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Biomedical subjects

D C Roberts

Publications and source records attributed to D C Roberts.

At least 37 records · Page 2Linked to original sources
PubMed2000

Iron deficiency, general health and fatigue: results from the Australian Longitudinal Study on Women's Health.

Associations between self-reported 'low iron', general health and well-being, vitality and tiredness in women, were examined using physical (PCS) and mental (MCS) component summary and vitality (VT) scores from the MOS short-form survey (SF-36). 14,762 young (18-23 years) and 14,072 mid-age (45-50 years) women, randomly selected from the national health insurance commission (Medicare) database, completed a baseline mailed self-report questionnaire and 12,328 mid-age women completed a follow-up questionnaire 2 years later. Young and mid-age women who reported (ever) having had 'low iron' reported significantly lower mean PCS, MCS and VT scores, and greater prevalence of 'constant tiredness' at baseline than women with no history of iron deficiency [Differences: young PCS = -2.2, MCS = -4.8, VT = -8.7; constant tiredness: 67% vs. 45%; mid-age PCS = -1.4, MCS = -3.1, VT = -5.9; constant tiredness: 63% vs. 48%]. After adjusting for number of children, chronic conditions, symptoms and sociodemographic variables, mean PCS, MCS and VT scores for mid-age women at follow-up were significantly lower for women who reported recent iron deficiency (in the last 2 years) than for women who reported past iron deficiency or no history of iron deficiency [Means: PCS--recent = 46.6, past = 47.8, never = 47.7; MCS--recent = 45.4, past = 46.9, never = 47.4; VT--recent = 54.8, past = 57.6, never = 58.6]. The adjusted mean change in PCS, MCS and VT scores between baseline and follow-up were also significantly lower among mid-age women who reported iron deficiency only in the last 2 years (i.e. recent iron deficiency) [Mean change: PCS = -3.2; MCS = -2.1; VT = -4.2]. The results suggest that iron deficiency is associated with decreased general health and well-being and increased fatigue.

Adolescent↗
PubMed2000

A review of the nutritional needs of Meals on Wheels consumers and factors associated with the provision of an effective meals on wheels service-an Australian perspective.

OBJECTIVE: A review of the literature was undertaken to identify the nutritional needs of elderly MOW consumers and factors affecting the ability of existing programs to meet those needs. The focus was on the Australian experience but drawing on the world literature. DESIGN: Keyword search of English language based computer databases of the medical and health literature. RESULTS: Several studies suggest the nutritional intake of MOW consumers is below recommended levels, although the risk of nutritional deficiency has not always been identified. The literature indicates the effectiveness of Meals on Wheels programs are affected by a range of issues including the appropriateness of nutritional standards, menu selection, portion control, level of consumption and customer satisfaction. The literature recommends control of time and temperatures associated with food handling procedures, along with education of providers and customers, to assist in the provision of a safe food supply. CONCLUSIONS: Meals on Wheels is an important service, providing meals to housebound consumers. While the effectiveness of such programs is dependent on a range of variables, the nutritional impact of the service and the standard of food hygiene are fundamental assessment criteria. SPONSORSHIP: This work was supported by a grant from the NSW Meals on Wheels Association, Australia. European Journal of Clinical Nutrition (2000) 54, 275-280

Aged↗
PubMed2000

Fish oil feeding enhances lymphocyte proliferation but impairs virus-specific T lymphocyte cytotoxicity in mice following challenge with influenza virus.

The effect of a fish oil diet on virus-specific cytotoxicity and lymphocyte proliferation was investigated. Mice were fed fish oil (17 g fish oil and 3 g sunflower/100 g) or beef tallow (17 g tallow and 3 g sunflower/100 g) diets for 14 days before intranasal challenge with influenza virus. At day 5 after infection, lung virus-specific T lymphocyte, but not macrophage or natural killer (NK) cell, cytotoxicity was significantly lower in mice fed fish oil, while bronchial lymph node cell proliferation to virus was significantly higher. In mice fed fish oil, spleen cell proliferation to virus was also significantly higher following immunization. The results showed that, despite improved lymphocyte proliferation, fish oil impairs primary virus-specific T lymphocyte cytotoxicity. This impairment may explain the delayed virus clearance that we have previously reported in infected mice fed the fish oil diet.

