Biomedical subjects

R A Fox

Publications and source records attributed to R A Fox.

At least 37 records · Page 2Linked to original sources

PubMed1999

Can current models explain the lack of liver complications in Y-90 microsphere therapy?

Normal liver complications have not been observed in Y-90 microsphere therapy of hepatic tumors [selective internal radiation (SIR)], despite clinical studies reporting estimated absorbed doses to normal liver between 100 and 150 Gy. The purpose of the study was to see whether predictions of normal tissue complication probability (NTCP) models for liver based on clinical data from external beam therapy are consistent with clinical results of SIR. Liver NTCP was calculated using a parallel architecture model and normal liver dose-volume histograms that have been proposed for SIR. A parallel model including internal functional subunit structure is also proposed. Dose rate effects are incorporated. A criterion for comparing model calculations with clinical data is presented. For the parallel architecture model, the predicted NTCP is sensitive to the dose distribution in normal liver and to the model parameters, particularly the repair time. With reasonable assumptions about the microsphere distribution, the parallel model with parameters deduced from external beam therapy outcome analysis is consistent with the observed lack of liver complications. Inclusion of FSU structure widens the range of assumptions under which consistency is found. The parallel model can be consistent with the clinically observed lack of liver complications in SIR. More information about the activity distribution and the radiobiology of normal liver under conditions typical of microsphere therapy should be sought.

Humans↗

PubMed1998

Hypergravity exposure decreases gamma-aminobutyric acid immunoreactivity in axon terminals contacting pyramidal cells in the rat somatosensory cortex: a quantitative immunocytochemical image analysis.

Quantitative evaluation of gamma-aminobutyric acid immunoreactivity (GABA-IR) in the hindlimb representation of the rat somatosensory cortex after 14 days of exposure to hypergravity (hyper-G) was conducted by using computer-assisted image processing. The area of GABA-IR axosomatic terminals apposed to pyramidal cells of cortical layer V was reduced in rats exposed to hyper-G compared with control rats, which were exposed either to rotation alone or to vivarium conditions. Based on previous immunocytochemical and behavioral studies, we suggest that this reduction is due to changes in sensory feedback information from muscle receptors. Consequently, priorities for muscle recruitment are altered at the cortical level, and a new pattern of muscle activity is thus generated. It is proposed that the reduction observed in GABA-IR of the terminal area around pyramidal neurons is the immunocytochemical expression of changes in the activity of GABAergic cells that participate in reprogramming motor outputs to achieve effective movement control in response to alterations in the afferent information.

Animals↗

PubMed1998

Effects of microgravity on muscle and cerebral cortex: a suggested interaction.

The "slow" antigravity muscle adductor longus was studied in rats after 14 days of spaceflight (SF). The techniques employed included standard methods for light microscopy, neural cell adhesion molecule (N-CAM) immunocytochemistry and electron microscopy. Light and electron microscopy revealed myofiber atrophy, segmental necrosis and regenerative myofibers. Regenerative myofibers were N-CAM immunoreactive (N-CAM-IR). The neuromuscular junctions showed axon terminals with a decrease or absence of synaptic vesicles, degenerative changes, vacant axonal spaces and changes suggestive of axonal sprouting. No alterations of muscle spindles was seen either by light or electron microscopy. These observations suggest that muscle regeneration and denervation and synaptic remodeling at the level of the neuromuscular junction may take place during spaceflight. In a separate study, GABA immunoreactivity (GABA-IR) was evaluated at the level of the hindlimb representation of the rat somatosensory cortex after 14 days of hindlimb unloading by tail suspension ("simulated" microgravity). A reduction in number of GABA-immunoreactive cells with respect to the control animals was observed in layer Va and Vb. GABA-IR terminals were also reduced in the same layers, particularly those terminals surrounding the soma and apical dendrites of pyramidal cells in layer Vb. On the basis of previous morphological and behavioral studies of the neuromuscular system after spaceflight and hindlimb suspension it is suggested that after limb unloading there are alterations of afferent signaling and feedback information from intramuscular receptors to the cerebral cortex due to modifications in the reflex organization of hindlimb muscle groups. We propose that the changes observed in GABA immunoreactivity of cells and terminals is an expression of changes in their modulatory activity to compensate for the alterations in the afferent information.

