Biomedical subjects
Publications and source records attributed to D C Roberts.
We prove the finite-time collapse of a system of N classical fields, which are described by N coupled nonlinear Schrödinger equations. We derive the conditions under which all of the fields experiences this finite-time collapse. Finally, for two-dimensional systems, we derive constraints on the number of particles associated with each field that are necessary to prevent collapse.
We calculate a force due to zero-temperature quantum fluctuations on a stationary object in a moving superfluid flow. We model the object by a localized potential varying only in the flow direction and model the flow by a three-dimensional weakly interacting Bose-Einstein condensate at zero temperature. We show that this force exists for any arbitrarily small flow velocity and discuss the implications for the stability of superfluid flow.
We propose a method to probe states in the Mott insulator regime produced from a condensate in an optical lattice. We consider a system in which we create time-dependent number fluctuations in a given site by turning off the atomic interactions and lowering the potential barriers on a nearly pure Mott state to allow the atoms to tunnel between sites. We calculate the expected interference pattern and number fluctuations from such a system and show that one can potentially observe a deviation from a pure Mott state. We also discuss a method in which to detect these number fluctuations using time-of-flight imaging.
The three pairs of semicircular canals within the labyrinth are not perfectly aligned with the pulling directions of the six extraocular muscles. Therefore, for a given head movement, the vestibulo-ocular reflex (VOR) depends upon central neural mechanisms that couple the canals to the muscles with the appropriate functional gains in order to generate a response that rotates the eye the correct amount and around the correct axis. A consequence of these neural connections is a cross-axis adaptive capability, which can be stimulated experimentally when head rotation is around one axis and visual motion about another. From this visual-vestibular conflict the brain infers that the slow-phase eye movement is rotating around the wrong axis. We explored the capability of human cross-axis adaptation, using a short-term training paradigm, to determine if torsional eye movements could be elicited by yaw (horizontal) head rotation (where torsion is normally inappropriate). We applied yaw sinusoidal head rotation (+/-10 degrees, 0.33 Hz) and measured eye movement responses in the dark, and before and after adaptation. The adaptation paradigm lasted 45-60 min, and consisted of the identical head motion, coupled with a moving visual scene that required one of several types of eye movements: (1) torsion alone (-Roll); (2) horizontal/torsional, head right/CW torsion (Yaw-Roll); (3) horizontal/torsional, head right/CCW torsion (Yaw+Roll); (4) horizontal, vertical, torsional combined (Yaw+Pitch-Roll); and (5) horizontal and vertical together (Yaw+Pitch). The largest and most significant changes in torsional amplitude occurred in the Yaw-Roll and Yaw+Roll conditions. We conclude that short-term, cross-axis adaptation of torsion is possible but constrained by the complexity of the adaptation task: smaller torsional components are produced if more than one cross-coupling component is required. In contrast, vertical cross-axis components can be easily trained to occur with yaw head movements.
An 8-week-old piglet with dyspnoea, bilateral mucopurulent nasal discharge and mouth breathing was euthanased and a necropsy was performed. Apart from histological evidence of diffuse rhinitis, large intranuclear inclusion bodies, pathognomonic forporcine cytomegalovirus infection, were detected within mucous glands on the nasal turbinates. This is the first such case to be diagnosed in South Africa.
The GM-CSF gene is expressed following activation of T cells. The proximal promoter and an upstream enhancer have previously been characterized using transfection and reporter assays in T cell lines in culture. A 10.5-kb transgene containing the entire human GM-CSF gene has also been shown to display inducible, position-independent, copy number-dependent transcription in mouse splenocytes. To determine the role of individual promoter elements in transgene function, mutations were introduced into the proximal promoter and activity assessed following the generation of transgenic mice. Of four mutations introduced into the transgene promoter, only one, in an NF-kappaB/Sp1 region, led to decreased induction of the transgene in splenocytes or bone marrow-derived macrophages. This mutation also affected the activity of reporter gene constructs stably transfected into T cell lines in culture, but not when transiently transfected into the same cell lines. The mutation alters the NF-kappaB family members that bind to the NF-kappaB site as well as reducing the binding of Sp1 to an adjacent element. A DNase I hypersensitive site that is normally generated at the promoter following T cell activation on the wild-type transgene does not appear in the mutant transgene. These results suggest that the NF-kappaB/Sp1 region plays a critical role in chromatin remodeling and transcription on the GM-CSF promoter in primary T cells.