Animals↗
PubMed2000

GABA modulation of cocaine self-administration.

Recent experiments suggest that GABA compounds produce a clinically relevant modulation of cocaine reinforcement. This review summarizes the results of a number of studies that examined the effect of the GABAB agonist baclofen on cocaine self-administration using a variety of schedules of reinforcement. The results demonstrate that baclofen causes a dramatic reduction in cocaine self-administration which does not appear to be accounted for by a general disruption of behavior. However, the effect is dependent on the unit injection dose of cocaine and on the response requirements of the schedule. These results predict that in a clinical setting any potential therapeutic effect of baclofen will interact with the cost and availability of cocaine.

Animals↗
PubMed2000

Effect of sustained cyclovergence on eye alignment: rapid torsional phoria adaptation.

PURPOSE: To describe adaptive changes in torsional alignment that follow sustained cyclovergence in healthy humans. METHODS: Eye movements were recorded binocularly from four healthy subjects using dual-coil scleral annuli. Cyclovergence movements were evoked over periods of 30 to 150 seconds using a stereoscopic display, presenting gratings of lines arranged horizontally, vertically, or at 45 degrees, subtending angles of up to 48 degrees. In- and excyclodisparities of 5 degrees were introduced and removed in a single-step fashion. After stimulation, the time course and magnitude of the decay in cyclovergence was compared with the subject either in darkness or viewing a baseline stimulus of zero cyclodisparity. RESULTS: As reported previously, the cyclovergence response to incyclodisparities was greater than to excyclodisparities. After sustained excyclovergence, however, in all subjects and in response to all orientations of the gratings, the decay in darkness was incomplete, implying an adaptive change in torsional alignment. In response to the horizontal gratings, for incyclovergence there was also an incomplete decay in darkness but to a lesser degree than in response to excyclovergence, and in only three of four subjects. The incyclovergence evoked by the oblique and vertical gratings was of small magnitude, and its decay was unaffected by the presence or absence of a visual stimulus. CONCLUSIONS: After sustained cyclovergence, its decay in the absence of a visual stimulus may be incomplete. The residual component may be interpreted, by analogy with horizontal and vertical vergence, as reflecting so-called phoria adaptation for torsional alignment.

Adaptation, Ocular↗
PubMed2000

Dynamics of the human linear vestibulo-ocular reflex at medium frequency and modification by short-term training.

We study here the effect of a short-term training paradigm on the gain and phase of the human translational VOR (the linear VOR: LVOR). Subjects were exposed to lateral sinusoidal translations on a sled, at 0.5 Hz, 0.3 g peak acceleration. With subjects tracking a remembered target at 1.2 m, the LVOR (slow-phase) under these conditions typically has a phase lead or lag, and a gain that falls short of compensatory. To induce short-term adaptation (training), we presented an earth-fixed visual scene at 1.2 m during sinusoidal translation (x 1 viewing) for 20 minutes, so as to drive the LVOR toward compensatory phase and gain. We examined both the slow-phase and the saccadic responses to these stimuli. Testing after training showed changes in slow-component gain and phase which were mostly but not always in the compensatory direction. These changes were more consistent in naive subjects than in subjects who had previous LVOR experience. Changes in gain were seen with step as well as sinusoidal test stimuli; gain changes were not correlated with vergence changes. There was a strong correlation between gain changes and phase changes across subjects. Fast phases (catch-up saccades) formed a large component of the LVOR under our testing conditions (approximately 30% of the changes in gain but not in phase due to training.

Adaptation, Physiological↗
PubMed1999

Self-administration of cocaine analogs by rats.

