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Biomedical subjects

S A Jones

Publications and source records attributed to S A Jones.

At least 109 records · Page 6Linked to original sources
PubMed1993

Nonadrenergic noncholinergic autonomic mediation of pressor response to feeding in lambs.

We examined factors mediating a 70% increase in arterial blood pressure that occurs during feeding in newborn lambs. We report that the increase in blood pressure during feeding was significantly reduced (to approximately 50%) and delayed in onset by combined alpha- and beta-adrenergic blockade. Plasma angiotensin and vasopressin levels did not increase significantly during feeding, nor was the pressor response to feeding attenuated while using captopril to block the production of angiotensin II. Adrenalectomy or muscarinic cholinergic blockade with atropine was also unsuccessful in attenuating the pressor response to feeding. We demonstrated that the component of the pressor response to feeding that was insensitive to alpha, beta, and muscarinic blockade was mediated by the autonomic nervous system because it was completely eliminated by ganglionic blockade with hexamethonium. Thus nonadrenergic noncholinergic autonomic mechanisms mediate approximately half the pressor response to feeding in lambs.

Adrenal Glands↗
PubMed1993

Fundamental sources of error and spectral broadening in Doppler ultrasound signals.

Analysis of the signals, spectra and error bounds for Doppler ultrasound signals is challenging and involves numerous concepts in signal analysis, probability, acoustics, and fluid mechanics. Nonetheless, the results of this analysis must be accessible to both engineers and clinicians who work with ultrasound technology. The engineer who designs, builds, or maintains equipment must know whether specific artifacts are fundamental or can be eliminated. The clinician must be able to interpret whether specific signal features accurately represent the flow field or result from limitations of Doppler ultrasound. This article reviews recent advances in both conceptual and numerical models of the Doppler ultrasound process, and relates these advances to practical aspects such as spectral broadening, velocity estimation error, and data analysis error. It then reviews recent innovations in system implementation and signal analysis which are indicative of the future potential of Doppler ultrasound instrumentation.

Artifacts↗
PubMed1992

Simulation of Doppler ultrasound signals for a laminar, pulsatile, nonuniform flow.

A simulation for Doppler ultrasound quadrature signals from pulsatile, nonuniform flow is presented. It is an extension of an earlier simulation presented by Jones and Giddens (1990a) which was valid for laminar, uniform, steady flow and which included the stochastic characteristics introduced by scattering particles which enter and leave the sample volume at random times. Fourier transform and autoregressive spectral analysis techniques are used to compare the simulated signals to Doppler signals collected from an in vitro flow setup. Power spectra, Doppler frequency estimates and standard deviations of these estimates serve as standards of comparison. Results show that the simulation model generates realistic quadrature signals. The study improves the understanding of the physics of the Doppler process and shows that it can be modeled for complex flow conditions. The input parameters of the simulation are the Doppler instrument parameters and flow characteristics. This allows the simulation to be used for transducer design as well as in the study of the applicability of signal analysis techniques to Doppler ultrasound.

Blood Flow Velocity↗
PubMed1991

Potentiation of mitomycin C and porfiromycin antitumor activity in solid tumor models by recombinant human interleukin 1 alpha.

The time- and dose-dependent effects of recombinant human interleukin 1 alpha (IL-1 alpha) on the antitumor activity of mitomycin C (MMC) and porfiromycin (PORF) were studied in RIF-1 and Panc02 solid tumor model systems. IL-1 alpha produced dose-dependent sensitization of clonogenic RIF-1 tumor cells to MMC in vivo. IL-1 alpha chemosensitization was highly schedule dependent, and the most efficacious schedules produced dose-modifying factors of 3.6 and 5.1 for MMC and PORF, respectively. More than additive clonogenic cell kill after IL-1 alpha-chemotherapy combinations reflected increased cellular sensitivity to MMC and PORF. The combinations also produced marked decreases in the yield of viable tumor cells, suggesting that the bioreductive drugs may have also potentiated the microvascular injury and ischemia produced by IL-1 alpha. Dexamethasone inhibited and ketoconazole, an inhibitor of corticosterone biosynthesis, enhanced IL-1 alpha-mediated chemosensitization in these models. IL-1 alpha mediated chemosensitization to MMC, and PORF was also demonstrated by tumor growth inhibition in the RIF-1 model and increased survival of mice in the spontaneously metastasizing Panc02 system. Chemosensitization of bone marrow spleen colony-forming units was not seen. IL-1 alpha (1000 units/ml) had no effect on MMC and PORF cytotoxicity in RIF-1 and PORF cell lines in vitro. The results indicate that the tumor-specific IL-1 alpha-induced pathophysiologies can sensitize solid tumors to agents which are preferentially activated, retained, and cytotoxic to cells under hypoxic conditions. Our results suggest that strategies combining bioreductively activated hypoxic cell cytotoxins and biological agents might offer efficacious alternatives or adjuvants to conventional combination approaches.