RATIONALE: Rats exhibit marked individual differences in consumption of freely available sucrose; however, the underlying mechanism(s) contributing to such interindividual differences remain unclear. OBJECTIVES: The current study examined whether: 1) motivational differences (as reflected by the degree of operant output to procure sucrose reward) underlie variability in sugar consumption, and 2) whether potential differences in dopaminergic and/or opioidergic systems contribute to such differences. METHODS: In the initial experiment, Sprague-Dawley rats were divided into those that spontaneously consumed High or Low amounts of sucrose, based on the consumption of freely available sugar (+/-2 SD from group median) over 7 consecutive test days. The potential differences in their motivation to seek and "earn" sucrose solution rewards were measured using the progressive ratio (PR) schedule of reinforcement. RESULTS: Performance of both groups on the PR schedule was sensitive to the concentration of sucrose (i.e. the higher the concentration, the greater the behavioral output). Furthermore, the High sucrose consumers earned a greater number of reinforcements (20% sucrose solution) than the Low group. Parenthetically, the degree of behavioral output by the High (but not the Low) group was comparable to that emitted for water under water-deprived condition. Treatment with the opioid antagonist, naloxone, attenuated PR performance for sucrose, whereas d-amphetamine (0.5 mg/kg) enhanced it. Furthermore, naloxone attenuated amphetamine-enhanced responding for sucrose reward, suggesting an interaction between the dopaminergic and opioidergic systems in the mediation of sucrose reward. CONCLUSIONS: These results support the contention that motivational differences may partially account for individual variability in sucrose consumption, and that dopaminergic and/or opioidergic agents differentially affect the "wanting" and/or "liking" of sucrose in the High and Low sucrose consumers.
Chronic cocaine use is known to elicit changes in the pattern of gene expression within the brain. The hippocampus plays a critical role in learning and memory and may also play a role in mediating behaviors associated with cocaine abuse. To profile the gene expression response of the hippocampus to chronic cocaine treatment, cDNA hybridization arrays were used to illuminate cocaine-regulated genes in rats treated non-contingently with a binge model of cocaine (45 mg/kg/day, i.p.) for 14 days. Validation of mRNA changes illuminated by hybridization array analysis was accomplished by measuring immunoreactive protein (via specific immunoblots). The induction of protein kinase Calpha, potassium channel 1.1, and metabotropic glutamate receptor 5 seen by hybridization arrays was confirmed at the level of protein. Immunoblot screening of previously described cocaine-responsive genes demonstrated increased levels of protein tyrosine kinase 2, beta-catenin, and protein kinase Cepsilon. While some of these changes exist in previously described cocaine-responsive models, others are novel to any model of cocaine use. The inductions of potassium channel 1.1, protein tyrosine kinase 2 and metabotropic glutamate receptor 5 are novel findings to hippocampal cocaine-responsive gene expression. These proteins have been shown to subserve learning and memory and/or long-term potentiation functions within the hippocampus. Additionally, these genes are known to interact with one another, forming a more complex pattern of gene expression changes. The findings suggest altered expression of genes with a number of different functions in the rat hippocampus after a 'binge' style of non-contingent cocaine administration. These changes in gene expression may play roles in neuronal plasticity and the behavioral phenomena associated with cocaine abuse.
OBJECTIVE: To examine the effects of iron deficiency and its treatment by iron supplementation or a high iron diet on fatigue and general health measures in women of childbearing age. DESIGN: Randomised controlled trial to compare supplement and dietary treatment of iron deficiency. SUBJECTS: 44 iron deficient (serum ferritin < 15 microg/L or serum ferritin 15-20 microg/L, plus two of the following: serum iron < 10 micromol/L, total iron binding capacity > 68 micromol/L or transferrin saturation < 15%) and 22 iron replete (hemoglobin > or = 10 g/L and serum ferritin > 20 microg/L) women 18 to 50 years of age were matched for age and parity. INTERVENTIONS: Iron deficient women were randomly allocated to either iron supplementation or a high iron diet for 12 weeks. MEASURES OF OUTCOME: Iron deficient and iron replete participants had iron studies performed and completed the Piper Fatigue Scale (PFS) and the SF-36 general health and well-being questionnaire at baseline (T0), following the 12 week intervention (T1) and again after a six-month non-intervention phase (T2). The SF-36 includes measures of physical (PCS) and mental (MCS) health and vitality (VT). RESULTS: MCS and VT scores were lower and PFS scores were higher for iron deficient women (diet and supplement groups) than iron replete women at baseline. Both intervention groups showed similar improvements in MCS, VT and PFS scores during the intervention phase, but mean increases in serum ferritin were greater in the supplement than the diet group. PCS scores were not related to iron status. CONCLUSIONS: Treatment of iron deficiency with either supplementation or a high iron diet results in improved mental health and decreased fatigue among women of childbearing age.