Animals↗

PubMed1998

Study of adaptation to altered gravity through systems analysis of motor control.

Maintenance of posture and production of functional, coordinated movement demand integration of sensory feedback with spinal and supra-spinal circuitry to produce adaptive motor control in altered gravity (G). To investigate neuroplastic processes leading to optimal performance in altered G we have studied motor control in adult rats using a battery of motor function tests following chronic exposure to various treatments (hyper-G, hindlimb suspension, chemical distruction of hair cells, space flight). These treatments differentially affect muscle fibers, vestibular receptors, and behavioral compensations and, in consequence, differentially disrupt air righting, swimming, posture and gait. The time-course of recovery from these disruptions varies depending on the function tested and the duration and type of treatment. These studies, with others (e.g., D'Amelio et al. in this volume), indicate that adaptation to altered gravity involves alterations in multiple sensory-motor systems that change at different rates. We propose that the use of parallel studies under different altered G conditions will most efficiently lead to an understanding of the modifications in central (neural) and peripheral (sensory and neuromuscular) systems that underlie sensory-motor adaptation in active, intact individuals.

Adaptation, Physiological↗

PubMed1998

A simple phantom to locate the origin of MRI ghost artefacts.

A simple pyramidal tube phantom has been designed to allow accurate location of a selected slice along the desired axis of a magnetic resonance scanner and to provide a check of the quality of slice selection. It is particularly helpful in locating the origin of any out-of-slice ghost artefacts. The geometry of the phantom allows the slice positions to be calculated readily.

Artifacts↗

PubMed1998

Parental discipline and behavior problems in young children.

The relationship between parenting practices and behavior problems in very young children was investigated via the Parent Behavior Checklist (PBC; Fox, 1994). Results indicated that parents' use of verbal and corporal punishment was the strongest predictor of reported behavior problems, accounting for 20% of overall variance and 13% of unique variance. Results for parental nurturing and expectations were mixed and suggest an indirect effect. Several demographic variables were also predictive of behavior problems. Implications for Patterson's (1986) model of the development of antisocial behavior and for the use of parent assessment as a screening tool for preventive interventions are discussed.

Age Factors↗

PubMed1998

Evaluating a brief parental-education program for parents of young children.

The effectiveness of a brief parental-education program for 40 families with very young children was studied. Families were assigned to either a parental-education or waiting-list control group. The parental-education program included information and strategies drawn from developmental and cognitive psychology and social learning theory. Analysis showed that participating parents significantly reduced their use of corporal and verbal punishment, changed their parenting attitudes, and improved their perceptions of their children's behavior in comparison to the control group. Effects were maintained at six weeks follow-up. Results supported tailoring parental-education programs to the unique needs of participants.

Adult↗

PubMed1998

Comprehensive geriatric assessment. Helping your elderly patients maintain functional well-being.

In this article, three geriatricians describe an approach to comprehensive geriatric assessment that takes into account the multiple social and medical problems that affect the functional well-being of frail elderly patients. With a 45- to 90-minute time investment, physicians can obtain an inventory of the factors that threaten an elderly patient's independence and gain a fuller understanding of the patient's complex needs.

Aged↗

PubMed1997

Light microscopic image analysis system to quantify immunoreactive terminal area apposed to nerve cells.

The present report describes a desktop computer-based method for the quantitative assessment of the area occupied by immunoreactive terminals in close apposition to nerve cells in relation to the perimeter of the cell soma. This method is based on Fast Fourier Transform (FFT) routines incorporated in NIH-Image public domain software. Pyramidal cells of layer V of the somatosensory cortex outlined by GABA immunolabeled terminals were chosen for our analysis. A Leitz Diaplan light microscope was employed for the visualization of the sections. A Sierra Scientific Model 4030 CCD camera was used to capture the images into a Macintosh Centris 650 computer. After preprocessing, filtering was performed on the power spectrum in the frequency domain produced by the FFT operation. An inverse FFT with filter procedure was employed to restore the images to the spatial domain. Pasting of the original image to the transformed one using a Boolean logic operation called 'AND'ing produced an image with the terminals enhanced. This procedure allowed the creation of a binary image using a well-defined threshold of 128. Thus, the terminal area appears in black against a white background. This methodology provides an objective means of measurement of area by counting the total number of pixels occupied by immunoreactive terminals in light microscopic sections in which the difficulties of labeling intensity, size, shape and numerical density of terminals are avoided.

