Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Natural Science Disciplines”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

620 records · Page 35Linked to original sources
PubMed2003

Differences in the hemodynamic response to event-related motor and visual paradigms as measured by near-infrared spectroscopy.

Several current brain imaging techniques rest on the assumption of a tight coupling between neural activity and hemodynamic response. The nature of this neurovascular coupling, however, is not completely understood. There is some evidence for a decoupling of these processes at the onset of neural activity, which manifests itself as a momentary increase in the relative concentration of deoxyhemoglobin (HbR). The existence of this early component of the hemodynamic response function, however, is controversial, as it is inconsistently found. Near infrared spectroscopy (NIRS) allows quantification of levels of oxyhemoglobin (HbO(2)) and HbR during task performance in humans. We acquired NIRS data during performance of simple motor and visual tasks, using rapid-presentation event-related paradigms. Our results demonstrate that rapid, event-related NIRS can provide robust estimates of the hemodynamic response without artifacts due to low-frequency signal components, unlike data from blocked designs. In both the motor and visual data the onset of the increase in HbO(2) occurs before HbR decreases, and there is a poststimulus undershoot. Our results also show that total blood volume (HbT) drops before HbO(2) and undershoots baseline, raising a new issue for neurovascular models. We did not find early deoxygenation in the motor data using physiologically plausible values for the differential pathlength factor, but did find one in the visual data. We suggest that this difference, which is consistent with functional magnetic resonance imaging (fMRI) data, may be attributable to different capillary transit times in these cortices.

Adult↗
PubMed1998

Biology as technology.

In this paper we have emphasised the technological dimension of the biosciences, especially the biosciences of our time. As a straight forward fact this dimension is less controversial than the question of its relevance is. We have argued that the existence of this dimension is a consequence of the empirical character of the biosciences (as well as of the sciences in general). Knowledge of nature can be achieved only if the subject of knowledge is able to gain access to natural phenomena, and technological means have become increasingly necessary for achieving this. The more that is already known, the greater the technological investment required to produce new knowledge. Therefore there is an interrelationship between the advancement of knowledge and the amount and complexity of the research technology required. It would be short sighted to conclude from this observation that human imagination and inventiveness have become superfluous. Nevertheless the growing preponderance of technological means for progress in science is undeniable. A particularly important insight is that this process not only involves a quantitative increase in technology within science. Our main hypothesis is that there is a close relationship between the type of means used, the type of subject required for performing research, the kinds of objects investigated in science, and the nature of the results that are generated. We have tried to illustrate this by distinguishing between three different types of bioscience: (a) a descriptive type, (b) an experimental type, and (c) and an industrial type. Without pretending this provides a universal key to the history of the biosciences and to understanding of the way science works today, we hope that such a distinction may open up new avenues of thought. We hope that this approach will provide us with a more realistic picture of science. The propositional view reduces science to its theoretical results, in particular to the theories emanating from basic research. Science is seen as a special kind of philosophy; its central aim is to provide us with a 'true' view of the world. Thus the social problems which result from scientific inquiry and from the application of its results seem to be something external to the very essence of science and thus only of secondary importance. We believe, therefore, that this picture of science is both theoretically unsatisfactory and socially misleading. An appropriate account of science cannot ignore the fact that basic research represents only a very small part of the science system of our time. It cannot neglect the fact that science today is steeped with technology and to a great extent also industrialised. And it cannot treat the social problems of science as something merely 'external'. To view science as an activity in the sense outlined in this paper permits one to integrate these different aspects into one coherent and realistic picture. 1. It is obvious that technology plays a crucial role in determining the social reality of science. This is mainly because of the high costs of contemporary research technology that science can no longer be performed by gentleman scientists like Alexander von Humboldt or Charles Darwin, who not only financed their own living but the cost of their own research too. Science today is a profession, and in many cases it can be performed only in large groups or institutions financed by the state or by private companies. At the same time this means that it is more and more dependent upon decisions made outside science. Scientific activities have assumed the economic form of wage labour. The internal structure of science is characterised by a division of labour and hierarchical forms of decision making. 2. From a more traditional point this may seem to be a development 'external' to science, without any relevance for its 'essence'. The aim of science, it may be said, is to discover the truth about the external world, and the ways of reaching it a

Biological Science Disciplines↗
PubMed1996

Effect of SLS-2 spaceflight on immunologic parameters of rats.