Animals↗
PubMed1991

The relationship between visual stimulation, behaviour and continuous release of protein in the substantia nigra.

In the substantia nigra, a protein (acetylcholinesterase) is secreted from the dendrites of dopaminergic pars compacta neurons, in a noncholinergic capacity. This non-classical phenomenon could be influenced by sensory stimulation: the effect of light flashing was investigated on the 'on-line' release of acetylcholinesterase and concomitant behaviour in the guinea-pig. The stimulus induced an increase in release of the protein and the appearance of chewing movements. Similarly, chewing could also be elicited by direct local application of exogenous acetylcholinesterase. The results suggest that visual stimulation causes release of AChE, which in turn facilitates movement. Therefore secretion of this protein within the substantia nigra might form an important intermediary step in visuo-motor interactions.

Acetylcholinesterase↗
PubMed1991

On the use of deuterium nuclear magnetic resonance as a probe of chain packing in lipid bilayers.

The packing of hydrocarbon chains in the bilayers of lamellar (L alpha) phases of soap/water and phospholipid/water mixtures has been studied by deuterium NMR spectroscopy and X-ray diffraction. A universal correlation is shown to exist between the average C-D bond order parameter SCD of hydrocarbon chains and the average area per chain ach, irrespective of the chemical structure of the surfactant (hydrophilic group, number of chains per molecule, and chain length), composition, and temperature. The practical utility of the correlation is illustrated by its application to the characterization of the distribution of various hydrophobic and amphiphilic solutes in bilayers. The distribution of hydrocarbons within a bilayer is shown to depend upon their molecular structure in a manner which highlights the nature of the molecular interactions involved. For example, benzene is shown to be fairly uniformly distributed across the bilayer with an increasing tendency to distribute into the center at high concentrations. In contrast, the more complex hydrocarbon tetradecane preferentially distributes into the center of the bilayer at low concentrations, while at higher concentrations it intercalates between the surfactant chains. Alcohols such as benzyl alcohol, octanol, and decanol all interact similarly with the bilayer in so far as they are pinned to the polar/apolar interface, presumably by involvement of the hydroxyl group in a hydrogen bond. But the response of the surfactant chains to the void volume created in the center of the bilayer is dependent upon the distance of penetration of the alcohol into the bilayer. For benzyl alcohol, the shortest molecule, this void volume is taken up by the disordering of the chains, while for decanol, the longest molecule, it is absorbed by interdigitation of the chains of apposing monolayers. For octanol, the chain interdigitation mechanism is dominant at low concentrations, but there is a transition to chain disordering at high concentrations. Finally, it is shown that the correlation provides a useful test for statistical mechanical models of chain ordering in lipid bilayers.

Deuterium↗
PubMed1991

Modern spectral analysis techniques for blood flow velocity and spectral measurements with pulsed Doppler ultrasound.

Four spectral analysis techniques were applied to pulsed Doppler ultrasonic quadrature signals to compare the relative merits of each technique for estimation of flow velocity and Doppler spectra. The four techniques were 1) the fast Fourier transform method, 2) the maximum likelihood method, 3) the Burg autoregressive algorithm, and 4) the modified covariance approach to autoregressive modeling. Both simulated signals and signals obtained from an in vitro flow system were studied. Optimal parameter values (e.g., model orders) were determined for each method, and the effects of signal-to-noise ratio and signal bandwidth were investigated. The modern spectral analysis techniques were shown to be superior to Fourier techniques in most circumstances, provided the model order was chosen appropriately. Robustness considerations tended to recommend the maximum likelihood method for both velocity and spectral estimation. Despite the restrictions of steady laminar flow, the results provide important basic information concerning the applicability of modern spectral analysis techniques to Doppler ultrasonic evaluation of arterial disease.

