PubMed Health⌕ Search

Biomedical subjects

B Roberts

Publications and source records attributed to B Roberts.

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

Effects of differences in timbre on sequential grouping.

Differences in the timbre of sounds in a sequence can affect their perceptual organization. Using a performance measure, Hartmann and Johnson (1991) concluded that streaming could be predicted primarily by the extent to which sounds were passed by different peripheral channels. However, results from a rating task by Dannenbring and Bregman (1976) suggested that sounds in the same spectral region (passed by the same peripheral channels) can be allocated to different streams. In Experiment 1, it was found, using an interleaved melody task, that target sounds could be selected from distractors in the same spectral region more easily when they differed in timbre. This finding might result from primitive stream segregation or schema-driven selection, but not from peripheral channeling. In Experiment 2, a rhythm discrimination task was used, requiring the sounds to be integrated for good performance. Differences in timbre impaired performance, indicating the occurrence of primitive stream segregation.

Attention↗
PubMed1999

Enhanced immune response to the melanoma antigen gp100 using recombinant adenovirus-transduced dendritic cells.

Glycoprotein 100 (gp100) is one of a series of well-characterized human melanoma-associated antigens expressed by most melanoma cells. Immunization of C57BL/6 mice with an adenovirus (Ad) vector encoding human gp100 (Adhgp100) has been shown to induce limited protective immunity against challenge with murine melanoma B16 cells. In the current study we determined whether gp100-specific immunity can be enhanced using bone-marrow-derived dendritic cells (DCs) transduced with Adhgp100 ex vivo. Subcutaneous injection of Adhgp100-infected DCs resulted in potent T-cell-mediated protective immunity and a greater than 80% reduction of established tumors when administered to B16 tumor-bearing hosts. Compared to direct injection of Adhgp100 vector alone, immunization with Adhgp100-infected DCs induced markedly greater antitumor activity. In vitro CTL analysis demonstrated that DC-Adhgp100 immunization activated both CD4(+) and CD8(+) CTLs, while no lytic activity was generated by vaccination with Adhgp100 alone. In vivo depletion of CD4(+) T cells, but not CD8(+) T cells, completely abrogated CTL activity, suggesting that Adhgp100-transduced DCs result in activation of both CD4(+) and CD8(+) CTLs via a CD4(+)-dependent mechanism. We speculate that this improved efficacy of Adhgp100-transduced DCs compared to direct immunization with Adhgp100 may be the result of direct DC-mediated CD4(+) T cell activation. These results emphasize the importance of CD4(+) T cells in the development of therapeutic antigen-specific cancer vaccines.

Adenoviridae↗
PubMed1999

Psychiatric research ethics: an overview of evolving guidelines and current ethical dilemmas in the study of mental illness.

The field of psychiatry has an opportunity to construct a more refined, perhaps more enduring understanding of the ethical basis of mental illness research. The aim of this paper is to help advance this understanding by 1) tracing the evolution of the emerging ethic for biomedical experimentation, including recent recommendations of the President's National Bioethics Advisory Commission, and 2) reviewing data and concepts related to compelling ethical questions now faced in the study of mental disorders. Empirical findings on informed consent, the ethical safeguards of institutional review and surrogate decision making, and the relationship between scientific and ethical imperatives are outlined. Psychiatric researchers will increasingly be called upon to justify their scientific approaches and to seek ways of safeguarding the well-being of people with mental illness who participate in experiments. Most importantly, psychiatric investigators will need to demonstrate their appreciation and respect for ethical dimensions of investigation with special populations. Further empirical study and greater sophistication with respect to the distinct ethical issues in psychiatric research are needed. Although such measures present many challenges, they should not interfere with progress in neuropsychiatric science so long as researchers in our field seek to guide the process of reflection and implementation.

