESULTS: NO synthase inhibition in normal rats resulted in hypertension, decreased CO, selective preglomerular constriction (ILA, -21%; AFF, -26% of baseline), and hypoperfusion (-56%). Escherichia coli resulted in a normotensive, high CO state (+23%) with ILA (-25%) and AFF (-20%) constriction and hypoperfusion (-60%). NO synthase inhibition during bacteremia normalized CO and increased mean arterial pressure (+34%) but exacerbated constriction (ILA, -45%; AFF, -33%) and further impaired flow (-90%). CONCLUSIONS: NO maintains preglomerular tone and flow during basal conditions and appears to counteract intrarenal vasoconstrictors during E. coli bacteremia.

Amino Acid Oxidoreductases↗
PubMed1994

Intravenous and central catheter infections.

Catheter-associated infections are quite common in hospitalized patients and account for significant morbidity and mortality. Multiple causative factors are present in everyday clinical practice to account for these infections. A high index of suspicion for these infections is needed in any evaluation of a patient who has a febrile illness. Removal of the catheter and quantitative culture are necessary initial steps in treatment, and systemic antibiotic therapy, based on specific culture results, is indicated in any patient whose systemic signs of infection do not resolve promptly. In the absence of such a response, other sources of infection should be sought; however, one must maintain a high index of suspicion for the local site of catheter insertion, and repeated examination of all insertion sites is indicated until the fever resolves.

Bacterial Infections↗
PubMed1993

Dynamics of the hippocampal ensemble code for space.

Ensemble recordings of 73 to 148 rat hippocampal neurons were used to predict accurately the animals' movement through their environment, which confirms that the hippocampus transmits an ensemble code for location. In a novel space, the ensemble code was initially less robust but improved rapidly with exploration. During this period, the activity of many inhibitory cells was suppressed, which suggests that new spatial information creates conditions in the hippocampal circuitry that are conducive to the synaptic modification presumed to be involved in learning. Development of a new population code for a novel environment did not substantially alter the code for a familiar one, which suggests that the interference between the two spatial representations was very small. The parallel recording methods outlined here make possible the study of the dynamics of neuronal interactions during unique behavioral events.

Animals↗
PubMed1993

In vivo effects of endothelin on the renal microcirculation.

Endothelin-1 (ET) is a recently discovered vasoconstrictor peptide which is released by renal vascular endothelial cells in response to a number of pathologic insults including ischemia, endotoxemia, bacteremia, and cyclosporine nephrotoxicity. Because microvascular vasoconstriction is an integral component of the acute renal dysfunction associated with these conditions, this study was undertaken to determine the in vivo effects of ET on the renal microcirculation. We used the split hydronephrotic kidney model in decerebrate Sprague-Dawley rats to study vessel diameter and red cell velocity responses to ET using intravital videomicroscopy and doppler velocimetry. Topical administration of increasing concentrations of ET caused a dose-dependent constriction of interlobular arteries which reached a maximum of 27 +/- 5% at an ET concentration of 10(-8) M. A corresponding decrease of 64 +/- 8% in interlobular arterial blood flow was observed. Afferent and efferent arteriole diameters were reduced by 39 +/- 2% and 27 +/- 5%, respectively. These vascular effects were completely prevented by the systemic preinfusion of anti-endothelin antiserum. Infusion of antiserum alone had no effect on systemic hemodynamics or renal microvascular variables, suggesting that ET has little or no role in maintaining basal vascular tone in the kidney. We conclude that ET is a potent in vivo constrictor of the renal microcirculation and may be involved in mediating pathologic vasoconstriction.

Animals↗
PubMed1993

Endothelins mediate intestinal hypoperfusion during bacteremia.

We have previously reported that Escherichia coli bacteremia induces hypoperfusion and vasoconstriction of the rat small intestinal microcirculation. However, the mechanisms which mediate these responses are not clearly defined. Because serum levels of endothelins, a family of potent vasoconstrictor peptides, are increased during bacteremia, we postulated that endothelins contribute to intestinal hypoperfusion during infection. Using intravital microscopy, we characterized the effects of topically applied recombinant endothelin-1 on small intestinal arteriolar diameters and blood flow. Dose-dependent vasoconstriction of both large (A1) and small (A3) arterioles and hypoperfusion were observed. To assess whether endothelins contribute to alterations of the intestinal microcirculation during bacteremia, antiserum was used to inhibit endothelins during E. coli bacteremia. Endothelin inhibition resulted in restoration of blood flow and attenuation of vasoconstriction. Our results suggest that endothelins contribute to intestinal hypoperfusion and arteriolar vasoconstriction during bacteremia.

Animals↗
PubMed1993

Optic synapses are found in diencephalic neuropils before development of the tectum in Xenopus.