Animals↗

PubMed1997

Ligand linked assembly of Scapharca dimeric hemoglobin.

The assembly of Scapharca dimeric hemoglobin as a function of ligation has been explored by analytical gel chromatography, sedimentation equilibrium, and oxygen binding experiments to test the proposal that its cooperativity is based on quaternary enhancement. This hypothesis predicts that the liganded form would be assembled more tightly into a dimer than the unliganded form and that dissociation would lead to lower oxygen affinity. Our experiments demonstrate that although the dimeric interface is quite tight in this hemoglobin, dissociation can be clearly detected in the liganded states with monomer to dimer association constants in the range of 10(8) M-1 for the CO-liganded state and lower association constants measured in the oxygenated state. In contrast, the deoxy dimer shows no detectable dissociation by analytical ultracentrifugation. Thus, the more highly hydrated deoxy interface of this dimer is also the more tightly assembled. Equilibrium oxygen binding experiments reveal an increase in oxygen affinity and decrease in cooperativity as the concentration is lowered (in the muM range). These experiments unambiguously refute the hypothesis of quaternary enhancement and indicate that, as in the case of human hemoglobin and other allosteric proteins, quaternary constraint underlies cooperativity in Scapharca dimeric hemoglobin.

Animals↗

PubMed1997

Human immunodeficiency virus infection in systemic lupus erythematosus.

This report describes a female patient with systemic lupus erythematosus (SLE) who was infected with the human immunodeficiency virus (HIV). Using stored serum, the precise timing of HIV seroconversion was determined and the early effects of HIV infection on SLE examined. This infection resulted in clinical improvement and the disappearance of autoantibody production. A literature review of the association between HIV and SLE is provided.

Adult↗

PubMed1997

Parenting of young children by fathers in Mexico and the United States.

In the present study, the parenting practices and developmental expectations were examined in a sample of 96 fathers from Mexico and the United States, all with children from 1 to 5 years of age. The selection of fathers from both countries was controlled for the family's socioeconomic status (SES) and for the age and gender of their children. The Parent Behavior Checklist, a 100-item rating scale was used to measure parents' developmental expectations and their discipline and nurturing practices. According to the results, Mexican and U.S. fathers did not differ significantly in their developmental expectations or parenting practices. In both countries, fathers from lower SES families were less nurturing and used more frequent discipline than fathers from higher SES families.

Adult↗

PubMed1997

The use of anisotropic data in 125I prostate implants.

The report recently published by AAPM Task Group 43' (TG43) recommends the use of a two dimensional dose distribution function for the dosimetry associated with 125I, 192Ir and 103Pd sources. For commercial planning systems that cannot be readily adapted to use a two dimensional function, a point source approximation is provided. The dose distribution around an array of 125I seeds has been calculated using the two dimensional model and the point source approximation. Isodose distributions through selected planes and dose volume histograms of selected cubic volumes show that differences between the two models for this array are insignificant, particularly in view of the uncertainties associated with using the data which is provided by TG43 for the two dimensional anisotropy function.

Anisotropy↗

PubMed1997

Dosimetry of beta emitting radionuclides for use in balloon angioplasty.

The dose at varying distances from the surface of an infinite cylinder containing 90Y, 32P and 188Re respectively is calculated using published scaled point dose kernels for these three radionuclides. It is shown that all are suitable radionuclides for use in the irradiation of arteries subsequent to balloon angioplasty. All three may be used as a radioactive liquid in the angioplasty balloon, thereby simplifying the procedure and enabling a uniform radiation dose to be given to the arterial wall. It is however shown that there is a rapid reduction in dose with distance from the arterial wall which demands careful specification of the prescribed radiation dose. A similar rapid reduction with distance is also found with a central radioactive wire or with a radioactive stent containing the same radionuclides.

Angioplasty, Balloon↗

PubMed1996

Quantitative changes of GABA-immunoreactive cells in the hindlimb representation of the rat somatosensory cortex after 14-day hindlimb unloading by tail suspension.