During the Spacelab Life Sciences-2 mission, rats were dissected in space and biosamples were returned to Earth for analysis. Immunologic studies addressed the kinetics of T lymphocyte proliferative responses, cytotoxic activity of natural killer cells, and cytokine production. Experiments were performed by using spleen and bone marrow of rats dissected before flight, during flight, immediately after landing of the space shuttle (R + 0), or 14 days after landing (R + 14), as well as those of respective control animals. Each group consisted of five male Sprague-Dawley rats. It was demonstrated that T lymphocyte activity of rats dissected in flight was significantly decreased compared with the controls. This was observed during 48-, 72-, and 96-h cultivation and stimulation with the following mitogenic stimuli: concanavalin A (Con A; 0.1, 1.0, and 10.0 mg/ml), phytohemagglutinin (PHA; 2.5 mg/ml), and interleukin-2 (IL-2; 1 U/ml). The cell proliferation rate in rats dissected immediately after landing did not decrease, whereas that in rats dissected at R + 14 increased. The activity of spleen natural killer cells was reduced in response to 51Cr-labeled target cells during flight (YAC-1 and K-562) and after flight (YAC-1). At R + 14, their activity returned to normal. Another technique employed to measure natural cytotoxicity, using [3H]uridine-labeled target cells and ribonuclease, did not reveal any differences between control and experimental groups. In bone marrow, the activity of natural killer cells did not vary significantly. The production of IL-1, IL-2, tumor necrosis factor (TNF)-alpha, and TNF-beta in spleen cell cultures of the flight rats was reduced. At R + 0, IL-1 and TNF-beta levels remained lowered, whereas TNF-alpha was increased. At R + 0, interferon-alpha and interferon-gamma levels were diminished. In summary, cell-mediated immunity in rats was significantly suppressed during flight. The time course variation of immune parameters after flight suggests that the changes may truly indicate a response of the immune system to spaceflight conditions that could increase over time.

Animals↗
PubMed2003

An in silico assessment of gene function and organization of the phenylpropanoid pathway metabolic networks in Arabidopsis thaliana and limitations thereof.

The Arabidopsis genome sequencing in 2000 gave to science the first blueprint of a vascular plant. Its successful completion also prompted the US National Science Foundation to launch the Arabidopsis 2010 initiative, the goal of which is to identify the function of each gene by 2010. In this study, an exhaustive analysis of The Institute for Genomic Research (TIGR) and The Arabidopsis Information Resource (TAIR) databases, together with all currently compiled EST sequence data, was carried out in order to determine to what extent the various metabolic networks from phenylalanine ammonia lyase (PAL) to the monolignols were organized and/or could be predicted. In these databases, there are some 65 genes which have been annotated as encoding putative enzymatic steps in monolignol biosynthesis, although many of them have only very low homology to monolignol pathway genes of known function in other plant systems. Our detailed analysis revealed that presently only 13 genes (two PALs, a cinnamate-4-hydroxylase, a p-coumarate-3-hydroxylase, a ferulate-5-hydroxylase, three 4-coumarate-CoA ligases, a cinnamic acid O-methyl transferase, two cinnamoyl-CoA reductases) and two cinnamyl alcohol dehydrogenases can be classified as having a bona fide (definitive) function; the remaining 52 genes currently have undetermined physiological roles. The EST database entries for this particular set of genes also provided little new insight into how the monolignol pathway was organized in the different tissues and organs, this being perhaps a consequence of both limitations in how tissue samples were collected and in the incomplete nature of the EST collections. This analysis thus underscores the fact that even with genomic sequencing, presumed to provide the entire suite of putative genes in the monolignol-forming pathway, a very large effort needs to be conducted to establish actual catalytic roles (including enzyme versatility), as well as the physiological function(s) for each member of the (multi)gene families present and the metabolic networks that are operative. Additionally, one key to identifying physiological functions for many of these (and other) unknown genes, and their corresponding metabolic networks, awaits the development of technologies to comprehensively study molecular processes at the single cell level in particular tissues and organs, in order to establish the actual metabolic context.