Bioethics↗
PubMed1999

TRACE observation of damped coronal loop oscillations: implications for coronal heating

The imaging telescope on board the Transition Region and Coronal Explorer (TRACE) spacecraft observed the decaying transversal oscillations of a long [(130 +/- 6) x 10(6) meters], thin [diameter (2.0 +/- 0.36) x 10(6) meters], bright coronal loop in the 171 angstrom Fe(IX) emission line. The oscillations were excited by a solar flare in the adjacent active region. The decay time of the oscillations is 14.5 +/- 2.7 minutes for an oscillation with a frequency 3.90 +/- 0.13 millihertz. The coronal dissipation coefficient is estimated to be eight to nine orders of magnitude larger than the theoretically predicted classical value. The larger dissipation coefficient may solve existing difficulties with wave heating and reconnection theories.

Journal Article↗
PubMed1999

Effects of similarity in bandwidth on the auditory sequential streaming of two-tone complexes.

We investigated the perceptual grouping of sequentially presented sounds--auditory stream segregation. It is well established that sounds heard as more similar in quality, or timbre, are more likely to be grouped into the same auditory stream. However, it is often unclear exactly what acoustic factors determine timbre. In this study, we presented various sequences of simple sounds, each comprising two frequency components (two-tone complexes), and measured their perceptual grouping. We varied only one parameter between trials, the intercomponent separation for some of the complexes, and examined the effects on stream segregation. Four hypotheses are presented that might predict the extent of streaming. Specifically, least streaming might be expected when the sounds were most similar in either (1) the frequency regions in which they have energy (maximum spectral overlap), (2) their auditory bandwidths, (3) their relative bandwidths, or (4) the rate at which the two components beat together (intermodulation rate). It was found that least streaming occurred when sounds were most similar in either their auditory or their relative bandwidths. Although these two hypotheses could not be distinguished, the results were clearly different from those predicted by hypotheses (1) and (4). The implications for models of stream segregation are discussed.

Auditory Perception↗
PubMed1999

Chronic systemic administration of tumor necrosis factor alpha and HIV gp120: effects on adult rodent brain and blood-brain barrier.

Since tumor necrosis factor alpha (TNF-alpha) and HIV gpl20 glycoprotein are both neurotoxic, the possibility that systemic sources of these two agents mediate AIDS-associated blood-brain barrier (BBB) breakdown and brain damage was tested in two murine models: (1) intramuscular implantation of a TNF-alpha-transfected tumor in nu/nu mice and (2) daily subcutaneous injections of HIV gpl20 in BALB/c mice. The BBB remained intact; brain damage was not found, and apoptotic cell numbers did not increase. These results show that normal adult brain and BBB is unaffected by exposure to TNF-alpha or HIV gpl20 and suggest that severity of brain disease is not directly affected by systemic levels of these compounds.

Animals↗
PubMed1999

HIV infection of choroid plexus in AIDS and asymptomatic HIV-infected patients suggests that the choroid plexus may be a reservoir of productive infection.

The choroid plexus (CPx) may be an important site of viral dissemination since monocytes and dendritic cells in its stroma are infected with HIV in AIDS patients and since the ratio of CPx to brain infection is more than 2 : 1. In order to see if CPx infection also develops in asymptomatic (ASY) HIV-infected patients, we examined archival formalin-fixed brain and CPx from 14 AIDS and seven ASY cases, using routine histology, immunohistochemistry for HIV gp41, and DNA extraction and gene amplification for HIV DNA. Eight of 14 AIDS (57%) had HIV-positive cells in the CPx and four (29%) had HIV encephalitis. Two of seven ASY cases (29%) had HIV-positive cells in the CPx but none had HIV encephalitis. Extracted DNA from brain, CPx and systemic organs of five ASY cases was amplified by nested PCR with or without Southern blotting for HIV env gene. It was positive in systemic organs in five cases; in CPx in four cases; and in brain in one case. This study shows that the CPx is a site of HIV infection in ASY patients and that the frequency of CPx infection is higher than seen in brain in both AIDS and ASY cases. The results are consistent with the hypothesis that the CPx may be a site for hematogeneous spread and a reservoir for HIV infection during the period of clinical latency.