RATIONALE: A novel scheme for the synthesis of cocaine analogs from vinylcarbenoid precursors has made available compounds that have a diverse range of affinities for the DA and 5-HT transporters. These compounds were used to explore the relationship between their biochemical properties and their reinforcing effects. OBJECTIVES: The objective was to assess the reinforcing efficacy of selected cocaine analogs and compare the results with their selectivity in binding to DA and 5-HT transporters. METHODS: Rats were prepared with chronically indwelling intravenous cannulae and trained to self-administer cocaine on a progressive ratio (PR) schedule. A range of doses of seven cocaine analogs were substituted for cocaine in separate groups of animals. RESULTS: The results demonstrate a wide range of reinforcing efficacies and potencies among the seven selected drugs. Four tropane analogs (WF-11, WF-23, WF-24, WF-55) were found to support self-administration behavior on a PR schedule while three did not (WF-31, WF-54 and WF-60). The DA/5-HT selectivity ratio was found to be a better predictor of self-administration behavior than affinity at the DA transporter alone. CONCLUSION: These data suggest that drugs with a higher affinity for the DA versus the 5-HT transporter are more likely to be self-administered.

Animals↗
PubMed1999

The GABA(B) agonist CGP 44532 decreases cocaine self-administration in rats: demonstration using a progressive ratio and a discrete trials procedure.

Previous self-administration experiments have shown that baclofen, the prototypical GABA(B) agonist, produces an apparent attenuation in the reinforcing effects of cocaine in rats. The present experiments examined the effects of CPG 44532, a novel and highly specific GABA(B) agonist, on cocaine self-administration using two distinctly different procedures. CGP 44532 (0.063-0.5 mg/kg) produced a dose dependent decrease in break point on a progressive-ratio (PR) schedule. A low dose of CGP 44532 (0.125 mg/kg) produced an apparent shift of the cocaine dose-response curve to the right. In contrast there was comparatively little effect on food-reinforced responding on the same PR schedule. Using a discrete-trials procedure that engendered a circadian pattern of self-administration, CPG 44532 (0.063-0.5 mg/kg) produced a dose-dependent suppression of cocaine intake in the 4 h period following treatment. When a concurrently available food reinforced lever was added to the discrete trials paradigm CGP 44532 failed to disrupt responding for food at any of the doses tested. Data from the PR and discrete-trials procedures taken together indicate that CGP 44532 produced a specific decrease in the motivation to self-administer cocaine.

Animals↗
PubMed1999

Long-term changes in connexin32 gap junction protein and mRNA expression following cocaine self-administration in rats.

Considerable evidence indicates a critical role for dopamine in the reinforcing effects of cocaine. Because dopamine has been shown to be a critical modulator of gap junction communication in both eye and brain, we sought to examine whether extended intravenous cocaine self-administration would affect the expression of gap junction channel-forming proteins (connexins). Using ELISA, Western analysis, immunohistochemistry, semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR), and non-radioactive in situ hybridization, we demonstrate that withdrawal from chronic cocaine self-administration causes lasting changes in connexin32 (Cx32) expression in the nucleus accumbens and hippocampus at 2, 7 and 21 days after the last cocaine injection. A sustained decrease in Cx32 protein and mRNA levels is noted in areas that have been implicated in cocaine craving (i.e. nucleus accumbens and subfields of the hippocampal formation). A progressive increase in gap junction protein and mRNA expression is noted in areas that become hyperexcitable after chronic cocaine exposure (i.e. CA1 hippocampal neurons). We speculate that gap junction communication may be critically involved in reinforcement processes and neuroadaptive changes produced by drugs of abuse.

Animals↗
PubMed1999

Fish oil feeding delays influenza virus clearance and impairs production of interferon-gamma and virus-specific immunoglobulin A in the lungs of mice.