The position of the earliest optic synapses in Xenopus and the stage at which they developed were studied with the electron microscope after labelling of optic axons with horseradish peroxidase. In addition, tritiated thymidine autoradiography and bromodeoxyuridine immunohistology were used to identify the birth dates of cells in the regions where the synapses had been found. The earliest mature optic synapses were found in the mid-diencephalic region, where the major diencephalic optic neuropils were beginning to develop. These synapses were seen at stage 35/36, before cells in the tectal precursor region had become postmitotic. In other animals labelling with tritiated thymidine or bromodeoxyuridine showed that cells in the diencephalon, close to where the synapses had been seen, were becoming postmitotic at the time the earliest optic axons arrived. The first optic synapses to form in the developing Xenopus visual system thus appeared to do so in the neuropil of Bellonci and the rostral visual nucleus.

Animals↗
PubMed1993

Gonadectomy and sex modulate spontaneous activity of substantia nigra pars reticulata neurons without modifying GABA/benzodiazepine responsiveness.

Gonadal steroid hormones or their derivatives can alter the GABA receptor complex and GABA-mediated responses. This study examines the influences of the in vivo gonadal steroid milieu on neuronal responses to GABA and benzodiazepine agonists in the substantia nigra pars reticulata (SNr) of rats. Spontaneous activity and microiontophoretic sensitivity to GABA of single SNr neurons were analyzed in chloral hydrate anesthetized intact male, intact female, orchidectomized male, and ovariectomized female rats using extracellular electrophysiological techniques. Benzodiazepine responses in each hormone group were assessed as 1) the ability of the iontophoretically applied midazolam to enhance GABA sensitivity and 2) the ability of systemically administered diazepam to decrease SNr firing rate. The results indicate that neither sex nor castration modified GABA sensitivity or benzodiazepine responsiveness in the SNr. However, a heightened level of basal SNr activity was observed in males compared to orchidectomized, intact female, or ovariectomized rats. Elevated SNr activity was also observed in males compared with other hormone groups following iontophoretic application of the GABA antagonist SR95531, suggesting that this augmentation in firing rate may be independent of nigral GABAergic control. Regulation of in vivo spontaneous SNr activity may be associated with gonad-related influences on the nigrostriatal system, but appears unrelated to intrinsic alterations in GABA/benzodiazepine responses in this area.

Action Potentials↗
PubMed1993

Viewpoint 9--molecular structure of aqueous interfaces.

In this review we summarize recent progress in our understanding of the structure of aqueous interfaces emerging from molecular level computer simulations. It is emphasized that the presence of the interface induces specific structural effects which, in turn, influence a wide variety of phenomena occurring near the phase boundaries. At the liquid-vapor interface, the most probable orientations of a water molecule is such that its dipole moment lies parallel to the interface, one O-H bond points toward the vapor and the other O-H bond is directed toward the liquid. The orientational distributions are broad and slightly asymmetric, resulting in an excess dipole moment pointing toward the liquid. These structural preferences persist at interfaces between water and nonpolar liquids, indicating that the interactions between the two liquids in contact are weak. It was found that liquid-liquid interfaces are locally sharp but broadened by capillary waves. One consequence of anisotropic orientations of interfacial water molecules is asymmetric interactions, with respect to the sign of the charge, of ions with the water surface. It was found that even very close to the surface ions retain their hydration shells. New features of aqueous interfaces have been revealed in studies of water-membrane and water-monolayer systems. In particular, water molecules are strongly oriented by the polar head groups of the amphiphilic phase, and they penetrate the hydrophilic head-group region, but not the hydrophobic core. At infinite dilution near interfaces, amphiphilic molecules exhibit behavior different from that in the gas phase or in bulk water. This result sheds new light on the nature of hydrophobic effect in the interfacial regions. The presence of interfaces was also shown to affect both equilibrium and dynamic components of rates of chemical reactions. Applications of continuum models to interfacial problems have been, so far, unsuccessful. This, again, underscores the importance of molecular-level information about interfaces.

Computer Simulation↗
PubMed1993

In vitro comparison of conventional crowns and a new all-ceramic system.

Thirty-three crowns of similar size and shape were constructed to fit a standard brass die. Eleven crowns were manufactured from each of the following groups of materials: metal-ceramic, aluminous porcelain and a new all-ceramic system based on a glass infiltrated alumina coping. The overall fitting accuracy of each crown was determined using a low viscosity silicone paste, prior to cementation onto brass dies with zinc phosphate cement. The average film thickness was 95, 154 and 123 microns respectively. Each cemented crown was loaded to fracture. The mean load to failure of the glass infiltrated alumina crowns was significantly greater than that of the aluminous porcelain jacket crowns (P < 0.0001), but not significantly different from the metal-ceramic crowns.

Aluminum Oxide↗
PubMed1993

Accelerated decay of C3b to iC3b when C3b is bound to the Cryptococcus neoformans capsule.