Acquired Immunodeficiency Syndrome↗
PubMed1999

Observations on centrifugation: application to centrifuge development.

This report outlines the background to the development of an automated, serial, discrete centrifuge, reporting on the criteria considered essential in such an instrument. We established the criteria by examining the detailed logistics of centrifuge operation in a hospital laboratory. The mean sample load per run, using six centrifuges, was 13.6 samples, and the user-selectable cycle time ranged from 00:01:10 to 00:12:33 (hours:minutes:seconds) with a fixed g value of 1050. During the laboratory working window, (0900-1700), only 50% of the centrifuge capacity was utilized and more than one-third of the sample workload was delayed for >5 min because the centrifuges were not emptied promptly. In addition, 35% of the sample workload was centrifuged for less than the time prescribed in the operational specifications. Based on these findings, we designed a new continuous, serial centrifuge to overcome some of the deficiencies noted in the logistics study. The centrifuge operates continuously, nominally treating 150 samples/h, with a cycle time of 5 min at 1,000 g. The cycle time and g value are variable between limits, and their selection governs the throughput rate. Each sample is centrifuged separately in individual rotors mounted in a sturdy carousel with a periphery that traverses a load/unload station. There is no sample delay because of operator absence, and the capacity is fully utilized. The centrifuge can operate in a stand-alone capacity or has the capability of being integrated into a sample preparation system or as a direct front end for high-throughput analyzers.

Centrifugation↗
PubMed1999

Bioceramics surface modification by means of osteoclasts in culture.

The specific objectives of this study was: (I) to investigate the effect of various biomedical ceramics such as tricalcium phosphate (TCP), hydroxyapatite (HA), and aluminum-calcium-phosphorous oxide (ALCAP) on the adherence and viability of mice osteoclasts (OT) in vitro, and (II) to evaluate the role of OT that might have on the surfaces of such bioceramics. The OT cells were isolated from adult male mice and seeded at a density of 5 x 10(5) cells/well according to standard laboratory procedures. Cells were plated in each micrometer-well pretreated with ceramic capsules (HA, TCP and ALCAP) and buffered control. At the end of 1, 2, 3 and 5 days, the viability and cell number of OT were determined using an established assay. Cell number was determined in control wells with known number of cells, and a standard curve was generated by plotting absorbency units versus cell number. Biochemical analysis was performed on the aliquots obtained from the experimental and control wells at the end of each phase of the investigation. The data from this experiment suggest that: (I) OT are capable of adhering to the surface of HA, TCP and ALCAP in an in vitro environment for over a 5-day period. (II) Long-term incubation of ceramic capsules with OT revealed that the cells experienced gradual disassociation phenomenon with a greater numbers of cell detachments seen in the ALCAP contained wells. (III) SEM analysis of representative capsules demonstrated that there was an increase in the number of micro/macropores on the surface of the materials after contacting a cellular environment. This observation suggest that the material surface has been modified (TCP > HA = ALCAP). Information obtained from this study provided new insights on the interrelationship between bioceramics and the possible OT response during chronic inflammation at the site of implantation.

Aluminum Compounds↗
PubMed1999

Exposure of transformed and non-transformed phagocytic cells to novel glass ionomers in culture.