Ingestion of fish oil can suppress the inflammatory response to injury and may impair host resistance to infection. To investigate the effect of a diet containing fish oil on immunity to viral infection, 148 BALB/c mice were fed diets containing 3 g/100 g of sunflower oil with either 17 g/100 g of fish oil or beef tallow for 14 d before intranasal challenge with live influenza virus. At d 1 and d 5 after infection, the mice fed fish oil had higher lung viral load and lower body weight (P < 0.05). In addition to the greater viral load and weight loss at d 5 after infection, the fish oil group consumed less food (P < 0.05) while the beef tallow group was clearing the virus, had regained their preinfection weights and was returning to their preinfection food consumption. The fish oil group had impaired production of lung interferon-gamma (IFN-gamma), serum immunoglobulin (Ig) G and lung IgA-specific antibodies (all P < 0. 05) although lung IFN-alpha/beta and the relative proportions of bronchial lymph node CD4+ and CD8+ T lymphocytes did not differ between groups after infection. The present study demonstrates a delay in virus clearance in mice fed fish oil associated with reduced IFN-gamma and antibody production and a greater weight loss and suppression of appetite following influenza virus infection. However, differences observed during the course of infection did not affect the ultimate outcome as both groups cleared the virus and returned to preinfection food consumption and body weight by d 7.

Animals↗
PubMed1998

Platelet activating factor receptor expression is associated with neuronal apoptosis in an in vivo model of excitotoxicity.

Platelet activating factor (PAF), an endogenous proinflammatory agent, mediates neuronal survival, glutamate release, and transcriptional activation following excitotoxin challenge. To determine whether PAF receptor (PAFR) expression is altered during excitotoxicity, changes in PAFR mRNA localization were compared with markers of neuronal apoptosis and reactive gliosis following systemic injection of kainic acid. Data from semi-quantitative RT-PCR, in situ hybridization, DNA fragmentation, cellular morphology analysis, and immunohistochemistry demonstrate that the localization of PAFR mRNA is altered during kainic acid-induced neurodegeneration. While PAFR mRNA is normally exhibited by neurons and microglia in rat hippocampus, expression becomes restricted to apoptotic neurons and to glia involved in phagocytosing apoptotic debris following treatment with excitotoxin. PAFR mRNA is rarely detected in surviving neurons. These data provide the first indication that PAFR-expressing neurons may be preferentially susceptible to excitotoxic challenge.

Animals↗
PubMed1998

Effect of horizontal vergence on the motor and sensory components of vertical fusion.

PURPOSE: To compare motor and sensory capabilities for fusion of vertical disparities at different angles of horizontal vergence in healthy humans. METHODS: Eye movements were recorded from both eyes of 12 healthy subjects using three-axis search coils. The stimulus was a cross (+) (3.4 x 3.2 degrees , vertically and horizontally, respectively) presented to each eye with a stereoscopic display. Vertical disparities were introduced by adjusting the vertical position of the cross in front of one eye. The disparity was increased in small increments (0.08 degrees ) every 8 seconds. Viewing was defined as "near" if there was a horizontal disparity that elicited 6 degrees to 15 degrees convergence, depending on the subject's capability for horizontal fusion; viewing was defined as "far" at 1 degrees convergence. Maximum motor (measured), sensory (stimulus minus motor), and total (motor plus sensory) vertical fusion were compared. RESULTS: In 9 (75%) of 12 subjects the maximum total vertical fusion was more in near than in far viewing. The three who did not show this effect had relatively weak horizontal fusion. For the entire group, the motor component differed significantly between far (mean, 1.42 degrees ) and near (mean, 2.13 degrees). Total vertical fusion capability (motor plus sensory) also differed significantly between far (mean, 1.68 degrees ) and near (mean, 2.39 degrees ). For the sensory component there was no difference between between far (mean, 0.268 degrees ) and near (mean, 0.270 degrees ). As vertical disparity increased in a single trial, however, there was a small gradual increase of the contribution of the sensory component to vertical fusion. CONCLUSIONS: Vertical fusion capability usually increases with convergence. This increase is caused primarily by an increase in the motor component. There is a gradual but small increase in the sensory component as target disparity slowly increases.