Arabidopsis↗
PubMed2004

Phosphate binding protein as the biorecognition element in a biosensor for phosphate.

This work explores the potential use of a member of the periplasmic family of binding proteins, the phosphate binding protein (PBP), as the biorecognition element in a sensing scheme for the detection of inorganic phosphate (Pi). The selectivity of this protein originates from its natural role which, in Escherichia coli, is to serve as the initial receptor for the highly specific translocation of Pi to the cytoplasm. The single polypeptide chain of PBP is folded into two similar domains connected by three short peptide linkages that serve as a hinge. The Pi binding site is located deep within the cleft between the two domains. In the presence of the ligand, the two globular domains engulf the former in a hinge-like manner. The resultant conformational change constitutes the basis of the sensor development. A mutant of PBP (MPBP), where an alanine was replaced by a cysteine residue, was prepared by site-directed mutagenesis using the polymerase chain reaction (PCR). The mutant was expressed, from plasmid pSD501, in the periplasmic space of E. coli and purified in a single chromatographic step on a perfusion anion-exchange column. Site-specific labeling was achieved by attaching the fluorophore, N-[2-(1-maleimidyl)ethyl]-7-(diethylamino)coumarin-3-carboxamide (MDCC), to the protein through the sulfhydryl group of the cysteine moiety. Steady-state fluorescence studies of the MPBP-MDCC conjugate showed a change in the intensity of the signal upon addition of Pi. Calibration curves for Pi were constructed by relating the intensity of the fluorescence signal with the amount of analyte present in the sample. The sensing system was first developed and optimized on a spectrofluorometer using ml volumes of sample. It was then adapted to be used on a microtiter plate arrangement with microliter sample volumes. The system's versatility was finally proven by developing a fiber optic fluorescence-based sensor for monitoring Pi. In all three cases the detection limits for the analyte were in the sub-microMolar range. It was also demonstrated that the sensing system was selective for phosphate over other structurally-similar anions, paving the way for the design and development of a new family of biosensors utilizing the specific binding properties of periplasmic proteins.

Amino Acid Substitution↗
PubMed2006

Data withholding and the next generation of scientists: results of a national survey.

PURPOSE: To provide the first national data on the nature, extent, and consequences of withholding among life science trainees. METHOD: In 2003, the authors surveyed 1,077 second-year doctoral students and postdoctoral fellows in life sciences at 50 U.S. universities, with a comparison group of trainees in computer science and chemical engineering. The study variables examined trainees' exposure to and the consequences of data withholding. RESULTS: Two hundred forty-six trainees (23.0%) reported that they had asked for and been denied access to information, data, materials, or programming associated with published research and 221 (20.6%) to unpublished research. Eighty-five trainees (7.9%) reported that they had denied another academic scientist's request(s) related to their own published research. Five hundred thirty-three trainees (50.8%) reported that withholding had had a negative effect on the progress of their research, 508 (48.5%) on the rate of discovery in their lab/research group, 472 (45.0%) on the quality of their relationships with academic scientists, 346 (33.0%) on the quality of their education, and 299 (28.5%) on the level of communication in their lab/research group. Trainees denied access to research were significantly more likely to report that data withholding had had a negative effect on several aspects of the educational experience. CONCLUSIONS: Data withholding had demonstrated negative effects on trainees. The life sciences, more so than chemical engineering or computer science, will have to address this issue among its trainees. Failure to do so could result in delayed research, inefficient training, and a culture of withholding among future life scientists.