The use of glass ionomers as a novel bone cement is currently being investigated. Although acceptable for use as a dental restorative material, there is little information regarding how ionomers interact with inflammatory macrophage cell types. The specific objective of this experiment was to investigate the possible interrelationship between RAW and human monocyte/macrophage cells at the biochemical and morphological level after being in contact with three different dental cement ionomers (Fuji Duet, Fuji IX, and GC-Fuji-Ortho, GC America Inc., Chicago IL) for 72 hours. Transformed RAW macrophages were obtained from the American Type Culture collection (ATCC), and the non-transformed human macrophages were obtained from the peripheral blood of 25 male and female volunteers. The cells were plated at a density of 4 x 10(6) cells/ml in twenty-four well plates. Each plate was divided into four groups of six cells/group. Twenty-four hours after plating, the cells in groups I-III were incubated with Fuji Duet, Fuji IX, GC Fuji Ortho, respectively, and cells in Group IV were incubated with media alone to serve as controls. Immediately after addition of the ionomers, the cellular morphology was monitored for both transformed and non-transformed cells. Cell number data revealed that normal non-transformed cells were similar in number to control cells in media alone. This result suggests that the polymer treatment did significantly alter cellular viability. On the other hand, RAW cell number was markedly reduced in cells treated with ionomers in comparison to cell growing in media alone. The data suggests that the prescence of the ionomer may reduce the proliferation rate of RAW cells. Biochemical analysis of cellular supernatants to determine cellular alterations at 72 hours revealed increased levels of lactate dehydrogenase activity and levels of malionaldehyde bis diethyl acetal in all ionomer-treated groups of RAW cells compared with media alone. Non-transformed macrophages treated with the same ionomers did not differ significantly from the control cells in media alone. However, when comparing the levels of lactate dehydrogenase activity between the transformed and non-transformed cells it was apparent that the normal cells exhibited statistically higher activity than the RAW transformed cells. The results of this study suggest that although the three ionomers tested were found to be highly biocompatible with fully differentiated non-transformed macrophages, the behavior of transformed and non-transformed phagocytic cells towards these ionomers may not be similar under similar conditions.

Biocompatible Materials↗
PubMed1998

Immunizing patients with metastatic melanoma using recombinant adenoviruses encoding MART-1 or gp100 melanoma antigens.

BACKGROUND: The characterization of the genes encoding melanoma-associated antigens MART-1 or gp100, recognized by T cells, has opened new possibilities for the development of immunization strategies for patients with metastatic melanoma. With the use of recombinant adenoviruses expressing either MART-1 or gp100 to immunize patients with metastatic melanoma, we evaluated the safety, immunologic, and potential therapeutic aspects of these immunizations. METHODS: In phase I studies, 54 patients received escalating doses (between 10(7) and 10(11) plaque-forming units) of recombinant adenovirus encoding either MART-1 or gp100 melanoma antigen administered either alone or followed by the administration of interleukin 2 (IL-2). The immunologic impact of these immunizations on the development of cellular and antibody reactivity was assayed. RESULTS: Recombinant adenoviruses expressing MART-1 or gp100 were safely administered. One of 16 patients with metastatic melanoma receiving the recombinant adenovirus MART-1 alone experienced a complete response. Other patients achieved objective responses, but they had received IL-2 along with an adenovirus, and their responses could be attributed to the cytokine. Immunologic assays showed no consistent immunization to the MART-1 or gp100 transgenes expressed by the recombinant adenoviruses. High levels of neutralizing antibody were found in the pretreatment sera of the patients. CONCLUSIONS: High doses of recombinant adenoviruses could be safely administered to cancer patients. High levels of neutralizing antibody present in patients' sera prior to treatment may have impaired the ability of these viruses to immunize patients against melanoma antigens.

Adenoviridae↗
PubMed1998

Use of a cast flexible plate as a hinge substitute in a hinge-lock design removable partial denture framework.

PURPOSE: The use of a hinge for a removable partial denture with an opening labial bow was replaced by the design and construction of a flexible plate incorporated as part of a cobalt-chromium casting. METHODS: Three similar prostheses were constructed and tested in vitro on an endurance test machine. Each test piece completed 12,000 opening and closing operations without fracture, which a previous study showed is a probable life cycle of a typical removable partial denture with a hinged section. RESULTS: This plate provided sufficient flexibility to allow functional operation of the removable partial denture by a patient.

Chromium Alloys↗
PubMed1998

Long-term Doppler echocardiographic results of aortic or mitral valve replacement with Biocor porcine bioprosthesis.