Algorithms↗
PubMed1991

Critical thinking: impact on nursing education.

Critical thinking is considered an essential component of nursing science. As a concept in nursing education, however, critical thinking is not clearly understood nor systematically applied. A survey of deans and directors of baccalaureate and higher-degree schools of nursing accredited by the National League for Nursing examined perceptions of critical thinking as it is currently characterized in nursing education. Results indicated that critical thinking was conceptualized as a variant of the scientific method. It was explicated as a rational-linear problem-solving activity which reflected the nursing process. The findings demonstrated the respondents' lack of clarity about the fullest expression of the mechanisms and operations of critical thinking process and applications.

Education, Nursing, Baccalaureate↗
PubMed1991

Behavioural correlates of the release and subsequent action of acetylcholinesterase secreted in the substantia nigra.

Acetylcholinesterase is secreted in the central nervous system (independently of cholinergic transmission) in a non-classic, non-enzymatic capacity. A light-emitting reaction has recently been established that demonstrates release of this protein from the substantia nigra of a guinea pig with a temporal resolution corresponding to real time, i.e. 'on-line'. In this study the technique has been applied to investigate the significance of this novel phenomenon in the generation of specific types of movement. During locomotion a 'pulsatile' release of acetylcholinesterase occurs much more frequently than in other situations. However, these pulses of released acetylcholinesterase are of shorter duration than the respective periods of locomotion that caused them. Furthermore, as episodes of movement are repeated, the release of acetylcholinesterase becomes less likely. These observations suggest that the phenomenon does not simply reflect ongoing movement. Indeed, chewing behaviour is frequently initiated when acetylcholinesterase release occurs during locomotor activity. Hence, acetylcholinesterase released in association with locomotion may favour the onset of further types of movement.

Journal Article↗
PubMed1990

A simulation of transit time effects in Doppler ultrasound signals.

A signal model is proposed which can be used to study frequency extraction techniques for Doppler ultrasound. The signal is based on the physics of the Doppler process and depends on a sliding window used to average a set of independent Gaussian random numbers. This window is related to the shape of the sample volume for the Doppler pulse and depends on the Doppler angle. Simulation results compare favorably with results from flow experiments in terms of the variance of the estimated Doppler shift, the shape of the power spectra and the behavior of the signals with respect to Burg autoregressive power spectra. A potential use of the signal in the study of spectral analysis techniques is presented.

Models, Theoretical↗
PubMed1990

"On-line" measurement of acetylcholinesterase release from the substantia nigra of the freely-moving guinea-pig.

Acetylcholinesterase is released from dopaminergic cells within the substantia nigra. The functional significance of this phenomenon has been studied in the freely-moving animal by a novel system for measuring acetylcholinesterase release from the substantia nigra "on-line" and in vivo. In the unanaesthetized guinea-pig the amount of acetylcholinesterase released was significantly greater than during anaesthesia, and release occurred in a more pulsatile manner. In addition, release of acetylcholinesterase could be evoked by either pharmacological or physiological manipulations, i.e. (1) a depolarizing concentration of potassium ions administered locally; (2) metamphetamine, administered systematically, which also resulted in increased locomotor activity; (3) drinking behaviour, elicited by presentation of a water bottle. Although all three treatments were accompanied by an increase in acetylcholinesterase release within the substantia nigra, potassium-evoked release did not cause any detectable change in behaviour. It is therefore suggested that release of the protein acetylcholinesterase within the substantia nigra is not necessarily a direct cause of locomotor activity: rather, it reflects diverse sensorimotor events.

Acetylcholinesterase↗
PubMed1990

Effects of corticotropin-releasing hormone and adrenocorticotropin on prostaglandin output by human placenta and fetal membranes.

We have examined the possibility that corticotropin-releasing hormone (CRH) and adrenocorticotropin (ACTH) might affect prostaglandin (PG) E2 and PGF2 alpha output by term placenta, amnion and decidua during short-term (48-hour) culture, and that effects of CRH might be mediated by ACTH. In all three tissues PG output was stimulated by both CRH and ACTH. These effects were inhibited in the presence of antisera to CRH and to ACTH. Moreover, in placenta, but not in amnion or decidua, the stimulatory effects of CRH on PGE2 and PGF2 alpha output were attenuated in the presence of an antibody to ACTH. Our results support the possibility of paracrine stimulation by CRH and ACTH of PG production in intrauterine tissues, and suggest that in part the effects of CRH on placental PG output might be mediated through ACTH.