Access to Information↗
PubMed1994

Single track effects, Biostack and risk assessment.

The scientific career of Prof. Bucker has spanned a very exciting period in the fledgling science of Space Radiation Biology. The capability for placing biological objects in space was developed, and the methods for properly packaging, retrieving and analyzing them were worked out. Meaningful results on the effects of radiation were obtained for the first time. In fact, many of the successful techniques and methodologies for handling biological samples were developed in Prof. Bucker's laboratories, as attested by the extensive Biostack program. He was the first to suggest and successfully carry out experiments in space directly aimed at measuring effects of single tracks of high-energy heavy galactic cosmic rays by specifically identifying whether or not the object had been hit by a heavy particle track. Because the "hit" frequencies of heavy galactic cosmic rays to cell nuclei in the bodies of space travelers will be low, it is expected that any effects to humans on the cellular level will be dominated by single-track cell traversals. This includes the most important generally recognized late effect of space radiation exposure: radiation-induced cancer. This paper addresses the single-track nature of the space radiation environment, and points out the importance of single "hits" in the evaluation of radiation risk for long-term missions occurring outside the earth's magnetic field. A short review is made of biological objects found to show increased effects when "hit" by a single heavy charged-particle in space. A brief discussion is given of the most provocative results from the bacterial spore Bacillus subtilis: experimental evidence that tracks can affect biological systems at much larger distances from the trajectory than previously suspected, and that the resultant inactivation cross section in space calculated for this system is very large. When taken at face value, the implication of these results, when compared to those from experiments performed at ground-based accelerators with beams at low energies in the same LET range, is that high-energy particles can exert their influence a surprising distance from their trajectory and the inactivation cross sections are some 20 times larger than expected. Clearly, beams from high-energy heavy-ion accelerators should be used to confirm these results. For those end points that can also be caused by low-LET beams such as high-energy protons, it is important to measure their action cross sections as well. The ratio of the cross sections for a high-LET beam to that of a low-LET beam is an interesting experimental ratio and, we suggest, of more intrinsic interest than the RBE (Relative Biological Effectiveness). It is a measure of the "biological" importance of one particle type relative to another particle type. This ratio will be introduced and given the name RPPE (Relative Per Particle Effectiveness). Values of RPPE have appeared in the literature and will be discussed. A rather well-known value of this quantity (13,520) has been suggested for the RPPE of high-energy iron ions to high-energy protons. This value was suggested by Letaw et al. Nature 330, 709-710 (1987)] we will call it the Letaw limit. It will be discussed in terms of the importance of the heavy-ion component vs light-ion component of the galactic cosmic rays. It is also pointed out, however, that there may be unique effects from single tracks of heavy ions that do not occur from light-ion tracks. For such effects, the concepts of both RBE and RPPE lose their meaning.

Bacillus subtilis↗
PubMed2002

Complexities in ETS-domain transcription factor function and regulation: lessons from the TCF (ternary complex factor) subfamily. The Colworth Medal Lecture.

The ETS-domain transcription factor family can be divided into a series of subfamilies. Elk-1 represents the founding member of the ternary complex factor (TCF) subfamily. By focusing on the TCF subfamily, we can demonstrate the complexities that exist in the function and regulation of ETS-domain transcription factors. This article focuses on Elk-1 in detail and summarizes the functions of other TCFs. The key themes covered include the domain structure of the TCFs, the mechanisms of complex formation with serum response factor, regulation of TCFs by mitogen-activated protein kinase cascades, and transcriptional regulatory properties of the TCFs. Finally, the emerging role of the TCFs in vivo is discussed. A picture is developing indicating that, while these proteins exhibit significant sequence and functional conservation, key differences in their structure and regulation are being identified which may relate to unique functions of these proteins in vivo.

Amino Acid Sequence↗