Incubation of encapsulated and nonencapsulated Cryptococcus neoformans in normal human serum (NHS) leads to activation and binding of potentially opsonic fragments of complement component C3 to the yeast cells. Analysis of the molecular forms of C3 after incubation of encapsulated cryptococci in NHS showed that the percentage of bound C3 occurring as iC3b approached 100% after 8 min. The percentage of bound C3 occurring as iC3b on nonencapsulated cryptococci never exceeded 70%, even after 60 min of incubation in NHS. Conversion of C3b to iC3b was assessed further by incubating C3b-coated cryptococci for various times with a mixture of complement factors H and I at 40% of their respective physiological concentrations. Most, if not all, of the C3b on encapsulated cryptococci was converted to iC3b at a single fast rate. Conversion of C3b to iC3b on nonencapsulated cryptococci did not follow a single rate constant and appeared to have a fast and a slow component. Studies of the requirements for factors H and I in cleavage of C3b to iC3b showed steep dose-response curves for both factors in the case of encapsulated cryptococci and shallow curves with C3b bound to nonencapsulated cryptococci. Taken together, our results indicate that C3b molecules bound to encapsulated cryptococci have a uniformly high susceptibility to conversion to iC3b by factors H and I. In contrast, a significant portion of the C3b bound to nonencapsulated cryptococci is very resistant to conversion to iC3b by factors H and I.

Complement C3b↗
PubMed1993

Comparison of DNA fingerprinting and serotyping for identification of avian Pasteurella multocida isolates.

The DNA fingerprint profiles and serotypes of 63 avian Pasteurella multocida field isolates, 13 attenuated vaccine isolates (propagated from vaccines manufactured by five companies), and 16 somatic reference strains were compared. DNA fingerprinting established the relationship of isolates that could not be distinguished by serotyping. Of the 76 isolates, 28 DNA fingerprint profiles and 12 somatic types were recognized. One isolate was nonreactive with 16 reference somatic and 5 reference capsule-type antisera. Thirty-one field isolates and seven vaccine isolates were identified as capsule type A. Twenty-nine field isolates and six vaccine isolates were nonencapsulated. Three field isolates were capsule type F. Isolates of capsule types B, D, and E were not found. One field isolate, identified as somatic type 7, had a DNA fingerprint identical to that of the somatic reference type 6 profile. Twelve field isolates had profiles identical to the somatic reference type 3 strain profile; 11 of these were identified as somatic type 3, 4, and 1 was identified as somatic type 3. The DNA fingerprint profiles of 50 field isolates and 13 attenuated vaccine isolates did not match profiles of the 16 somatic type reference strains. Twenty-five DNA fingerprint profiles were recognized from 30 of these field isolates. The DNA fingerprint profiles of 20 field isolates and 13 attenuated vaccine isolates were identical. Three somatic types (3; 3,4; and 4,16) were identified from the field isolates, and two somatic types (3 and 3,4) were identified from the attenuated vaccine isolates. DNA fingerprinting is useful for accurate identification and epidemiologic study of P. multocida isolates.

Animals↗
PubMed1993

Stimulus speed and order of presentation effect the visually released predatory behaviors of the praying mantis Sphodromantis lineola (Burr.).

To assess the role of stimulus speed and order on the predatory behaviors of the praying mantis Sphodromantis lineola (Burr.), tethered adult females were presented with various flat black stimuli (lures) by means of a variable speed mechanical arm. Lure speed had a dramatic effect on mantis behavior: mantises emitted significantly more strikes to a 6 x 6 mm square and to 'worm' lures (i.e. length > width = 6 mm) moving at 34.3 cm/sec than they did to 'antiworm' lures (i.e. width > length = 6 mm), or to slower moving lures. These effects were consistent over lure directions (0-75 degrees relative to the mantis' long axis), and background patterns. On the other hand, mantises emitted significantly more approaching behavior to lures moving at 12 cm/sec than to lures moving at 36 cm/sec. This suggests that S. lineola extract distance information from retinal image velocity, as do other insects. Stimulus order also effected mantis predatory behavior: for instance, mantises were more likely to track a lure without striking at it on the first trial than on subsequent trials. However, after the first trial, they were also more likely to freeze (become immobile) when a lure was presented. Mantises were also less likely to strike at a preferred lure if it was preceded by one or two non-preferred lures. In a final experiment, intact, freely moving mantises were placed in an arena, presented with adult crickets, and video taped. The behaviors of the freely moving mantises were congruent with those of the tethered mantises in the previous experiments. This series of experiments demonstrates that the information processing capabilities of S. lineola are more complex than generally depicted, however, they can be explained by assuming a neural organization similar to that of other insects such as flies (Diptera) and dragonflies (Odonata).

Animals↗
PubMed1993

A worldwide survey of the teaching of glass ionomer (polyalkenoate) cements.

This paper reports the findings of a worldwide survey of the teaching of glass ionomer (polyalkenoate) cements (GICs). A total of 324 questionnaires was returned from the 650 dental schools included in the study (50 per cent response), with the response ranging from 100 per cent (Australasia) to 4 per cent (USSR). The findings indicate that most primary dental degree students in the majority of countries investigated are presently taught the use of GICs in a wide range of applications using techniques which largely conform with those recommended by the manufacturers of such materials.

Africa↗