BACKGROUND: The Australian Iron Status Advisory Panel advocates dietary intervention as the first treatment option for mild iron deficiency [serum ferritin (SF) = 10-15 microg/L]. However, there appear to be no studies on the efficacy of dietary treatment for iron deficiency. OBJECTIVE: We compared the effects of iron supplementation and of a high-iron diet on serum ferritin (SF) and hemoglobin in iron-deficient women of childbearing age. DESIGN: Forty-four iron-deficient women (SF <15 microg/L or SF = 15-20 microg/L plus serum iron <10 micromol/L and total-iron-binding capacity >68 micromol/L) and 22 iron-replete women (hemoglobin > or =120 g/L and SF >20 microg/L) matched for age and parity categories were enrolled and completed 7-d weighed food records at baseline. The iron-deficient women were randomly allocated to receive iron supplementation (105 mg/d; supplement group) or a high-iron diet (recommended intake of absorbable iron: 2.25 mg/d; diet group) for 12 wk. Hematologic and dietary assessments were repeated at the end of the intervention and again after a 6-mo follow-up. RESULTS: Mean SF in the supplement group increased from 9.0 +/- 3.9 microg/L at baseline to 24.8 +/- 10.0 microg/L after the intervention and remained stable during follow-up (24.2 +/- 9.8 microg/L), whereas the diet group had smaller increases during the intervention (8.9 +/- 3.1 to 11.0 +/- 5.9 microg/L) but continued to improve during follow-up (to 15.2 +/- 9.5 microg/L). Mean hemoglobin tended to improve in both intervention groups, but the change was only significant in the supplement group. CONCLUSIONS: In iron-deficient women of childbearing age, a high-iron diet produced smaller increases in SF than did iron supplementation but resulted in continued improvements in iron status during a 6-mo. follow-up.
The purpose of this phenomenological study was to discover, describe, and understand the lived experience of some of Maine's most isolated elder women, those living alone on islands off the coast. Nine women, age 80 and older, were interviewed. Three dominant themes essential to this rural island lifeway emerged: no one is an island, no one lives alone; securely anchored in safe harbor; and weathering the storms. Results were that these women remain actively engaged in life, feeling valued and connected, safe and secure; they are resourceful, resilient, and determined.
PURPOSE: To establish an objective Hess screen test that allows a simultaneous and binocular analysis of all three axes of eye rotation. METHODS: In orthotropic and strabismic human subjects, both eyes were recorded with dual scleral search coils in a three-field magnetic system. Before mounting the search coil annuli on the eyes, the voltage offsets of each channel and the relative magnitudes of the three magnetic fields were determined. For calibration, subjects were only required to fix monocularly on a single reference target. During fixation of targets on the Hess screen by the uncovered eye, the three-dimensional eye position of both the occluded and the viewing eye was simultaneously measured. RESULTS: For clinical interpretation, an easy to understand graphical description of the three-dimensional Hess screen test was developed. Positions of orthotropic and strabismic eyes tended to follow Listing's law, which in both eyes allowed the determination of the primary position, that is, the position of gaze from which pure horizontal and pure vertical movements do not lead to an ocular rotation about the line-of-sight. To a first approximation, the location of primary position is a result of the summation of the individual rotation axes of the six extraocular muscles and thus can be used to infer which muscle is paretic. CONCLUSIONS: The three-dimensional Hess screen test with binocular dual search coils in a three-field magnetic system is an objective method to assess the ocular alignment in three dimensions with high precision. From these recordings, the clinician can relate deviations of primary position to specific eye muscle palsies.
The World Health Organisation has restructured their program for health and the elderly, renaming it Aging and Health, focussing on aging as a part of life rather than a static age group separated from the rest of the population. As the older population becomes more heterogeneous, nutrition and food service providers in the community are faced with new challenges. This paper presents nutrition recommendations relevant to community nutrition programs in Australia including the recently released Dietary Guidelines for Older Australians. The subsequent discussion focuses on issues associated with implementation of community based food and nutrition intervention programs. The following strategies for successful implementation of community based food and nutrition programs were identified: Meals on Wheels services. 1. should maintain a register of food service systems for each site to assist in the planning process. 2. Develop a procedure for the nutritional assessment of menus focussing on a standardised methodology and recipes as well as ensuring trained staff are available to apply the procedure. 3. Validate recommended serving sizes and recommend serving utensils for specific menu items. Provide advice on the purchasing, use and calibration of scales as well as containers. 4. Develop alternative, informal methods of assessing client satisfaction to ensure the clients' experience with the service, rather than their reaction to the experience, be assessed. 5. Develop a management training program which focuses on a "train-the-trainer' strategy to ensure continuous, on-site training. Meeting the nutritional needs of the heterogeneous group of older people implies a modified approach to nutritional support. All those involved in community nutrition organisations need to recognise the significance of the "caring" role as well as that of food provider and the impact of this on the nutritional status of the client. The development of consistent guidelines and tools will assist organisations in meeting the needs of their target groups. As professionals we need to understand and accept the constraints that these organisations deal with to ensure the services we provide are appropriate. These constraints include all of those issues detailed in this paper - production capability, training resources and the availability of volunteers.