OBJECTIVES: Our objectives were to evaluate the long-term bioprosthetic and cardiac functional outcome after insertion (over a 10-year period) of a new-generation porcine zero pressure-fixed Biocor bioprosthesis, as well as to determine the echocardiographic accuracy for selection of patients requiring reoperation. The long-term systematic Doppler echocardiographic assessment after valve replacement with this bioprosthesis is lacking. METHODS: Between January 1983 and January 1993, we inserted 756 Biocor prostheses in the aortic (619) or mitral (137) positions. All 51 patients who had a reoperation during the follow-up time were evaluated echocardiographically before reoperation. Additionally, 263 of 446 patients (59%) with aortic bioprostheses and 42 of 74 patients (57%) with mitral bioprostheses who were alive in January 1993 had long-term echocardiographic follow-up. RESULTS: Group A: Normally functioning bioprostheses were found in the aortic position in 242 of 263 patients and in the mitral position in 33 of 42 patients. Group B: Thirty patients had abnormal bioprosthetic function. Eleven patients had regurgitation, 3 had a combined lesion, and signs of calcification appeared in 16 patients with aortic valves, all with a peak gradient of above 60 mm Hg. Group C: Patients who had a reoperation (41 aortic and 10 mitral) within the follow-up period were followed up echocardiographically from the detection of a possible valve dysfunction until reoperation, and the findings accorded well with those at operation in 49 of 51 patients. CONCLUSIONS: These findings suggest that, during a long-term follow-up, most bioprostheses function normally, facilitating improved heart function. Abnormalities in a bioprosthesis usually develop gradually, enabling their detection by Doppler echocardiographic evaluations performed regularly or in case of any symptomatic deterioration.

Adult↗
PubMed1998

DAN is a secreted glycoprotein related to Xenopus cerberus.

We report that DAN, a potential cell cycle regulator and tumour suppressor, is a secreted glycoprotein related to Xenopus cerberus. DAN, cerberus, its mouse relative Cer-1/cer-l/Cerberus-like/Cerr1, and the recently described factor DRM/Gremlin, appear to be members of the cystine knot superfamily, which includes TGFbetas and BMPs. Like cerberus and mCer-1, DAN-induced cement glands as well as markers of anterior neural tissue and endoderm in Xenopus animal cap assays, features of BMP signalling blockade. During mouse embryogenesis, Dan was expressed from E8.5 in cranial mesenchyme and somites, then later in limb and facial mesenchyme. The pattern in somites was highly dynamic, with transcripts initially localized to the caudal half of the nascent epithelial somite, then, after maturation, to sclerotomal cells adjacent to the neural tube. Dan was also expressed in the developing myotome. The expression domains include sites in which BMP inhibition is known to be important for development. Thus, DAN appears to be a secreted factor belonging to the cystine knot superfamily, and one of a growing number of antagonists acting to modulate BMP signalling during development.

Amino Acid Sequence↗
PubMed1998

Biopatch--a new concept in antimicrobial dressings for invasive devices.

A randomised controlled trial (RCT) was conducted to assess the reduction in the rate of catheter-related infections associated with the Biopatch dressing (Johnson & Johnson Medical Inc., Arlington, Texas, USA) used for insertion-site management of central venous catheters (CVCs) placed in the intensive care unit. Patients having a CVC placed were randomly assigned to receive either a Biopatch keyhole dressing to the occlusive Opsite IV 3000 (Smith and Nephew Medical Ltd., Hull, UK) (experimental group) or the Opsite IV 3000 alone (control group). There was a very low colonisation rate of CVC tip and skin exit-site swabs in both the experimental group (6 of 17) and the control group (5 of 16). No statistical difference was found between the two groups with regard to CVC or exit-site colonisation. A calculated sample size of 11,000 would be required to statistically demonstrate a 10 per cent reduction in CVC infection rate using the new Biopatch dressing. A much larger RCT would be required to demonstrate the efficacy of this new device.

Adult↗