Adrenocorticotropic Hormone↗
PubMed1990

Changes in glucocorticoid receptor number in the hypothalamus and pituitary of the sheep fetus with gestational age and after adrenocorticotropin treatment.

The concentrations of ACTH and cortisol both rise in the plasma of fetal lambs during late pregnancy, reflecting maturation of the fetal hypothalamic-pituitary-adrenal axis and providing the stimulus for parturition. The failure of rising cortisol to suppress plasma ACTH may be due to altered sensitivity of glucocorticoid negative feedback. To examine the possibility that this effect might be mediated through changes in the number of glucocorticoid receptors (GR) in the fetal hypothalamus and pituitary, we measured changes in GR number in these tissues from fetuses at discrete times of pregnancy between day 60 and term (day 145) and from newborn lambs and adult sheep. We also determined the effect of intrafetal ACTH administration in amounts known to produce premature parturition on GR number in fetuses at days 125-130 of gestation. Binding of [1,2,4-N-3H]triamcinolone acetonide to dispersed cell preparations of fetal pituitary and hypothalamus was saturable, temperature dependent, glucocorticoid specific, and of high affinity (2-3 X 10(-9) M). The number of GR in the pituitary always exceeded that in the hypothalamus. In both tissues GR number rose between days 60-70 to highest values on days 100-110, then decreased until day 125. GR number in the pituitary rose again at term, paradoxically at a time of rising endogenous glucocorticoid levels. However, after ACTH administration, there was a significant decrease in GR number in both hypothalamus and pituitary. These results indicate that altered efficacy of glucocorticoid negative feedback in term fetuses is not due to a decrease in pituitary or hypothalamic GR number. The rise in GR number at term and the fall after intrafetal ACTH treatment raises the possibility that mechanisms exist in the fetus allowing normal autoregulation of GR to be overridden at term.

Adrenocorticotropic Hormone↗
PubMed1990

Steroid, corticotrophin-releasing hormone, ACTH and prostaglandin interactions in the amnion and placenta of early pregnancy in man.

Corticotrophin-releasing hormone (CRH) is produced by both the placenta and fetal membranes at term in man, and CRH mRNA has been detected in human placental tissue. The synthesis of CRH and its control during early pregnancy, however, have not been established, and the role of CRH produced in the placenta and fetal membranes is not known. We examined whether amnion and placental tissue obtained between 12 and 15 weeks of gestation produced CRH in vitro, whether steroid modulation of output occurred and whether CRH affected prostaglandin (PG) output by the placenta and amnion. Immunoreactive (ir) CRH output by amnion (2.8 +/- 0.31 (S.E.M.) nmol/10(5) cells) was significantly (P less than 0.01) greater than that from placenta (1.76 +/- 0.21 nmol/10(5) cells). Output of ir-CRH decreased in the presence of progesterone, but increased in the presence of cortisol and dexamethasone. There was no significant effect of progesterone or ir-CRH output by placental cells; however, ir-CRH output was increased in the presence of dexamethasone and cortisol. There was no significant effect of corticosterone on ir-CRH output by either amnion or placental cells. Both ACTH and CRH stimulated the output of PGE2 and PGF2 alpha by amnion cells. In contrast, there was no significant effect of PGE2 output by placental cells maintained in the presence of either human CRH or ACTH. Output of PGF2 alpha by placental cells was increased in the presence of both CRH and ACTH. We conclude that both amnion and placental tissue produce CRH in early gestation, and that this output is modulated by steroids.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗
PubMed1990

Resin-bonded palatal stops for the management of a deep traumatic overbite--a case report.

This case presents a novel application of adhesive technology to treat a deep traumatic overbite in a patient unable to tolerate a removable appliance. Cast metal shelves were bonded into palatal surfaces of the upper anterior teeth. Three lower incisors required post crowns which were proclined slightly to engage the palatal stops of the upper teeth. After 24 months the palatal stops were firm and the occlusion seemed stable.

Acrylic Resins↗
PubMed1990

Replacement of missing maxillary canines by resin-bonded bridgework.

This report describes the replacement of both upper canine teeth in a young woman patient by means of resin-bonded bridges. While essentially simple, this case demonstrates the importance of careful assessment and planning to achieve the best potential for long-term success.

Adult↗