Adult↗
PubMed1997

Baclofen suppression of cocaine self-administration: demonstration using a discrete trials procedure.

We have previously reported that rats display a circadian pattern of cocaine self-administration if access to drug is limited to 10-min discrete trials that are separated by at least 20 min. In the present study, the pattern of cocaine intake (1.5 mg/kg per injection) was studied in two large groups of animals that were maintained on different 12-h light/dark cycles (3 a.m. to 3 p.m. versus 10 a.m. to 10 p.m.). Regardless of the time of light onset, a circadian pattern of cocaine self-administration was observed. Maximum cocaine intake occurred during the final 6 h of the dark period and was followed by a relative abstinence period during the light phase. This highly predictable pattern of drug taking behavior provided an opportunity to explore the effect of baclofen, a GABAB agonist, on the initiation of self-administration behavior. In two separate studies, acute treatment with baclofen (1.25-5.0 mg/kg) was shown to suppress cocaine intake for at least 4 h. Baclofen had no significant effect on responding for food reinforcement. Previous results have indicated that baclofen appears to reduce specifically the motivation to respond for cocaine. Together, these data suggest that baclofen should be considered as a possible pharmacotherapeutic agent in cocaine addiction.

Animals↗
PubMed1997

A critique of fixed and progressive ratio schedules used to examine the neural substrates of drug reinforcement.

This paper is a critique of fixed and progressive ratio schedules used to examine the neural substrates of cocaine reinforcement. The discussion focuses on problems encountered while examining the effects of neurotoxic lesions and pharmacological pretreatments on cocaine reinforcement. We review the theoretical and interpretational problems associated with the use of the fixed ratio (FR) schedules that have been used in the majority of studies, and we conclude that rate of drug intake cannot directly address the issue of increased or decreased reinforcer efficacy. The progressive ratio (PR) schedule offers some advantages over FR schedules, although it is now clear that the same implementation cannot be applied across all drug classes. It is likely that the motivation to self-administer psychostimulant vs. opiate drugs is qualitatively different. We conclude that there is no single schedule that can quantify all aspects of drug reinforcement and that behavioral paradigms will need to be adapted according to the particular question under study.

Animals↗
PubMed1997

Psyllium-enriched cereals lower blood total cholesterol and LDL cholesterol, but not HDL cholesterol, in hypercholesterolemic adults: results of a meta-analysis.

We conducted a meta-analysis to determine the effect of consumption of psyllium-enriched cereal products on blood total cholesterol (TC), LDL cholesterol (LDL-C) and HDL cholesterol (HDL-C) levels and to estimate the magnitude of the effect among 404 adults with mild to moderate hypercholesterolemia (TC of 5.17-7.8 mmol/L) who consumed a low fat diet. Studies of psyllium cereals were identified by a computerized search of MEDLINE and Current Contents and by contacting United States-based food companies involved in psyllium research. Published and unpublished studies were reviewed by one author and considered eligible for inclusion in the meta-analysis if they were conducted in humans, were randomized, controlled experiments, and included a control group that ate cereal providing </=3 g soluble fiber/d. Eight published and four unpublished studies, conducted in four countries, met the criteria. Analysis of a linear model was performed, controlling for sex and age. Female subjects were divided into two groups to provide a rough estimate of the effect of menopausal status (premenopausal = <50 y, postmenopausal = >/=50 y) on blood lipids. The meta-analysis showed that subjects who consumed a psyllium cereal had lower TC and LDL-C concentrations [differences of 0.31 mmol/L (5%) and 0.35 mmol/L (9%), respectively] than subjects who ate a control cereal; HDL-C concentrations were unaffected in subjects eating psyllium cereal. There was no effect of sex, age or menopausal status on blood lipids. Results indicate that consuming a psyllium-enriched cereal as part of a low fat diet improves the blood lipid profile of hypercholesterolemic adults over that which can be achieved with a low fat diet alone.

Adult↗