Countries that have made the health transition from a communicable disease base to a non-communicable disease base find themselves gripped in an epidemic of wealth created diseases mediated by altered macronutrient intakes, energy intakes and reduction in physical activity. Avoiding the negative impact of the nutrition transition while accepting the positive aspects of the wealth transition can best be achieved by focussing on publicising the benefits of a low fat diet in the context of an active lifestyle. How this is achieved should reflect ecologically sound food production appropriate to national needs. Countries that achieve this will be in the best position to capitalize on the reduction in communicable disease rates without causing a rise in non-communicable disease rates.
RATIONALE: Recent reports have indicated that the gamma-aminobutyric acid (GABA)B agonist baclofen attenuates the reinforcing effects of cocaine. OBJECTIVES: To further evaluate the effect of baclofen on cocaine self-administration under a fixed ratio (FR) and progressive ratio (PR) schedule of reinforcement. METHODS: In the first series of experiments, three dose-response curves were generated that examined the effect of three doses of baclofen (1.8, 3.2, or 5.6 mg/kg, i.p.) against four unit-injection doses of cocaine (0.19, 0.38, 0.75, and 1.5 mg/kg per injection) reinforced under a FRI schedule. For comparison, an additional group of rats was pretreated with haloperidol (32, 56, or 100 microg/kg, i.p.). A separate experiment examined the effect of baclofen (1.8, 3.2, or 5.6 mg/kg, i.p.) on responding for concurrently available cocaine or food reinforcement. RESULTS: Under the FR1 schedule, baclofen suppressed intake of low but not high unit injection doses of cocaine. In contrast to haloperidol, baclofen had no effect on the distribution of inter-injection intervals and, instead, produced long pauses in cocaine self-administration. Baclofen dose dependently reduced cocaine-reinforced responding on a PR schedule; concurrent access to a food-reinforced lever demonstrated that the animals retained the capacity to respond at high rates. CONCLUSION: The effect of baclofen pretreatment on cocaine self-administration is dependent on the unit injection dose of cocaine and on the response requirements of the schedule.
UNLABELLED: To study motor and sensory responses in vertical fusion at different angles of horizontal vergence in normal humans. METHODS: The study included 12 normal subjects. A cross (+) extending 3.4 degrees x3.2 degrees was presented dichoptically. Vertical disparity was introduced by changing the vertical position of the cross in front of one eye. The disparity was incremented by 0.08 degrees every 8 s. Distance viewing was tested with 1 degrees of convergence demand, near vision with 6-15 degrees convergence demand. Eye movements were recorded using three-axis search coils. RESULTS: Vertical fusion capability was larger at near vision than at distance in 9 of 12 subjects. For the entire group, total vertical fusion capability (motor plus sensory response) differed between distance (mean 1.68 degrees ) and near (mean 2.39 degrees ). The motor component differed significantly between distance (mean 1.42 degrees ) and near (mean 2.13 degrees ). No difference in the sensory component was seen between distance (mean 0.26 degrees ) and near (mean 0.27 degrees ). CONCLUSIONS: Vertical fusion capability increases with convergence. This increase is mainly due to an increase of the motor response.
The effect of microinjections of baclofen into the ventral tegmental area (VTA), nucleus accumbens, or striatum on cocaine self-administration reinforced on a progressive ratio schedule was investigated. Intra-VTA baclofen produced the most potent modulation of cocaine intake, causing a significant reduction in cocaine-reinforced break points at a dose (56 ng/side) that was substantially lower than doses necessary to produce comparable reductions in the nucleus accumbens or striatum. During the time that cocaine-reinforced responding was suppressed, rats demonstrated the capacity to complete several hundred responses on a concurrently available food-reinforced lever, indicating that the effect of baclofen on cocaine intake was not due to a generalized disruption in operant responding. The results indicate that GABA(B) receptors in the VTA may have the potential to modulate reward processes associated with cocaine use.