The present study was aimed at evaluating quantitatively gamma-aminobutyric acid (GABA) immunoreactivity in the hindlimb representation of the rat somatosensory cortex after 14 days of hindlimb unloading by tail suspension. A reduction in the number of GABA-immunoreactive cells with respect to the control animals was observed in layer Va and Vb. GABA-containing terminals were also reduced in the same layers, particularly those terminals surrounding the soma and apical dendrites of pyramidal cells in layer Vb. On the basis of previous morphological and behavioral studies of the neuromuscular system of hindlimb-suspended animals, it is suggested that the unloading due to hindlimb suspension alters afferent signaling and feedback information from intramuscular receptors to the cerebral cortex due to modifications in the reflex organization of hindlimb muscle groups. We propose that the reduction in immunoreactivity of local circuit GABAergic neurons and terminals is an expression of changes in their modulatory activity to compensate for the alterations in the afferent information.

Animals↗

PubMed1996

Comparison of the stimulus properties of a pre- vs. a putative postsynaptic dose of quinpirole.

Presynaptic D2-like receptors appear to mediate the stimulus properties of a low dose (0.05 mg/kg) of the D2-like agonist quinpirole (QUIN), because treatments decreasing dopamine (DA) release or blocking postsynaptic DA receptor activation produce QUIN-appropriate responding in a drug discrimination context, whereas treatments activating postsynaptic DA receptors evoke saline responding (28). This study examined the hypothesis that training to a presumably postsynaptic dose of QUIN (0.20 mg/kg) would produce the opposite pattern of effects. Using drug discrimination procedures, substitution for 0.05 mg/kg (28), but not 0.20 mg/kg QUIN, was produced by the D1 antagonist SCH23390, the catecholamine depleter alpha-methyl-paratyrosine and low doses of apomorphine (up to 0.25 mg/kg). The D2 agonist NPA substituted fully for 0.05 but only partially for 0.20 mg/kg QUIN. Cocaine and d-amphetamine (alone or with SCH 23390) substituted only minimally for either QUIN training dose. The putative D3 agonist 7-OH-DPAT engendered primarily saline responding when substituted for 0.20 QUIN. The 0.20 QUIN stimulus was antagonized by the D2 blocker haloperidol and partially blocked by the D1 antagonist SCH 23390. These data show a clear difference in the mediation of the stimulus properties of a low (0.05 mg/kg) vs. a high (0.20 mg/kg) dose of QUIN and are suggestive of a preferential postsynaptic D2 mediation of the 0.20 mg/kg QUIN dose.

Animals↗

PubMed1996

Neuroendocrine changes in systemic lupus erythematosus and Sjögren's syndrome.

It has become clear that the neuroendocrine and immune systems are closely linked and interdependent. The exact mechanisms of this interaction are only beginning to be unravelled. The complexity of these connections may partly explain why the aetiopathogenesis of autoimmune diseases remains obscure and why genetic, hormonal, microbial, environmental, as well as a host of other factors, have all been put forward as explanations. What has become clear is that a number of neuroendocrine and hormonal factors have important immunomodulatory roles in health and disease.

Animals↗

PubMed1996

Parenting practices and expectations among Mexican mothers with young children.

Parenting practices and developmental expectations were examined in a sample of 221 Mexican mothers with very young children living in Guadalajara, Jalisco. They completed a Spanish version of the Parent Behavior Checklist (PBC), a 100-item rating scale that measures parents' developmental expectations, discipline, and nurturing practices. The psychometric properties of the PBC for Mexican mothers, including test-retest reliabilities, were very similar to those found for mothers of young children in the United States. Younger Mexican mothers used more frequent discipline and less nurturing with their young children than older mothers did. Married mothers nurtured their children more than unmarried mothers; young, unmarried mothers nurtured their children the least. Lower nurturing scores were associated with lower education levels, and higher nurturing scores were associated with higher education levels. Mothers from higher socioeconomic levels held higher developmental expectations for their children, and they used less frequent discipline and more frequent nurturing practices than mothers from lower socioeconomic levels. These findings are consistent with those for mothers of young children in the United States.

Adult↗